Fix gcc 4.5.1 miscompiling drivers/char/i8k.c (again)

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / fs / exec.c

/*
 *  linux/fs/exec.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 * #!-checking implemented by tytso.
 */
/*
 * Demand-loading implemented 01.12.91 - no need to read anything but
 * the header into memory. The inode of the executable is put into
 * "current->executable", and page faults do the actual loading. Clean.
 *
 * Once more I can proudly say that linux stood up to being changed: it
 * was less than 2 hours work to get demand-loading completely implemented.
 *
 * Demand loading changed July 1993 by Eric Youngdale.   Use mmap instead,
 * current->executable is only used by the procfs.  This allows a dispatch
 * table to check for several different types  of binary formats.  We keep
 * trying until we recognize the file or we run out of supported binary
 * formats. 
 */

#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/mm.h>
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <linux/smp_lock.h>
#include <linux/swap.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/perf_event.h>
#include <linux/highmem.h>
#include <linux/spinlock.h>
#include <linux/key.h>
#include <linux/personality.h>
#include <linux/binfmts.h>
#include <linux/utsname.h>
#include <linux/pid_namespace.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/proc_fs.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/tsacct_kern.h>
#include <linux/cn_proc.h>
#include <linux/audit.h>
#include <linux/tracehook.h>
#include <linux/kmod.h>
#include <linux/fsnotify.h>
#include <linux/fs_struct.h>
#include <linux/pipe_fs_i.h>

#include <asm/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/tlb.h>
#include "internal.h"

int core_uses_pid;
char core_pattern[CORENAME_MAX_SIZE] = "core";
unsigned int core_pipe_limit;
int suid_dumpable = 0;

/* The maximal length of core_pattern is also specified in sysctl.c */

static LIST_HEAD(formats);
static DEFINE_RWLOCK(binfmt_lock);

int __register_binfmt(struct linux_binfmt * fmt, int insert)
{
        if (!fmt)
                return -EINVAL;
        write_lock(&binfmt_lock);
        insert ? list_add(&fmt->lh, &formats) :
                 list_add_tail(&fmt->lh, &formats);
        write_unlock(&binfmt_lock);
        return 0;       
}

EXPORT_SYMBOL(__register_binfmt);

void unregister_binfmt(struct linux_binfmt * fmt)
{
        write_lock(&binfmt_lock);
        list_del(&fmt->lh);
        write_unlock(&binfmt_lock);
}

EXPORT_SYMBOL(unregister_binfmt);

static inline void put_binfmt(struct linux_binfmt * fmt)
{
        module_put(fmt->module);
}

/*
 * Note that a shared library must be both readable and executable due to
 * security reasons.
 *
 * Also note that we take the address to load from from the file itself.
 */
SYSCALL_DEFINE1(uselib, const char __user *, library)
{
        struct file *file;
        char *tmp = getname(library);
        int error = PTR_ERR(tmp);

        if (IS_ERR(tmp))
                goto out;

        file = do_filp_open(AT_FDCWD, tmp,
                                O_LARGEFILE | O_RDONLY | FMODE_EXEC, 0,
                                MAY_READ | MAY_EXEC | MAY_OPEN);
        putname(tmp);
        error = PTR_ERR(file);
        if (IS_ERR(file))
                goto out;

        error = -EINVAL;
        if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
                goto exit;

        error = -EACCES;
        if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
                goto exit;

        fsnotify_open(file->f_path.dentry);

        error = -ENOEXEC;
        if(file->f_op) {
                struct linux_binfmt * fmt;

                read_lock(&binfmt_lock);
                list_for_each_entry(fmt, &formats, lh) {
                        if (!fmt->load_shlib)
                                continue;
                        if (!try_module_get(fmt->module))
                                continue;
                        read_unlock(&binfmt_lock);
                        error = fmt->load_shlib(file);
                        read_lock(&binfmt_lock);
                        put_binfmt(fmt);
                        if (error != -ENOEXEC)
                                break;
                }
                read_unlock(&binfmt_lock);
        }
exit:
        fput(file);
out:
        return error;
}

#ifdef CONFIG_MMU

void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
{
        struct mm_struct *mm = current->mm;
        long diff = (long)(pages - bprm->vma_pages);

        if (!mm || !diff)
                return;

        bprm->vma_pages = pages;

        down_write(&mm->mmap_sem);
        mm->total_vm += diff;
        up_write(&mm->mmap_sem);
}

struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
                int write)
{
        struct page *page;
        int ret;

#ifdef CONFIG_STACK_GROWSUP
        if (write) {
                ret = expand_stack_downwards(bprm->vma, pos);
                if (ret < 0)
                        return NULL;
        }
#endif
        ret = get_user_pages(current, bprm->mm, pos,
                        1, write, 1, &page, NULL);
        if (ret <= 0)
                return NULL;

        if (write) {
                unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
                struct rlimit *rlim;

                acct_arg_size(bprm, size / PAGE_SIZE);

                /*
                 * We've historically supported up to 32 pages (ARG_MAX)
                 * of argument strings even with small stacks
                 */
                if (size <= ARG_MAX)
                        return page;

                /*
                 * Limit to 1/4-th the stack size for the argv+env strings.
                 * This ensures that:
                 *  - the remaining binfmt code will not run out of stack space,
                 *  - the program will have a reasonable amount of stack left
                 *    to work from.
                 */
                rlim = current->signal->rlim;
                if (size > rlim[RLIMIT_STACK].rlim_cur / 4) {
                        put_page(page);
                        return NULL;
                }
        }

        return page;
}

static void put_arg_page(struct page *page)
{
        put_page(page);
}

static void free_arg_page(struct linux_binprm *bprm, int i)
{
}

static void free_arg_pages(struct linux_binprm *bprm)
{
}

static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
                struct page *page)
{
        flush_cache_page(bprm->vma, pos, page_to_pfn(page));
}

static int __bprm_mm_init(struct linux_binprm *bprm)
{
        int err;
        struct vm_area_struct *vma = NULL;
        struct mm_struct *mm = bprm->mm;

        bprm->vma = vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
        if (!vma)
                return -ENOMEM;

        down_write(&mm->mmap_sem);
        vma->vm_mm = mm;

        /*
         * Place the stack at the largest stack address the architecture
         * supports. Later, we'll move this to an appropriate place. We don't
         * use STACK_TOP because that can depend on attributes which aren't
         * configured yet.
         */
        vma->vm_end = STACK_TOP_MAX;
        vma->vm_start = vma->vm_end - PAGE_SIZE;
        vma->vm_flags = VM_STACK_FLAGS;
        vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);

        err = security_file_mmap(NULL, 0, 0, 0, vma->vm_start, 1);
        if (err)
                goto err;

        err = insert_vm_struct(mm, vma);
        if (err)
                goto err;

        mm->stack_vm = mm->total_vm = 1;
        up_write(&mm->mmap_sem);
        bprm->p = vma->vm_end - sizeof(void *);
        return 0;
err:
        up_write(&mm->mmap_sem);
        bprm->vma = NULL;
        kmem_cache_free(vm_area_cachep, vma);
        return err;
}

static bool valid_arg_len(struct linux_binprm *bprm, long len)
{
        return len <= MAX_ARG_STRLEN;
}

