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/config.h>
  19 #include <linux/sched.h>
  20 #include <linux/unistd.h>
  21 #include <linux/smp_lock.h>
  22
  23 #include <asm/uaccess.h>
  24
  25 /*
  26         modprobe_path is set via /proc/sys.
  27 */
  28 char modprobe_path[256] = "/sbin/modprobe";
  29
  30 extern int max_threads;
  31
  32 static inline void
  33 use_init_fs_context(void)
  34 {
  35         struct fs_struct *our_fs, *init_fs;
  36         struct dentry *root, *pwd;
  37         struct vfsmount *rootmnt, *pwdmnt;
  38
  39         /*
  40          * Make modprobe's fs context be a copy of init's.
  41          *
  42          * We cannot use the user's fs context, because it
  43          * may have a different root than init.
  44          * Since init was created with CLONE_FS, we can grab
  45          * its fs context from "init_task".
  46          *
  47          * The fs context has to be a copy. If it is shared
  48          * with init, then any chdir() call in modprobe will
  49          * also affect init and the other threads sharing
  50          * init_task's fs context.
  51          *
  52          * We created the exec_modprobe thread without CLONE_FS,
  53          * so we can update the fields in our fs context freely.
  54          */
  55
  56         init_fs = init_task.fs;
  57         read_lock(&init_fs->lock);
  58         rootmnt = mntget(init_fs->rootmnt);
  59         root = dget(init_fs->root);
  60         pwdmnt = mntget(init_fs->pwdmnt);
  61         pwd = dget(init_fs->pwd);
  62         read_unlock(&init_fs->lock);
  63
  64         /* FIXME - unsafe ->fs access */
  65         our_fs = current->fs;
  66         our_fs->umask = init_fs->umask;
  67         set_fs_root(our_fs, rootmnt, root);
  68         set_fs_pwd(our_fs, pwdmnt, pwd);
  69         write_lock(&our_fs->lock);
  70         if (our_fs->altroot) {
  71                 struct vfsmount *mnt = our_fs->altrootmnt;
  72                 struct dentry *dentry = our_fs->altroot;
  73                 our_fs->altrootmnt = NULL;
  74                 our_fs->altroot = NULL;
  75                 write_unlock(&our_fs->lock);
  76                 dput(dentry);
  77                 mntput(mnt);
  78         } else
  79                 write_unlock(&our_fs->lock);
  80         dput(root);
  81         mntput(rootmnt);
  82         dput(pwd);
  83         mntput(pwdmnt);
  84 }
  85
  86 int exec_usermodehelper(char *program_path, char *argv[], char *envp[])
  87 {
  88         int i;
  89
  90         current->session = 1;
  91         current->pgrp = 1;
  92
  93         use_init_fs_context();
  94
  95         /* Prevent parent user process from sending signals to child.
  96            Otherwise, if the modprobe program does not exist, it might
  97            be possible to get a user defined signal handler to execute
  98            as the super user right after the execve fails if you time
  99            the signal just right.
 100         */
 101         spin_lock_irq(&current->sigmask_lock);
 102         flush_signals(current);
 103         flush_signal_handlers(current);
 104         spin_unlock_irq(&current->sigmask_lock);
 105
 106         for (i = 0; i < current->files->max_fds; i++ ) {
 107                 if (current->files->fd[i]) close(i);
 108         }
 109
 110         /* Drop the "current user" thing */
 111         {
 112                 struct user_struct *user = current->user;
 113                 current->user = INIT_USER;
 114                 atomic_inc(&INIT_USER->__count);
 115                 atomic_inc(&INIT_USER->processes);
 116                 atomic_dec(&user->processes);
 117                 free_uid(user);
 118         }
 119
 120         /* Give kmod all effective privileges.. */
 121         current->uid = current->euid = current->fsuid = 0;
 122         cap_set_full(current->cap_effective);
 123
 124         /* Allow execve args to be in kernel space. */
 125         set_fs(KERNEL_DS);
 126
 127         /* Go, go, go... */
 128         if (execve(program_path, argv, envp) < 0)
 129                 return -errno;
 130         return 0;
 131 }
 132
 133 static int exec_modprobe(void * module_name)
 134 {
 135         static char * envp[] = { "HOME=/", "TERM=linux", "PATH=/sbin:/usr/sbin:/bin:/usr/bin", NULL };
 136         char *argv[] = { modprobe_path, "-s", "-k", (char*)module_name, NULL };
 137         int ret;
 138
 139         ret = exec_usermodehelper(modprobe_path, argv, envp);
 140         if (ret) {
 141                 printk(KERN_ERR
 142                        "kmod: failed to exec %s -s -k %s, errno = %d\n",
 143                        modprobe_path, (char*) module_name, errno);
 144         }
 145         return ret;
 146 }
 147
 148 /**
 149  *      request_module - try to load a kernel module
 150  *      @module_name: Name of module
 151  *
 152  *      Load a module using the user mode module loader. The function returns
 153  *      zero on success or a negative errno code on failure. Note that a
 154  *      successful module load does not mean the module did not then unload
 155  *      and exit on an error of its own. Callers must check that the service
 156  *      they requested is now available not blindly invoke it.
