fs/fs_struct.c

   1 #include <linux/module.h>
   2 #include <linux/sched.h>
   3 #include <linux/fs.h>
   4 #include <linux/path.h>
   5 #include <linux/slab.h>
   6
   7 /*
   8  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
   9  * It can block.
  10  */
  11 void set_fs_root(struct fs_struct *fs, struct path *path)
  12 {
  13         struct path old_root;
  14
  15         write_lock(&fs->lock);
  16         old_root = fs->root;
  17         fs->root = *path;
  18         path_get(path);
  19         write_unlock(&fs->lock);
  20         if (old_root.dentry)
  21                 path_put(&old_root);
  22 }
  23
  24 /*
  25  * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
  26  * It can block.
  27  */
  28 void set_fs_pwd(struct fs_struct *fs, struct path *path)
  29 {
  30         struct path old_pwd;
  31
  32         write_lock(&fs->lock);
  33         old_pwd = fs->pwd;
  34         fs->pwd = *path;
  35         path_get(path);
  36         write_unlock(&fs->lock);
  37
  38         if (old_pwd.dentry)
  39                 path_put(&old_pwd);
  40 }
  41
  42 void chroot_fs_refs(struct path *old_root, struct path *new_root)
  43 {
  44         struct task_struct *g, *p;
  45         struct fs_struct *fs;
  46         int count = 0;
  47
  48         read_lock(&tasklist_lock);
  49         do_each_thread(g, p) {
  50                 task_lock(p);
  51                 fs = p->fs;
  52                 if (fs) {
  53                         write_lock(&fs->lock);
  54                         if (fs->root.dentry == old_root->dentry
  55                             && fs->root.mnt == old_root->mnt) {
  56                                 path_get(new_root);
  57                                 fs->root = *new_root;
  58                                 count++;
  59                         }
  60                         if (fs->pwd.dentry == old_root->dentry
  61                             && fs->pwd.mnt == old_root->mnt) {
  62                                 path_get(new_root);
  63                                 fs->pwd = *new_root;
  64                                 count++;
  65                         }
  66                         write_unlock(&fs->lock);
  67                 }
  68                 task_unlock(p);
  69         } while_each_thread(g, p);
  70         read_unlock(&tasklist_lock);
  71         while (count--)
  72                 path_put(old_root);
  73 }
  74
  75 void free_fs_struct(struct fs_struct *fs)
  76 {
  77         path_put(&fs->root);
  78         path_put(&fs->pwd);
  79         kmem_cache_free(fs_cachep, fs);
  80 }
  81
  82 void exit_fs(struct task_struct *tsk)
  83 {
  84         struct fs_struct *fs = tsk->fs;
  85
  86         if (fs) {
  87                 int kill;
  88                 task_lock(tsk);
  89                 write_lock(&fs->lock);
  90                 tsk->fs = NULL;
  91                 kill = !--fs->users;
  92                 write_unlock(&fs->lock);
  93                 task_unlock(tsk);
  94                 if (kill)
  95                         free_fs_struct(fs);
  96         }
  97 }
  98
  99 struct fs_struct *copy_fs_struct(struct fs_struct *old)
 100 {
 101         struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
 102         /* We don't need to lock fs - think why ;-) */
 103         if (fs) {
 104                 fs->users = 1;
 105                 fs->in_exec = 0;
 106                 rwlock_init(&fs->lock);
 107                 fs->umask = old->umask;
 108                 read_lock(&old->lock);
 109                 fs->root = old->root;
 110                 path_get(&old->root);
 111                 fs->pwd = old->pwd;
 112                 path_get(&old->pwd);
 113                 read_unlock(&old->lock);
 114         }
 115         return fs;
 116 }
 117
 118 int unshare_fs_struct(void)
 119 {
 120         struct fs_struct *fs = current->fs;
 121         struct fs_struct *new_fs = copy_fs_struct(fs);
 122         int kill;
 123
 124         if (!new_fs)
 125                 return -ENOMEM;
 126
 127         task_lock(current);
 128         write_lock(&fs->lock);
 129         kill = !--fs->users;
 130         current->fs = new_fs;
 131         write_unlock(&fs->lock);
 132         task_unlock(current);
 133
 134         if (kill)
 135                 free_fs_struct(fs);
 136
 137         return 0;
 138 }
 139 EXPORT_SYMBOL_GPL(unshare_fs_struct);
 140
 141 /* to be mentioned only in INIT_TASK */
 142 struct fs_struct init_fs = {
 143         .users          = 1,
 144         .lock           = __RW_LOCK_UNLOCKED(init_fs.lock),
 145         .umask          = 0022,
 146 };
 147
 148 void daemonize_fs_struct(void)
 149 {
 150         struct fs_struct *fs = current->fs;
 151
 152         if (fs) {
 153                 int kill;
 154
 155                 task_lock(current);
 156
 157                 write_lock(&init_fs.lock);
 158                 init_fs.users++;
 159                 write_unlock(&init_fs.lock);
 160
 161                 write_lock(&fs->lock);
 162                 current->fs = &init_fs;
 163                 kill = !--fs->users;
 164                 write_unlock(&fs->lock);
 165
 166                 task_unlock(current);
 167                 if (kill)
 168                         free_fs_struct(fs);
 169         }
 170 }