#else

void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
{
}

struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
                int write)
{
        struct page *page;

        page = bprm->page[pos / PAGE_SIZE];
        if (!page && write) {
                page = alloc_page(GFP_HIGHUSER|__GFP_ZERO);
                if (!page)
                        return NULL;
                bprm->page[pos / PAGE_SIZE] = page;
        }

        return page;
}

static void put_arg_page(struct page *page)
{
}

static void free_arg_page(struct linux_binprm *bprm, int i)
{
        if (bprm->page[i]) {
                __free_page(bprm->page[i]);
                bprm->page[i] = NULL;
        }
}

static void free_arg_pages(struct linux_binprm *bprm)
{
        int i;

        for (i = 0; i < MAX_ARG_PAGES; i++)
                free_arg_page(bprm, i);
}

static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
                struct page *page)
{
}

static int __bprm_mm_init(struct linux_binprm *bprm)
{
        bprm->p = PAGE_SIZE * MAX_ARG_PAGES - sizeof(void *);
        return 0;
}

static bool valid_arg_len(struct linux_binprm *bprm, long len)
{
        return len <= bprm->p;
}

#endif /* CONFIG_MMU */

/*
 * Create a new mm_struct and populate it with a temporary stack
 * vm_area_struct.  We don't have enough context at this point to set the stack
 * flags, permissions, and offset, so we use temporary values.  We'll update
 * them later in setup_arg_pages().
 */
int bprm_mm_init(struct linux_binprm *bprm)
{
        int err;
        struct mm_struct *mm = NULL;

        bprm->mm = mm = mm_alloc();
        err = -ENOMEM;
        if (!mm)
                goto err;

        err = init_new_context(current, mm);
        if (err)
                goto err;

        err = __bprm_mm_init(bprm);
        if (err)
                goto err;

        return 0;

err:
        if (mm) {
                bprm->mm = NULL;
                mmdrop(mm);
        }

        return err;
}

/*
 * count() counts the number of strings in array ARGV.
 */
static int count(char __user * __user * argv, int max)
{
        int i = 0;

        if (argv != NULL) {
                for (;;) {
                        char __user * p;

                        if (get_user(p, argv))
                                return -EFAULT;
                        if (!p)
                                break;
                        argv++;
                        if (i++ >= max)
                                return -E2BIG;

                        if (fatal_signal_pending(current))
                                return -ERESTARTNOHAND;
                        cond_resched();
                }
        }
        return i;
}

/*
 * 'copy_strings()' copies argument/environment strings from the old
 * processes's memory to the new process's stack.  The call to get_user_pages()
 * ensures the destination page is created and not swapped out.
 */
static int copy_strings(int argc, char __user * __user * argv,
                        struct linux_binprm *bprm)
{
        struct page *kmapped_page = NULL;
        char *kaddr = NULL;
        unsigned long kpos = 0;
        int ret;

        while (argc-- > 0) {
                char __user *str;
                int len;
                unsigned long pos;

                if (get_user(str, argv+argc) ||
                                !(len = strnlen_user(str, MAX_ARG_STRLEN))) {
                        ret = -EFAULT;
                        goto out;
                }

                if (!valid_arg_len(bprm, len)) {
                        ret = -E2BIG;
                        goto out;
                }

                /* We're going to work our way backwords. */
                pos = bprm->p;
                str += len;
                bprm->p -= len;

                while (len > 0) {
                        int offset, bytes_to_copy;

                        if (fatal_signal_pending(current)) {
                                ret = -ERESTARTNOHAND;
                                goto out;
                        }
                        cond_resched();

                        offset = pos % PAGE_SIZE;
                        if (offset == 0)
                                offset = PAGE_SIZE;

                        bytes_to_copy = offset;
                        if (bytes_to_copy > len)
                                bytes_to_copy = len;

                        offset -= bytes_to_copy;
                        pos -= bytes_to_copy;
                        str -= bytes_to_copy;
                        len -= bytes_to_copy;

                        if (!kmapped_page || kpos != (pos & PAGE_MASK)) {
                                struct page *page;

                                page = get_arg_page(bprm, pos, 1);
                                if (!page) {
                                        ret = -E2BIG;
                                        goto out;
                                }

                                if (kmapped_page) {
                                        flush_kernel_dcache_page(kmapped_page);
                                        kunmap(kmapped_page);
                                        put_arg_page(kmapped_page);
                                }
                                kmapped_page = page;
                                kaddr = kmap(kmapped_page);
                                kpos = pos & PAGE_MASK;
                                flush_arg_page(bprm, kpos, kmapped_page);
                        }
                        if (copy_from_user(kaddr+offset, str, bytes_to_copy)) {
                                ret = -EFAULT;
                                goto out;
                        }
                }
        }
        ret = 0;
out:
        if (kmapped_page) {
                flush_kernel_dcache_page(kmapped_page);
                kunmap(kmapped_page);
                put_arg_page(kmapped_page);
        }
        return ret;
}

/*
 * Like copy_strings, but get argv and its values from kernel memory.
 */
int copy_strings_kernel(int argc,char ** argv, struct linux_binprm *bprm)
{
        int r;
        mm_segment_t oldfs = get_fs();
        set_fs(KERNEL_DS);
        r = copy_strings(argc, (char __user * __user *)argv, bprm);
        set_fs(oldfs);
        return r;
}
EXPORT_SYMBOL(copy_strings_kernel);

#ifdef CONFIG_MMU

/*
 * During bprm_mm_init(), we create a temporary stack at STACK_TOP_MAX.  Once
 * the binfmt code determines where the new stack should reside, we shift it to
 * its final location.  The process proceeds as follows:
 *
 * 1) Use shift to calculate the new vma endpoints.
 * 2) Extend vma to cover both the old and new ranges.  This ensures the
 *    arguments passed to subsequent functions are consistent.
 * 3) Move vma's page tables to the new range.
 * 4) Free up any cleared pgd range.
 * 5) Shrink the vma to cover only the new range.
 */
static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long old_start = vma->vm_start;
        unsigned long old_end = vma->vm_end;
        unsigned long length = old_end - old_start;
        unsigned long new_start = old_start - shift;
        unsigned long new_end = old_end - shift;
        struct mmu_gather *tlb;

        BUG_ON(new_start > new_end);

        /*
         * ensure there are no vmas between where we want to go
         * and where we are
         */
        if (vma != find_vma(mm, new_start))
                return -EFAULT;

        /*
         * cover the whole range: [new_start, old_end)
         */
        vma_adjust(vma, new_start, old_end, vma->vm_pgoff, NULL);

