kernel/kmod.c

   1 /*
   2         kmod, the new module loader (replaces kerneld)
   3         Kirk Petersen
   4
   5         Reorganized not to be a daemon by Adam Richter, with guidance
   6         from Greg Zornetzer.
   7
   8         Modified to avoid chroot and file sharing problems.
   9         Mikael Pettersson
  10
  11         Limit the concurrent number of kmod modprobes to catch loops from
  12         "modprobe needs a service that is in a module".
  13         Keith Owens <kaos@ocs.com.au> December 1999
  14 */
  15
  16 #define __KERNEL_SYSCALLS__
  17
  18 #include <linux/sched.h>
  19 #include <linux/unistd.h>
  20 #include <linux/smp_lock.h>
  21
  22 #include <asm/uaccess.h>
  23
  24 /*
  25         modprobe_path is set via /proc/sys.
  26 */
  27 char modprobe_path[256] = "/sbin/modprobe";
  28
  29 extern int max_threads;
  30
  31 static inline void
  32 use_init_fs_context(void)
  33 {
  34         struct fs_struct *our_fs, *init_fs;
  35         struct dentry *root, *pwd;
  36         struct vfsmount *rootmnt, *pwdmnt;
  37
  38         /*
  39          * Make modprobe's fs context be a copy of init's.
  40          *
  41          * We cannot use the user's fs context, because it
  42          * may have a different root than init.
  43          * Since init was created with CLONE_FS, we can grab
  44          * its fs context from "init_task".
  45          *
  46          * The fs context has to be a copy. If it is shared
  47          * with init, then any chdir() call in modprobe will
  48          * also affect init and the other threads sharing
  49          * init_task's fs context.
  50          *
  51          * We created the exec_modprobe thread without CLONE_FS,
  52          * so we can update the fields in our fs context freely.
  53          */
  54
  55         init_fs = init_task.fs;
  56         read_lock(&init_fs->lock);
  57         rootmnt = mntget(init_fs->rootmnt);
  58         root = dget(init_fs->root);
  59         pwdmnt = mntget(init_fs->pwdmnt);
  60         pwd = dget(init_fs->pwd);
  61         read_unlock(&init_fs->lock);
  62
  63         /* FIXME - unsafe ->fs access */
  64         our_fs = current->fs;
  65         our_fs->umask = init_fs->umask;
  66         set_fs_root(our_fs, rootmnt, root);
  67         set_fs_pwd(our_fs, pwdmnt, pwd);
  68         write_lock(&our_fs->lock);
  69         if (our_fs->altroot) {
  70                 struct vfsmount *mnt = our_fs->altrootmnt;
  71                 struct dentry *dentry = our_fs->altroot;
  72                 our_fs->altrootmnt = NULL;
  73                 our_fs->altroot = NULL;
  74                 write_unlock(&our_fs->lock);
  75                 dput(dentry);
  76                 mntput(mnt);
  77         } else
  78                 write_unlock(&our_fs->lock);
  79         dput(root);
  80         mntput(rootmnt);
  81         dput(pwd);
  82         mntput(pwdmnt);
  83 }
  84
  85 int exec_usermodehelper(char *program_path, char *argv[], char *envp[])
  86 {
  87         int i;
  88
  89         current->session = 1;
  90         current->pgrp = 1;
  91
  92         use_init_fs_context();
  93
  94         /* Prevent parent user process from sending signals to child.
  95            Otherwise, if the modprobe program does not exist, it might
  96            be possible to get a user defined signal handler to execute
  97            as the super user right after the execve fails if you time
  98            the signal just right.