 157  *
 158  *      If module auto-loading support is disabled then this function
 159  *      becomes a no-operation.
 160  */
 161
 162 int request_module(const char * module_name)
 163 {
 164         int pid;
 165         int waitpid_result;
 166         sigset_t tmpsig;
 167         int i;
 168         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
 169 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
 170         static int kmod_loop_msg;
 171
 172         /* Don't allow request_module() before the root fs is mounted!  */
 173         if ( ! current->fs->root ) {
 174                 printk(KERN_ERR "request_module[%s]: Root fs not mounted\n",
 175                         module_name);
 176                 return -EPERM;
 177         }
 178
 179         /* If modprobe needs a service that is in a module, we get a recursive
 180          * loop.  Limit the number of running kmod threads to max_threads/2 or
 181          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
 182          * would be to run the parents of this process, counting how many times
 183          * kmod was invoked.  That would mean accessing the internals of the
 184          * process tables to get the command line, proc_pid_cmdline is static
 185          * and it is not worth changing the proc code just to handle this case.
 186          * KAO.
 187          */
 188         i = max_threads/2;
 189         if (i > MAX_KMOD_CONCURRENT)
 190                 i = MAX_KMOD_CONCURRENT;
 191         atomic_inc(&kmod_concurrent);
 192         if (atomic_read(&kmod_concurrent) > i) {
 193                 if (kmod_loop_msg++ < 5)
 194                         printk(KERN_ERR
 195                                "kmod: runaway modprobe loop assumed and stopped\n");
 196                 atomic_dec(&kmod_concurrent);
 197                 return -ENOMEM;
 198         }
 199
 200         pid = kernel_thread(exec_modprobe, (void*) module_name, 0);
 201         if (pid < 0) {
 202                 printk(KERN_ERR "request_module[%s]: fork failed, errno %d\n", module_name, -pid);
 203                 atomic_dec(&kmod_concurrent);
 204                 return pid;
 205         }
 206
 207         /* Block everything but SIGKILL/SIGSTOP */
 208         spin_lock_irq(&current->sigmask_lock);
 209         tmpsig = current->blocked;
 210         siginitsetinv(&current->blocked, sigmask(SIGKILL) | sigmask(SIGSTOP));
 211         recalc_sigpending(current);
 212         spin_unlock_irq(&current->sigmask_lock);
 213
 214         waitpid_result = waitpid(pid, NULL, __WCLONE);
 215         atomic_dec(&kmod_concurrent);
 216
 217         /* Allow signals again.. */
 218         spin_lock_irq(&current->sigmask_lock);
 219         current->blocked = tmpsig;
 220         recalc_sigpending(current);
 221         spin_unlock_irq(&current->sigmask_lock);
 222
 223         if (waitpid_result != pid) {
 224                 printk(KERN_ERR "request_module[%s]: waitpid(%d,...) failed, errno %d\n",
 225                        module_name, pid, -waitpid_result);
 226         }
 227         return 0;
 228 }
 229
 230
 231 #ifdef CONFIG_HOTPLUG
 232 /*
 233         hotplug path is set via /proc/sys
 234         invoked by hotplug-aware bus drivers,
 235         with exec_usermodehelper and some thread-spawner
 236
 237         argv [0] = hotplug_path;
 238         argv [1] = "usb", "scsi", "pci", "network", etc;
 239         ... plus optional type-specific parameters
 240         argv [n] = 0;
 241
 242         envp [*] = HOME, PATH; optional type-specific parameters
 243
 244         a hotplug bus should invoke this for device add/remove
 245         events.  the command is expected to load drivers when
 246         necessary, and may perform additional system setup.
 247 */
 248 char hotplug_path[256] = "/sbin/hotplug";
 249
 250 #endif
 251