        /*
         * move the page tables downwards, on failure we rely on
         * process cleanup to remove whatever mess we made.
         */
        if (length != move_page_tables(vma, old_start,
                                       vma, new_start, length))
                return -ENOMEM;

        lru_add_drain();
        tlb = tlb_gather_mmu(mm, 0);
        if (new_end > old_start) {
                /*
                 * when the old and new regions overlap clear from new_end.
                 */
                free_pgd_range(tlb, new_end, old_end, new_end,
                        vma->vm_next ? vma->vm_next->vm_start : 0);
        } else {
                /*
                 * otherwise, clean from old_start; this is done to not touch
                 * the address space in [new_end, old_start) some architectures
                 * have constraints on va-space that make this illegal (IA64) -
                 * for the others its just a little faster.
                 */
                free_pgd_range(tlb, old_start, old_end, new_end,
                        vma->vm_next ? vma->vm_next->vm_start : 0);
        }
        tlb_finish_mmu(tlb, new_end, old_end);

        /*
         * shrink the vma to just the new range.
         */
        vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL);

        return 0;
}

#define EXTRA_STACK_VM_PAGES    20      /* random */

/*
 * Finalizes the stack vm_area_struct. The flags and permissions are updated,
 * the stack is optionally relocated, and some extra space is added.
 */
int setup_arg_pages(struct linux_binprm *bprm,
                    unsigned long stack_top,
                    int executable_stack)
{
        unsigned long ret;
        unsigned long stack_shift;
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma = bprm->vma;
        struct vm_area_struct *prev = NULL;
        unsigned long vm_flags;
        unsigned long stack_base;
        unsigned long stack_size;
        unsigned long stack_expand;
        unsigned long rlim_stack;

#ifdef CONFIG_STACK_GROWSUP
        /* Limit stack size to 1GB */
        stack_base = current->signal->rlim[RLIMIT_STACK].rlim_max;
        if (stack_base > (1 << 30))
                stack_base = 1 << 30;

        /* Make sure we didn't let the argument array grow too large. */
        if (vma->vm_end - vma->vm_start > stack_base)
                return -ENOMEM;

        stack_base = PAGE_ALIGN(stack_top - stack_base);

        stack_shift = vma->vm_start - stack_base;
        mm->arg_start = bprm->p - stack_shift;
        bprm->p = vma->vm_end - stack_shift;
#else
        stack_top = arch_align_stack(stack_top);
        stack_top = PAGE_ALIGN(stack_top);

        if (unlikely(stack_top < mmap_min_addr) ||
            unlikely(vma->vm_end - vma->vm_start >= stack_top - mmap_min_addr))
                return -ENOMEM;

        stack_shift = vma->vm_end - stack_top;

        bprm->p -= stack_shift;
        mm->arg_start = bprm->p;
#endif

        if (bprm->loader)
                bprm->loader -= stack_shift;
        bprm->exec -= stack_shift;

        down_write(&mm->mmap_sem);
        vm_flags = VM_STACK_FLAGS;

        /*
         * Adjust stack execute permissions; explicitly enable for
         * EXSTACK_ENABLE_X, disable for EXSTACK_DISABLE_X and leave alone
         * (arch default) otherwise.
         */
        if (unlikely(executable_stack == EXSTACK_ENABLE_X))
                vm_flags |= VM_EXEC;
        else if (executable_stack == EXSTACK_DISABLE_X)
                vm_flags &= ~VM_EXEC;
        vm_flags |= mm->def_flags;

        ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
                        vm_flags);
        if (ret)
                goto out_unlock;
        BUG_ON(prev != vma);

        /* Move stack pages down in memory. */
        if (stack_shift) {
                ret = shift_arg_pages(vma, stack_shift);
                if (ret)
                        goto out_unlock;
        }

        stack_expand = EXTRA_STACK_VM_PAGES * PAGE_SIZE;
        stack_size = vma->vm_end - vma->vm_start;
        /*
         * Align this down to a page boundary as expand_stack
         * will align it up.
         */
        rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
#ifdef CONFIG_STACK_GROWSUP
        if (stack_size + stack_expand > rlim_stack)
                stack_base = vma->vm_start + rlim_stack;
        else
                stack_base = vma->vm_end + stack_expand;
#else
        if (stack_size + stack_expand > rlim_stack)
                stack_base = vma->vm_end - rlim_stack;
        else
                stack_base = vma->vm_start - stack_expand;
#endif
        ret = expand_stack(vma, stack_base);
        if (ret)
                ret = -EFAULT;

out_unlock:
        up_write(&mm->mmap_sem);
        return ret;
}
EXPORT_SYMBOL(setup_arg_pages);

#endif /* CONFIG_MMU */

struct file *open_exec(const char *name)
{
        struct file *file;
        int err;

        file = do_filp_open(AT_FDCWD, name,
                                O_LARGEFILE | O_RDONLY | FMODE_EXEC, 0,
                                MAY_EXEC | MAY_OPEN);
        if (IS_ERR(file))
                goto out;

        err = -EACCES;
        if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
                goto exit;

        if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
                goto exit;

        fsnotify_open(file->f_path.dentry);

        err = deny_write_access(file);
        if (err)
                goto exit;

out:
        return file;

exit:
        fput(file);
        return ERR_PTR(err);
}
EXPORT_SYMBOL(open_exec);

int kernel_read(struct file *file, loff_t offset,
                char *addr, unsigned long count)
{
        mm_segment_t old_fs;
        loff_t pos = offset;
        int result;

        old_fs = get_fs();
        set_fs(get_ds());
        /* The cast to a user pointer is valid due to the set_fs() */
        result = vfs_read(file, (void __user *)addr, count, &pos);
        set_fs(old_fs);
        return result;
}

EXPORT_SYMBOL(kernel_read);

static int exec_mmap(struct mm_struct *mm)
{
        struct task_struct *tsk;
        struct mm_struct * old_mm, *active_mm;

        /* Notify parent that we're no longer interested in the old VM */
        tsk = current;
        old_mm = current->mm;
        mm_release(tsk, old_mm);

        if (old_mm) {
                /*
                 * Make sure that if there is a core dump in progress
                 * for the old mm, we get out and die instead of going
                 * through with the exec.  We must hold mmap_sem around
                 * checking core_state and changing tsk->mm.
                 */
                down_read(&old_mm->mmap_sem);
                if (unlikely(old_mm->core_state)) {
                        up_read(&old_mm->mmap_sem);
                        return -EINTR;
                }
        }
        task_lock(tsk);
        active_mm = tsk->active_mm;
        tsk->mm = mm;
        tsk->active_mm = mm;
        activate_mm(active_mm, mm);
        task_unlock(tsk);
        arch_pick_mmap_layout(mm);
        if (old_mm) {
                up_read(&old_mm->mmap_sem);
                BUG_ON(active_mm != old_mm);
                mm_update_next_owner(old_mm);
                mmput(old_mm);
                return 0;
        }
        mmdrop(active_mm);
        return 0;
}