  99         */
 100         spin_lock_irq(&current->sigmask_lock);
 101         flush_signals(current);
 102         flush_signal_handlers(current);
 103         spin_unlock_irq(&current->sigmask_lock);
 104
 105         for (i = 0; i < current->files->max_fds; i++ ) {
 106                 if (current->files->fd[i]) close(i);
 107         }
 108
 109         /* Drop the "current user" thing */
 110         free_uid(current);
 111
 112         /* Give kmod all effective privileges.. */
 113         current->uid = current->euid = current->fsuid = 0;
 114         cap_set_full(current->cap_effective);
 115
 116         /* Allow execve args to be in kernel space. */
 117         set_fs(KERNEL_DS);
 118
 119         /* Go, go, go... */
 120         if (execve(program_path, argv, envp) < 0)
 121                 return -errno;
 122         return 0;
 123 }
 124
 125 static int exec_modprobe(void * module_name)
 126 {
 127         static char * envp[] = { "HOME=/", "TERM=linux", "PATH=/sbin:/usr/sbin:/bin:/usr/bin", NULL };
 128         char *argv[] = { modprobe_path, "-s", "-k", (char*)module_name, NULL };
 129         int ret;
 130
 131         ret = exec_usermodehelper(modprobe_path, argv, envp);
 132         if (ret) {
 133                 printk(KERN_ERR
 134                        "kmod: failed to exec %s -s -k %s, errno = %d\n",
 135                        modprobe_path, (char*) module_name, errno);
 136         }
 137         return ret;
 138 }
 139
 140 /**
 141  *      request_module - try to load a kernel module
 142  *      @module_name: Name of module
 143  *
 144  *      Load a module using the user mode module loader. The function returns
 145  *      zero on success or a negative errno code on failure. Note that a
 146  *      successful module load does not mean the module did not then unload
 147  *      and exit on an error of its own. Callers must check that the service
 148  *      they requested is now available not blindly invoke it.
 149  *
 150  *      If module auto-loading support is disabled then this function
 151  *      becomes a no-operation.
 152  */
 153
 154 int request_module(const char * module_name)
 155 {
 156         int pid;
 157         int waitpid_result;
 158         sigset_t tmpsig;
 159         int i;
 160         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
 161 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
 162         static int kmod_loop_msg;
 163
 164         /* Don't allow request_module() before the root fs is mounted!  */
 165         if ( ! current->fs->root ) {
 166                 printk(KERN_ERR "request_module[%s]: Root fs not mounted\n",
 167                         module_name);
 168                 return -EPERM;
 169         }
 170
 171         /* If modprobe needs a service that is in a module, we get a recursive
 172          * loop.  Limit the number of running kmod threads to max_threads/2 or
 173          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
 174          * would be to run the parents of this process, counting how many times
 175          * kmod was invoked.  That would mean accessing the internals of the
 176          * process tables to get the command line, proc_pid_cmdline is static
 177          * and it is not worth changing the proc code just to handle this case.
 178          * KAO.
 179          */
 180         i = max_threads/2;
 181         if (i > MAX_KMOD_CONCURRENT)
 182                 i = MAX_KMOD_CONCURRENT;
 183         atomic_inc(&kmod_concurrent);
 184         if (atomic_read(&kmod_concurrent) > i) {
 185                 if (kmod_loop_msg++ < 5)
 186                         printk(KERN_ERR
 187                                "kmod: runaway modprobe loop assumed and stopped\n");
 188                 atomic_dec(&kmod_concurrent);
 189                 return -ENOMEM;
 190         }
 191
 192         pid = kernel_thread(exec_modprobe, (void*) module_name, 0);
 193         if (pid < 0) {
 194                 printk(KERN_ERR "request_module[%s]: fork failed, errno %d\n", module_name, -pid);
 195                 atomic_dec(&kmod_concurrent);
 196                 return pid;
 197         }
 198
 199         /* Block everything but SIGKILL/SIGSTOP */
 200         spin_lock_irq(&current->sigmask_lock);
 201         tmpsig = current->blocked;
 202         siginitsetinv(&current->blocked, sigmask(SIGKILL) | sigmask(SIGSTOP));
 203         recalc_sigpending(current);
 204         spin_unlock_irq(&current->sigmask_lock);
 205
 206         waitpid_result = waitpid(pid, NULL, __WCLONE);
 207         atomic_dec(&kmod_concurrent);
 208
 209         /* Allow signals again.. */
 210         spin_lock_irq(&current->sigmask_lock);
 211         current->blocked = tmpsig;
 212         recalc_sigpending(current);
 213         spin_unlock_irq(&current->sigmask_lock);
 214
 215         if (waitpid_result != pid) {
 216                 printk(KERN_ERR "request_module[%s]: waitpid(%d,...) failed, errno %d\n",
 217                        module_name, pid, -waitpid_result);
 218         }
 219         return 0;
 220 }