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 #include <linux/fs_struct.h>
   7
   8 /*
   9  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
  10  * It can block.
  11  */
  12 void set_fs_root(struct fs_struct *fs, struct path *path)
  13 {
  14         struct path old_root;
  15
  16         spin_lock(&fs->lock);
  17         write_seqcount_begin(&fs->seq);
  18         old_root = fs->root;
  19         fs->root = *path;
  20         path_get_long(path);
  21         write_seqcount_end(&fs->seq);
  22         spin_unlock(&fs->lock);
  23         if (old_root.dentry)
  24                 path_put_long(&old_root);
  25 }
  26
  27 /*
  28  * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
  29  * It can block.
  30  */
  31 void set_fs_pwd(struct fs_struct *fs, struct path *path)
  32 {
  33         struct path old_pwd;
  34
  35         spin_lock(&fs->lock);
  36         write_seqcount_begin(&fs->seq);
  37         old_pwd = fs->pwd;
  38         fs->pwd = *path;
  39         path_get_long(path);
  40         write_seqcount_end(&fs->seq);
  41         spin_unlock(&fs->lock);
  42
  43         if (old_pwd.dentry)
  44                 path_put_long(&old_pwd);
  45 }
  46
  47 void chroot_fs_refs(struct path *old_root, struct path *new_root)
  48 {
  49         struct task_struct *g, *p;
  50         struct fs_struct *fs;
  51         int count = 0;
  52
  53         read_lock(&tasklist_lock);
  54         do_each_thread(g, p) {
  55                 task_lock(p);
  56                 fs = p->fs;
  57                 if (fs) {
  58                         spin_lock(&fs->lock);
  59                         write_seqcount_begin(&fs->seq);
  60                         if (fs->root.dentry == old_root->dentry
  61                             && fs->root.mnt == old_root->mnt) {
  62                                 path_get_long(new_root);
  63                                 fs->root = *new_root;
  64                                 count++;
  65                         }
  66                         if (fs->pwd.dentry == old_root->dentry
  67                             && fs->pwd.mnt == old_root->mnt) {
  68                                 path_get_long(new_root);
  69                                 fs->pwd = *new_root;
  70                                 count++;
  71                         }
  72                         write_seqcount_end(&fs->seq);
  73                         spin_unlock(&fs->lock);
  74                 }
  75                 task_unlock(p);
  76         } while_each_thread(g, p);
  77         read_unlock(&tasklist_lock);
  78         while (count--)
  79                 path_put_long(old_root);
  80 }
  81
  82 void free_fs_struct(struct fs_struct *fs)
  83 {
  84         path_put_long(&fs->root);
  85         path_put_long(&fs->pwd);
  86         kmem_cache_free(fs_cachep, fs);
  87 }
  88
  89 void exit_fs(struct task_struct *tsk)
  90 {
  91         struct fs_struct *fs = tsk->fs;
  92
  93         if (fs) {
  94                 int kill;
  95                 task_lock(tsk);
  96                 spin_lock(&fs->lock);
  97                 write_seqcount_begin(&fs->seq);
  98                 tsk->fs = NULL;
  99                 kill = !--fs->users;
 100                 write_seqcount_end(&fs->seq);
 101                 spin_unlock(&fs->lock);
 102                 task_unlock(tsk);
 103                 if (kill)
 104                         free_fs_struct(fs);
 105         }
 106 }
 107
 108 struct fs_struct *copy_fs_struct(struct fs_struct *old)
 109 {
 110         struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
 111         /* We don't need to lock fs - think why ;-) */
 112         if (fs) {
 113                 fs->users = 1;
 114                 fs->in_exec = 0;
 115                 spin_lock_init(&fs->lock);
 116                 seqcount_init(&fs->seq);
 117                 fs->umask = old->umask;
 118
 119                 spin_lock(&old->lock);
 120                 fs->root = old->root;
 121                 path_get_long(&fs->root);
 122                 fs->pwd = old->pwd;
 123                 path_get_long(&fs->pwd);
 124                 spin_unlock(&old->lock);
 125         }
 126         return fs;
 127 }
 128
 129 int unshare_fs_struct(void)
 130 {
 131         struct fs_struct *fs = current->fs;
 132         struct fs_struct *new_fs = copy_fs_struct(fs);
 133         int kill;
 134
 135         if (!new_fs)
 136                 return -ENOMEM;
 137
 138         task_lock(current);
 139         spin_lock(&fs->lock);
 140         kill = !--fs->users;
 141         current->fs = new_fs;
 142         spin_unlock(&fs->lock);
 143         task_unlock(current);
 144
 145         if (kill)
 146                 free_fs_struct(fs);
 147
 148         return 0;
 149 }
 150 EXPORT_SYMBOL_GPL(unshare_fs_struct);
 151
 152 int current_umask(void)
 153 {
 154         return current->fs->umask;
 155 }
 156 EXPORT_SYMBOL(current_umask);
 157
 158 /* to be mentioned only in INIT_TASK */
 159 struct fs_struct init_fs = {
 160         .users          = 1,
 161         .lock           = __SPIN_LOCK_UNLOCKED(init_fs.lock),
 162         .seq            = SEQCNT_ZERO,
 163         .umask          = 0022,
 164 };
 165
 166 void daemonize_fs_struct(void)
 167 {
 168         struct fs_struct *fs = current->fs;
 169
 170         if (fs) {
 171                 int kill;
 172
 173                 task_lock(current);
 174
 175                 spin_lock(&init_fs.lock);
 176                 init_fs.users++;
 177                 spin_unlock(&init_fs.lock);
 178
 179                 spin_lock(&fs->lock);
 180                 current->fs = &init_fs;
 181                 kill = !--fs->users;
 182                 spin_unlock(&fs->lock);
 183
 184                 task_unlock(current);
 185                 if (kill)
 186                         free_fs_struct(fs);
 187         }
 188 }