/*
 * This function makes sure the current process has its own signal table,
 * so that flush_signal_handlers can later reset the handlers without
 * disturbing other processes.  (Other processes might share the signal
 * table via the CLONE_SIGHAND option to clone().)
 */
static int de_thread(struct task_struct *tsk)
{
        struct signal_struct *sig = tsk->signal;
        struct sighand_struct *oldsighand = tsk->sighand;
        spinlock_t *lock = &oldsighand->siglock;
        int count;

        if (thread_group_empty(tsk))
                goto no_thread_group;

        /*
         * Kill all other threads in the thread group.
         */
        spin_lock_irq(lock);
        if (signal_group_exit(sig)) {
                /*
                 * Another group action in progress, just
                 * return so that the signal is processed.
                 */
                spin_unlock_irq(lock);
                return -EAGAIN;
        }
        sig->group_exit_task = tsk;
        zap_other_threads(tsk);

        /* Account for the thread group leader hanging around: */
        count = thread_group_leader(tsk) ? 1 : 2;
        sig->notify_count = count;
        while (atomic_read(&sig->count) > count) {
                __set_current_state(TASK_UNINTERRUPTIBLE);
                spin_unlock_irq(lock);
                schedule();
                spin_lock_irq(lock);
        }
        spin_unlock_irq(lock);

        /*
         * At this point all other threads have exited, all we have to
         * do is to wait for the thread group leader to become inactive,
         * and to assume its PID:
         */
        if (!thread_group_leader(tsk)) {
                struct task_struct *leader = tsk->group_leader;

                sig->notify_count = -1; /* for exit_notify() */
                for (;;) {
                        write_lock_irq(&tasklist_lock);
                        if (likely(leader->exit_state))
                                break;
                        __set_current_state(TASK_UNINTERRUPTIBLE);
                        write_unlock_irq(&tasklist_lock);
                        schedule();
                }

                /*
                 * The only record we have of the real-time age of a
                 * process, regardless of execs it's done, is start_time.
                 * All the past CPU time is accumulated in signal_struct
                 * from sister threads now dead.  But in this non-leader
                 * exec, nothing survives from the original leader thread,
                 * whose birth marks the true age of this process now.
                 * When we take on its identity by switching to its PID, we
                 * also take its birthdate (always earlier than our own).
                 */
                tsk->start_time = leader->start_time;

                BUG_ON(!same_thread_group(leader, tsk));
                BUG_ON(has_group_leader_pid(tsk));
                /*
                 * An exec() starts a new thread group with the
                 * TGID of the previous thread group. Rehash the
                 * two threads with a switched PID, and release
                 * the former thread group leader:
                 */

                /* Become a process group leader with the old leader's pid.
                 * The old leader becomes a thread of the this thread group.
                 * Note: The old leader also uses this pid until release_task
                 *       is called.  Odd but simple and correct.
                 */
                detach_pid(tsk, PIDTYPE_PID);
                tsk->pid = leader->pid;
                attach_pid(tsk, PIDTYPE_PID,  task_pid(leader));
                transfer_pid(leader, tsk, PIDTYPE_PGID);
                transfer_pid(leader, tsk, PIDTYPE_SID);

                list_replace_rcu(&leader->tasks, &tsk->tasks);
                list_replace_init(&leader->sibling, &tsk->sibling);

                tsk->group_leader = tsk;
                leader->group_leader = tsk;

                tsk->exit_signal = SIGCHLD;

                BUG_ON(leader->exit_state != EXIT_ZOMBIE);
                leader->exit_state = EXIT_DEAD;
                write_unlock_irq(&tasklist_lock);

                release_task(leader);
        }

        sig->group_exit_task = NULL;
        sig->notify_count = 0;

no_thread_group:
        if (current->mm)
                setmax_mm_hiwater_rss(&sig->maxrss, current->mm);

        exit_itimers(sig);
        flush_itimer_signals();

        if (atomic_read(&oldsighand->count) != 1) {
                struct sighand_struct *newsighand;
                /*
                 * This ->sighand is shared with the CLONE_SIGHAND
                 * but not CLONE_THREAD task, switch to the new one.
                 */
                newsighand = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
                if (!newsighand)
                        return -ENOMEM;

                atomic_set(&newsighand->count, 1);
                memcpy(newsighand->action, oldsighand->action,
                       sizeof(newsighand->action));

                write_lock_irq(&tasklist_lock);
                spin_lock(&oldsighand->siglock);
                rcu_assign_pointer(tsk->sighand, newsighand);
                spin_unlock(&oldsighand->siglock);
                write_unlock_irq(&tasklist_lock);

                __cleanup_sighand(oldsighand);
        }

        BUG_ON(!thread_group_leader(tsk));
        return 0;
}

/*
 * These functions flushes out all traces of the currently running executable
 * so that a new one can be started
 */
static void flush_old_files(struct files_struct * files)
{
        long j = -1;
        struct fdtable *fdt;

        spin_lock(&files->file_lock);
        for (;;) {
                unsigned long set, i;

                j++;
                i = j * __NFDBITS;
                fdt = files_fdtable(files);
                if (i >= fdt->max_fds)
                        break;
                set = fdt->close_on_exec->fds_bits[j];
                if (!set)
                        continue;
                fdt->close_on_exec->fds_bits[j] = 0;
                spin_unlock(&files->file_lock);
                for ( ; set ; i++,set >>= 1) {
                        if (set & 1) {
                                sys_close(i);
                        }
                }
                spin_lock(&files->file_lock);

        }
        spin_unlock(&files->file_lock);
}

char *get_task_comm(char *buf, struct task_struct *tsk)
{
        /* buf must be at least sizeof(tsk->comm) in size */
        task_lock(tsk);
        strncpy(buf, tsk->comm, sizeof(tsk->comm));
        task_unlock(tsk);
        return buf;
}

void set_task_comm(struct task_struct *tsk, char *buf)
{
        task_lock(tsk);

        /*
         * Threads may access current->comm without holding
         * the task lock, so write the string carefully.
         * Readers without a lock may see incomplete new
         * names but are safe from non-terminating string reads.
         */
        memset(tsk->comm, 0, TASK_COMM_LEN);
        wmb();
        strlcpy(tsk->comm, buf, sizeof(tsk->comm));
        task_unlock(tsk);
        perf_event_comm(tsk);
}

int flush_old_exec(struct linux_binprm * bprm)
{
        int retval;

        /*
         * Make sure we have a private signal table and that
         * we are unassociated from the previous thread group.
         */
        retval = de_thread(current);
        if (retval)
                goto out;

        set_mm_exe_file(bprm->mm, bprm->file);

        /*
         * Release all of the old mmap stuff
         */
        acct_arg_size(bprm, 0);
        retval = exec_mmap(bprm->mm);
        if (retval)
                goto out;

        bprm->mm = NULL;                /* We're using it now */

        current->flags &= ~PF_RANDOMIZE;
        flush_thread();
        current->personality &= ~bprm->per_clear;

        return 0;

out:
        return retval;
}
EXPORT_SYMBOL(flush_old_exec);

void setup_new_exec(struct linux_binprm * bprm)
{
        int i, ch;
        char * name;
        char tcomm[sizeof(current->comm)];

        arch_pick_mmap_layout(current->mm);

        /* This is the point of no return */
        current->sas_ss_sp = current->sas_ss_size = 0;

        if (current_euid() == current_uid() && current_egid() == current_gid())
                set_dumpable(current->mm, 1);
        else
                set_dumpable(current->mm, suid_dumpable);

        name = bprm->filename;

        /* Copies the binary name from after last slash */
        for (i=0; (ch = *(name++)) != '\0';) {
                if (ch == '/')
                        i = 0; /* overwrite what we wrote */
                else
                        if (i < (sizeof(tcomm) - 1))
                                tcomm[i++] = ch;
        }
        tcomm[i] = '\0';
        set_task_comm(current, tcomm);

        /* Set the new mm task size. We have to do that late because it may
         * depend on TIF_32BIT which is only updated in flush_thread() on
         * some architectures like powerpc
         */
        current->mm->task_size = TASK_SIZE;

        /* install the new credentials */
        if (bprm->cred->uid != current_euid() ||
            bprm->cred->gid != current_egid()) {
                current->pdeath_signal = 0;
        } else if (file_permission(bprm->file, MAY_READ) ||
                   bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP) {
                set_dumpable(current->mm, suid_dumpable);
        }

        /*
         * Flush performance counters when crossing a
         * security domain:
         */
        if (!get_dumpable(current->mm))
                perf_event_exit_task(current);

        /* An exec changes our domain. We are no longer part of the thread
           group */

        current->self_exec_id++;
                        
        flush_signal_handlers(current, 0);
        flush_old_files(current->files);
}
EXPORT_SYMBOL(setup_new_exec);

/*
 * Prepare credentials and lock ->cred_guard_mutex.
 * install_exec_creds() commits the new creds and drops the lock.
 * Or, if exec fails before, free_bprm() should release ->cred and
 * and unlock.
 */
int prepare_bprm_creds(struct linux_binprm *bprm)
{
        if (mutex_lock_interruptible(&current->cred_guard_mutex))
                return -ERESTARTNOINTR;

        bprm->cred = prepare_exec_creds();
        if (likely(bprm->cred))
                return 0;

        mutex_unlock(&current->cred_guard_mutex);
        return -ENOMEM;
}

void free_bprm(struct linux_binprm *bprm)
{
        free_arg_pages(bprm);
        if (bprm->cred) {
                mutex_unlock(&current->cred_guard_mutex);
                abort_creds(bprm->cred);
        }
        kfree(bprm);
}

/*
 * install the new credentials for this executable
 */
void install_exec_creds(struct linux_binprm *bprm)
{
        security_bprm_committing_creds(bprm);

        commit_creds(bprm->cred);
        bprm->cred = NULL;
        /*
         * cred_guard_mutex must be held at least to this point to prevent
         * ptrace_attach() from altering our determination of the task's
         * credentials; any time after this it may be unlocked.
         */
        security_bprm_committed_creds(bprm);
        mutex_unlock(&current->cred_guard_mutex);
}
EXPORT_SYMBOL(install_exec_creds);

/*
 * determine how safe it is to execute the proposed program
 * - the caller must hold current->cred_guard_mutex to protect against
 *   PTRACE_ATTACH
 */
int check_unsafe_exec(struct linux_binprm *bprm)
{
        struct task_struct *p = current, *t;
        unsigned n_fs;
        int res = 0;

        bprm->unsafe = tracehook_unsafe_exec(p);

        n_fs = 1;
        write_lock(&p->fs->lock);
        rcu_read_lock();
        for (t = next_thread(p); t != p; t = next_thread(t)) {
                if (t->fs == p->fs)
                        n_fs++;
        }
        rcu_read_unlock();

        if (p->fs->users > n_fs) {
                bprm->unsafe |= LSM_UNSAFE_SHARE;
        } else {
                res = -EAGAIN;
                if (!p->fs->in_exec) {
                        p->fs->in_exec = 1;
                        res = 1;
                }
        }
        write_unlock(&p->fs->lock);

        return res;
}

/* 
 * Fill the binprm structure from the inode. 
 * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
 *
 * This may be called multiple times for binary chains (scripts for example).
 */
int prepare_binprm(struct linux_binprm *bprm)
{
        umode_t mode;
        struct inode * inode = bprm->file->f_path.dentry->d_inode;
        int retval;

        mode = inode->i_mode;
        if (bprm->file->f_op == NULL)
                return -EACCES;

        /* clear any previous set[ug]id data from a previous binary */
        bprm->cred->euid = current_euid();
        bprm->cred->egid = current_egid();

        if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)) {
                /* Set-uid? */
                if (mode & S_ISUID) {
                        bprm->per_clear |= PER_CLEAR_ON_SETID;
                        bprm->cred->euid = inode->i_uid;
                }

                /* Set-gid? */
                /*
                 * If setgid is set but no group execute bit then this
                 * is a candidate for mandatory locking, not a setgid
                 * executable.
                 */
                if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
                        bprm->per_clear |= PER_CLEAR_ON_SETID;
                        bprm->cred->egid = inode->i_gid;
                }
        }

        /* fill in binprm security blob */
        retval = security_bprm_set_creds(bprm);
        if (retval)
                return retval;
        bprm->cred_prepared = 1;

        memset(bprm->buf, 0, BINPRM_BUF_SIZE);
        return kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
}

EXPORT_SYMBOL(prepare_binprm);

/*
 * Arguments are '\0' separated strings found at the location bprm->p
 * points to; chop off the first by relocating brpm->p to right after
 * the first '\0' encountered.
 */
int remove_arg_zero(struct linux_binprm *bprm)
{
        int ret = 0;
        unsigned long offset;
        char *kaddr;
        struct page *page;

        if (!bprm->argc)
                return 0;

        do {
                offset = bprm->p & ~PAGE_MASK;
                page = get_arg_page(bprm, bprm->p, 0);
                if (!page) {
                        ret = -EFAULT;
                        goto out;
                }
                kaddr = kmap_atomic(page, KM_USER0);

                for (; offset < PAGE_SIZE && kaddr[offset];
                                offset++, bprm->p++)
                        ;

                kunmap_atomic(kaddr, KM_USER0);
                put_arg_page(page);

                if (offset == PAGE_SIZE)
                        free_arg_page(bprm, (bprm->p >> PAGE_SHIFT) - 1);
        } while (offset == PAGE_SIZE);

        bprm->p++;
        bprm->argc--;
        ret = 0;

out:
        return ret;
}
EXPORT_SYMBOL(remove_arg_zero);

/*
 * cycle the list of binary formats handler, until one recognizes the image
 */
int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
{
        unsigned int depth = bprm->recursion_depth;
        int try,retval;
        struct linux_binfmt *fmt;

        retval = security_bprm_check(bprm);
        if (retval)
                return retval;

        /* kernel module loader fixup */
        /* so we don't try to load run modprobe in kernel space. */
        set_fs(USER_DS);

        retval = audit_bprm(bprm);
        if (retval)
                return retval;

        retval = -ENOENT;
        for (try=0; try<2; try++) {
                read_lock(&binfmt_lock);
                list_for_each_entry(fmt, &formats, lh) {
                        int (*fn)(struct linux_binprm *, struct pt_regs *) = fmt->load_binary;
                        if (!fn)
                                continue;
                        if (!try_module_get(fmt->module))
                                continue;
                        read_unlock(&binfmt_lock);
                        retval = fn(bprm, regs);
                        /*
                         * Restore the depth counter to its starting value
                         * in this call, so we don't have to rely on every
                         * load_binary function to restore it on return.
                         */
                        bprm->recursion_depth = depth;
                        if (retval >= 0) {
                                if (depth == 0)
                                        tracehook_report_exec(fmt, bprm, regs);
                                put_binfmt(fmt);
                                allow_write_access(bprm->file);
                                if (bprm->file)
                                        fput(bprm->file);
                                bprm->file = NULL;
                                current->did_exec = 1;
                                proc_exec_connector(current);
                                return retval;
                        }
                        read_lock(&binfmt_lock);
                        put_binfmt(fmt);
                        if (retval != -ENOEXEC || bprm->mm == NULL)
                                break;
                        if (!bprm->file) {
                                read_unlock(&binfmt_lock);
                                return retval;
                        }
                }
                read_unlock(&binfmt_lock);
                if (retval != -ENOEXEC || bprm->mm == NULL) {
                        break;
#ifdef CONFIG_MODULES
                } else {
#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
                        if (printable(bprm->buf[0]) &&
                            printable(bprm->buf[1]) &&
                            printable(bprm->buf[2]) &&
                            printable(bprm->buf[3]))
                                break; /* -ENOEXEC */
                        request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
#endif
                }
        }
        return retval;
}

EXPORT_SYMBOL(search_binary_handler);

/*
 * sys_execve() executes a new program.
 */
int do_execve(char * filename,
        char __user *__user *argv,
        char __user *__user *envp,
        struct pt_regs * regs)
{
        struct linux_binprm *bprm;
        struct file *file;
        struct files_struct *displaced;
        bool clear_in_exec;
        int retval;

        retval = unshare_files(&displaced);
        if (retval)
                goto out_ret;

        retval = -ENOMEM;
        bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
        if (!bprm)
                goto out_files;

        retval = prepare_bprm_creds(bprm);
        if (retval)
                goto out_free;

        retval = check_unsafe_exec(bprm);
        if (retval < 0)
                goto out_free;
        clear_in_exec = retval;
        current->in_execve = 1;

        file = open_exec(filename);
        retval = PTR_ERR(file);
        if (IS_ERR(file))
                goto out_unmark;

        sched_exec();

        bprm->file = file;
        bprm->filename = filename;
        bprm->interp = filename;

        retval = bprm_mm_init(bprm);
        if (retval)
                goto out_file;

        bprm->argc = count(argv, MAX_ARG_STRINGS);
        if ((retval = bprm->argc) < 0)
                goto out;

        bprm->envc = count(envp, MAX_ARG_STRINGS);
        if ((retval = bprm->envc) < 0)
                goto out;

        retval = prepare_binprm(bprm);
        if (retval < 0)
                goto out;

        retval = copy_strings_kernel(1, &bprm->filename, bprm);
        if (retval < 0)
                goto out;

        bprm->exec = bprm->p;
        retval = copy_strings(bprm->envc, envp, bprm);
        if (retval < 0)
                goto out;

        retval = copy_strings(bprm->argc, argv, bprm);
        if (retval < 0)
                goto out;

        current->flags &= ~PF_KTHREAD;
        retval = search_binary_handler(bprm,regs);
        if (retval < 0)
                goto out;

        /* execve succeeded */
        current->fs->in_exec = 0;
        current->in_execve = 0;
        acct_update_integrals(current);
        free_bprm(bprm);
        if (displaced)
                put_files_struct(displaced);
        return retval;

out:
        if (bprm->mm) {
                acct_arg_size(bprm, 0);
                mmput(bprm->mm);
        }

out_file:
        if (bprm->file) {
                allow_write_access(bprm->file);
                fput(bprm->file);
        }

out_unmark:
        if (clear_in_exec)
                current->fs->in_exec = 0;
        current->in_execve = 0;

out_free:
        free_bprm(bprm);

out_files:
        if (displaced)
                reset_files_struct(displaced);
out_ret:
        return retval;
}

void set_binfmt(struct linux_binfmt *new)
{
        struct mm_struct *mm = current->mm;

        if (mm->binfmt)
                module_put(mm->binfmt->module);

        mm->binfmt = new;
        if (new)
                __module_get(new->module);
}

EXPORT_SYMBOL(set_binfmt);

/* format_corename will inspect the pattern parameter, and output a
 * name into corename, which must have space for at least
 * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
 */
static int format_corename(char *corename, long signr)
{
        const struct cred *cred = current_cred();
        const char *pat_ptr = core_pattern;
        int ispipe = (*pat_ptr == '|');
        char *out_ptr = corename;
        char *const out_end = corename + CORENAME_MAX_SIZE;
        int rc;
        int pid_in_pattern = 0;

        /* Repeat as long as we have more pattern to process and more output
           space */
        while (*pat_ptr) {
                if (*pat_ptr != '%') {
                        if (out_ptr == out_end)
                                goto out;
                        *out_ptr++ = *pat_ptr++;
                } else {
                        switch (*++pat_ptr) {
                        case 0:
                                goto out;
                        /* Double percent, output one percent */
                        case '%':
                                if (out_ptr == out_end)
                                        goto out;
                                *out_ptr++ = '%';
                                break;
                        /* pid */
                        case 'p':
                                pid_in_pattern = 1;
                                rc = snprintf(out_ptr, out_end - out_ptr,
                                              "%d", task_tgid_vnr(current));
                                if (rc > out_end - out_ptr)
                                        goto out;
                                out_ptr += rc;
                                break;
                        /* uid */
                        case 'u':
                                rc = snprintf(out_ptr, out_end - out_ptr,
                                              "%d", cred->uid);
                                if (rc > out_end - out_ptr)
                                        goto out;
                                out_ptr += rc;
                                break;
                        /* gid */
                        case 'g':
                                rc = snprintf(out_ptr, out_end - out_ptr,
                                              "%d", cred->gid);
                                if (rc > out_end - out_ptr)
                                        goto out;
                                out_ptr += rc;
                                break;
                        /* signal that caused the coredump */
                        case 's':
                                rc = snprintf(out_ptr, out_end - out_ptr,
                                              "%ld", signr);
                                if (rc > out_end - out_ptr)
                                        goto out;
                                out_ptr += rc;
                                break;
                        /* UNIX time of coredump */
                        case 't': {
                                struct timeval tv;
                                do_gettimeofday(&tv);
                                rc = snprintf(out_ptr, out_end - out_ptr,
                                              "%lu", tv.tv_sec);
                                if (rc > out_end - out_ptr)
                                        goto out;
                                out_ptr += rc;
                                break;
                        }
                        /* hostname */
                        case 'h':
                                down_read(&uts_sem);
                                rc = snprintf(out_ptr, out_end - out_ptr,
                                              "%s", utsname()->nodename);
                                up_read(&uts_sem);
                                if (rc > out_end - out_ptr)
                                        goto out;
                                out_ptr += rc;
                                break;
                        /* executable */
                        case 'e':
                                rc = snprintf(out_ptr, out_end - out_ptr,
                                              "%s", current->comm);
                                if (rc > out_end - out_ptr)
                                        goto out;
                                out_ptr += rc;
                                break;
                        /* core limit size */
                        case 'c':
                                rc = snprintf(out_ptr, out_end - out_ptr,
                                              "%lu", current->signal->rlim[RLIMIT_CORE].rlim_cur);
                                if (rc > out_end - out_ptr)
                                        goto out;
                                out_ptr += rc;
                                break;
                        default:
                                break;
                        }
                        ++pat_ptr;
                }
        }
        /* Backward compatibility with core_uses_pid:
         *
         * If core_pattern does not include a %p (as is the default)
         * and core_uses_pid is set, then .%pid will be appended to
         * the filename. Do not do this for piped commands. */
        if (!ispipe && !pid_in_pattern && core_uses_pid) {
                rc = snprintf(out_ptr, out_end - out_ptr,
                              ".%d", task_tgid_vnr(current));
                if (rc > out_end - out_ptr)
                        goto out;
                out_ptr += rc;
        }
out:
        *out_ptr = 0;
        return ispipe;
}

static int zap_process(struct task_struct *start)
{
        struct task_struct *t;
        int nr = 0;

        start->signal->flags = SIGNAL_GROUP_EXIT;
        start->signal->group_stop_count = 0;

        t = start;
        do {
                if (t != current && t->mm) {
                        sigaddset(&t->pending.signal, SIGKILL);
                        signal_wake_up(t, 1);
                        nr++;
                }
        } while_each_thread(start, t);

        return nr;
}

static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
                                struct core_state *core_state, int exit_code)
{
        struct task_struct *g, *p;
        unsigned long flags;
        int nr = -EAGAIN;

        spin_lock_irq(&tsk->sighand->siglock);
        if (!signal_group_exit(tsk->signal)) {
                mm->core_state = core_state;
                tsk->signal->group_exit_code = exit_code;
                nr = zap_process(tsk);
        }
        spin_unlock_irq(&tsk->sighand->siglock);
        if (unlikely(nr < 0))
                return nr;

        if (atomic_read(&mm->mm_users) == nr + 1)
                goto done;
        /*
         * We should find and kill all tasks which use this mm, and we should
         * count them correctly into ->nr_threads. We don't take tasklist
         * lock, but this is safe wrt:
         *
         * fork:
         *      None of sub-threads can fork after zap_process(leader). All
         *      processes which were created before this point should be
         *      visible to zap_threads() because copy_process() adds the new
         *      process to the tail of init_task.tasks list, and lock/unlock
         *      of ->siglock provides a memory barrier.
         *
         * do_exit:
         *      The caller holds mm->mmap_sem. This means that the task which
         *      uses this mm can't pass exit_mm(), so it can't exit or clear
         *      its ->mm.
         *
         * de_thread:
         *      It does list_replace_rcu(&leader->tasks, &current->tasks),
         *      we must see either old or new leader, this does not matter.
         *      However, it can change p->sighand, so lock_task_sighand(p)
         *      must be used. Since p->mm != NULL and we hold ->mmap_sem
         *      it can't fail.
         *
         *      Note also that "g" can be the old leader with ->mm == NULL
         *      and already unhashed and thus removed from ->thread_group.
         *      This is OK, __unhash_process()->list_del_rcu() does not
         *      clear the ->next pointer, we will find the new leader via
         *      next_thread().
         */
        rcu_read_lock();
        for_each_process(g) {
                if (g == tsk->group_leader)
                        continue;
                if (g->flags & PF_KTHREAD)
                        continue;
                p = g;
                do {
                        if (p->mm) {
                                if (unlikely(p->mm == mm)) {
                                        lock_task_sighand(p, &flags);
                                        nr += zap_process(p);
                                        unlock_task_sighand(p, &flags);
                                }
                                break;
                        }
                } while_each_thread(g, p);
        }
        rcu_read_unlock();
done:
        atomic_set(&core_state->nr_threads, nr);
        return nr;
}

static int coredump_wait(int exit_code, struct core_state *core_state)
{
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->mm;
        struct completion *vfork_done;
        int core_waiters;

        init_completion(&core_state->startup);
        core_state->dumper.task = tsk;
        core_state->dumper.next = NULL;
        core_waiters = zap_threads(tsk, mm, core_state, exit_code);
        up_write(&mm->mmap_sem);

        if (unlikely(core_waiters < 0))
                goto fail;

        /*
         * Make sure nobody is waiting for us to release the VM,
         * otherwise we can deadlock when we wait on each other
         */
        vfork_done = tsk->vfork_done;
        if (vfork_done) {
                tsk->vfork_done = NULL;
                complete(vfork_done);
        }

        if (core_waiters)
                wait_for_completion(&core_state->startup);
fail:
        return core_waiters;
}

static void coredump_finish(struct mm_struct *mm)
{
        struct core_thread *curr, *next;
        struct task_struct *task;

        next = mm->core_state->dumper.next;
        while ((curr = next) != NULL) {
                next = curr->next;
                task = curr->task;
                /*
                 * see exit_mm(), curr->task must not see
                 * ->task == NULL before we read ->next.
                 */
                smp_mb();
                curr->task = NULL;
                wake_up_process(task);
        }

        mm->core_state = NULL;
}

/*
 * set_dumpable converts traditional three-value dumpable to two flags and
 * stores them into mm->flags.  It modifies lower two bits of mm->flags, but
 * these bits are not changed atomically.  So get_dumpable can observe the
 * intermediate state.  To avoid doing unexpected behavior, get get_dumpable
 * return either old dumpable or new one by paying attention to the order of
 * modifying the bits.
 *
 * dumpable |   mm->flags (binary)
 * old  new | initial interim  final
 * ---------+-----------------------
 *  0    1  |   00      01      01
 *  0    2  |   00      10(*)   11
 *  1    0  |   01      00      00
 *  1    2  |   01      11      11
 *  2    0  |   11      10(*)   00
 *  2    1  |   11      11      01
 *
 * (*) get_dumpable regards interim value of 10 as 11.
 */
void set_dumpable(struct mm_struct *mm, int value)
{
        switch (value) {
        case 0:
                clear_bit(MMF_DUMPABLE, &mm->flags);
                smp_wmb();
                clear_bit(MMF_DUMP_SECURELY, &mm->flags);
                break;
        case 1:
                set_bit(MMF_DUMPABLE, &mm->flags);
                smp_wmb();
                clear_bit(MMF_DUMP_SECURELY, &mm->flags);
                break;
        case 2:
                set_bit(MMF_DUMP_SECURELY, &mm->flags);
                smp_wmb();
                set_bit(MMF_DUMPABLE, &mm->flags);
                break;
        }
}

int get_dumpable(struct mm_struct *mm)
{
        int ret;

        ret = mm->flags & 0x3;
        return (ret >= 2) ? 2 : ret;
}

static void wait_for_dump_helpers(struct file *file)
{
        struct pipe_inode_info *pipe;

        pipe = file->f_path.dentry->d_inode->i_pipe;

        pipe_lock(pipe);
        pipe->readers++;
        pipe->writers--;

        while ((pipe->readers > 1) && (!signal_pending(current))) {
                wake_up_interruptible_sync(&pipe->wait);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                pipe_wait(pipe);
        }

        pipe->readers--;
        pipe->writers++;
        pipe_unlock(pipe);

}


void do_coredump(long signr, int exit_code, struct pt_regs *regs)
{
        struct core_state core_state;
        char corename[CORENAME_MAX_SIZE + 1];
        struct mm_struct *mm = current->mm;
        struct linux_binfmt * binfmt;
        struct inode * inode;
        const struct cred *old_cred;
        struct cred *cred;
        int retval = 0;
        int flag = 0;
        int ispipe = 0;
        char **helper_argv = NULL;
        int helper_argc = 0;
        int dump_count = 0;
        static atomic_t core_dump_count = ATOMIC_INIT(0);
        struct coredump_params cprm = {
                .signr = signr,
                .regs = regs,
                .limit = current->signal->rlim[RLIMIT_CORE].rlim_cur,
        };

        audit_core_dumps(signr);

        binfmt = mm->binfmt;
        if (!binfmt || !binfmt->core_dump)
                goto fail;

        cred = prepare_creds();
        if (!cred) {
                retval = -ENOMEM;
                goto fail;
        }

        down_write(&mm->mmap_sem);
        /*
         * If another thread got here first, or we are not dumpable, bail out.
         */
        if (mm->core_state || !get_dumpable(mm)) {
                up_write(&mm->mmap_sem);
                put_cred(cred);
                goto fail;
        }

        /*
         *      We cannot trust fsuid as being the "true" uid of the
         *      process nor do we know its entire history. We only know it
         *      was tainted so we dump it as root in mode 2.
         */
        if (get_dumpable(mm) == 2) {    /* Setuid core dump mode */
                flag = O_EXCL;          /* Stop rewrite attacks */
                cred->fsuid = 0;        /* Dump root private */
        }

        retval = coredump_wait(exit_code, &core_state);
        if (retval < 0) {
                put_cred(cred);
                goto fail;
        }

        old_cred = override_creds(cred);

        /*
         * Clear any false indication of pending signals that might
         * be seen by the filesystem code called to write the core file.
         */
        clear_thread_flag(TIF_SIGPENDING);

        /*
         * lock_kernel() because format_corename() is controlled by sysctl, which
         * uses lock_kernel()
         */
        lock_kernel();
        ispipe = format_corename(corename, signr);
        unlock_kernel();

        if ((!ispipe) && (cprm.limit < binfmt->min_coredump))
                goto fail_unlock;

        if (ispipe) {
                if (cprm.limit == 0) {
                        /*
                         * Normally core limits are irrelevant to pipes, since
                         * we're not writing to the file system, but we use
                         * cprm.limit of 0 here as a speacial value. Any
                         * non-zero limit gets set to RLIM_INFINITY below, but
                         * a limit of 0 skips the dump.  This is a consistent
                         * way to catch recursive crashes.  We can still crash
                         * if the core_pattern binary sets RLIM_CORE =  !0
                         * but it runs as root, and can do lots of stupid things
                         * Note that we use task_tgid_vnr here to grab the pid
                         * of the process group leader.  That way we get the
                         * right pid if a thread in a multi-threaded
                         * core_pattern process dies.
                         */
                        printk(KERN_WARNING
                                "Process %d(%s) has RLIMIT_CORE set to 0\n",
                                task_tgid_vnr(current), current->comm);
                        printk(KERN_WARNING "Aborting core\n");
                        goto fail_unlock;
                }

                dump_count = atomic_inc_return(&core_dump_count);
                if (core_pipe_limit && (core_pipe_limit < dump_count)) {
                        printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
                               task_tgid_vnr(current), current->comm);
                        printk(KERN_WARNING "Skipping core dump\n");
                        goto fail_dropcount;
                }

                helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc);
                if (!helper_argv) {
                        printk(KERN_WARNING "%s failed to allocate memory\n",
                               __func__);
                        goto fail_dropcount;
                }

                cprm.limit = RLIM_INFINITY;

                /* SIGPIPE can happen, but it's just never processed */
                if (call_usermodehelper_pipe(helper_argv[0], helper_argv, NULL,
                                &cprm.file)) {
                        printk(KERN_INFO "Core dump to %s pipe failed\n",
                               corename);
                        goto fail_dropcount;
                }
        } else
                cprm.file = filp_open(corename,
                                 O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
                                 0600);
        if (IS_ERR(cprm.file))
                goto fail_dropcount;
        inode = cprm.file->f_path.dentry->d_inode;
        if (inode->i_nlink > 1)
                goto close_fail;        /* multiple links - don't dump */
        if (!ispipe && d_unhashed(cprm.file->f_path.dentry))
                goto close_fail;

        /* AK: actually i see no reason to not allow this for named pipes etc.,
           but keep the previous behaviour for now. */
        if (!ispipe && !S_ISREG(inode->i_mode))
                goto close_fail;
        /*
         * Dont allow local users get cute and trick others to coredump
         * into their pre-created files:
         * Note, this is not relevant for pipes
         */
        if (!ispipe && (inode->i_uid != current_fsuid()))
                goto close_fail;
        if (!cprm.file->f_op)
                goto close_fail;
        if (!cprm.file->f_op->write)
                goto close_fail;
        if (!ispipe &&
            do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file) != 0)
                goto close_fail;

        retval = binfmt->core_dump(&cprm);

        if (retval)
                current->signal->group_exit_code |= 0x80;
close_fail:
        if (ispipe && core_pipe_limit)
                wait_for_dump_helpers(cprm.file);
        filp_close(cprm.file, NULL);
fail_dropcount:
        if (dump_count)
                atomic_dec(&core_dump_count);
fail_unlock:
        if (helper_argv)
                argv_free(helper_argv);

        revert_creds(old_cred);
        put_cred(cred);
        coredump_finish(mm);
fail:
        return;
}