fs/fs_struct.c

   1 #include <linux/export.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 #include "internal.h"
   8
   9 static inline void path_get_longterm(struct path *path)
  10 {
  11         path_get(path);
  12         mnt_make_longterm(path->mnt);
  13 }
  14
  15 static inline void path_put_longterm(struct path *path)
  16 {
  17         mnt_make_shortterm(path->mnt);
  18         path_put(path);
  19 }
  20
  21 /*
  22  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
  23  * It can block.
  24  */
  25 void set_fs_root(struct fs_struct *fs, struct path *path)
  26 {
  27         struct path old_root;
  28
  29         path_get_longterm(path);
  30         spin_lock(&fs->lock);
  31         write_seqcount_begin(&fs->seq);
  32         old_root = fs->root;
  33         fs->root = *path;
  34         write_seqcount_end(&fs->seq);
  35         spin_unlock(&fs->lock);
  36         if (old_root.dentry)
  37                 path_put_longterm(&old_root);
  38 }
  39
  40 /*
  41  * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
  42  * It can block.
  43  */
  44 void set_fs_pwd(struct fs_struct *fs, struct path *path)
  45 {
  46         struct path old_pwd;
  47
  48         path_get_longterm(path);
  49         spin_lock(&fs->lock);
  50         write_seqcount_begin(&fs->seq);
  51         old_pwd = fs->pwd;
  52         fs->pwd = *path;
  53         write_seqcount_end(&fs->seq);
  54         spin_unlock(&fs->lock);
  55
  56         if (old_pwd.dentry)
  57                 path_put_longterm(&old_pwd);
  58 }
  59
  60 static inline int replace_path(struct path *p, const struct path *old, const struct path *new)
  61 {
  62         if (likely(p->dentry != old->dentry || p->mnt != old->mnt))
  63                 return 0;
  64         *p = *new;
  65         return 1;
  66 }
  67
  68 void chroot_fs_refs(struct path *old_root, struct path *new_root)
  69 {
  70         struct task_struct *g, *p;
  71         struct fs_struct *fs;
  72         int count = 0;
  73
  74         read_lock(&tasklist_lock);
  75         do_each_thread(g, p) {
  76                 task_lock(p);
  77                 fs = p->fs;
  78                 if (fs) {
  79                         int hits = 0;
  80                         spin_lock(&fs->lock);
  81                         write_seqcount_begin(&fs->seq);
  82                         hits += replace_path(&fs->root, old_root, new_root);
  83                         hits += replace_path(&fs->pwd, old_root, new_root);
  84                         write_seqcount_end(&fs->seq);
  85                         while (hits--) {
  86                                 count++;
  87                                 path_get_longterm(new_root);
  88                         }
  89                         spin_unlock(&fs->lock);
  90                 }
  91                 task_unlock(p);
  92         } while_each_thread(g, p);
  93         read_unlock(&tasklist_lock);
  94         while (count--)
  95                 path_put_longterm(old_root);
  96 }
  97
  98 void free_fs_struct(struct fs_struct *fs)
  99 {
 100         path_put_longterm(&fs->root);
 101         path_put_longterm(&fs->pwd);
 102         kmem_cache_free(fs_cachep, fs);
 103 }
 104
 105 void exit_fs(struct task_struct *tsk)
 106 {
 107         struct fs_struct *fs = tsk->fs;
 108
 109         if (fs) {
 110                 int kill;
 111                 task_lock(tsk);
 112                 spin_lock(&fs->lock);
 113                 tsk->fs = NULL;
 114                 kill = !--fs->users;
 115                 spin_unlock(&fs->lock);
 116                 task_unlock(tsk);
 117                 if (kill)
 118                         free_fs_struct(fs);
 119         }
 120 }
 121
 122 struct fs_struct *copy_fs_struct(struct fs_struct *old)
 123 {
 124         struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
 125         /* We don't need to lock fs - think why ;-) */
 126         if (fs) {
 127                 fs->users = 1;
 128                 fs->in_exec = 0;
 129                 spin_lock_init(&fs->lock);
 130                 seqcount_init(&fs->seq);
 131                 fs->umask = old->umask;
 132
 133                 spin_lock(&old->lock);
 134                 fs->root = old->root;
 135                 path_get_longterm(&fs->root);
 136                 fs->pwd = old->pwd;
 137                 path_get_longterm(&fs->pwd);
 138                 spin_unlock(&old->lock);
 139         }
 140         return fs;
 141 }
 142
 143 int unshare_fs_struct(void)
 144 {
 145         struct fs_struct *fs = current->fs;
 146         struct fs_struct *new_fs = copy_fs_struct(fs);
 147         int kill;
 148
 149         if (!new_fs)
 150                 return -ENOMEM;
 151
 152         task_lock(current);
 153         spin_lock(&fs->lock);
 154         kill = !--fs->users;
 155         current->fs = new_fs;
 156         spin_unlock(&fs->lock);
 157         task_unlock(current);
 158
 159         if (kill)
 160                 free_fs_struct(fs);
 161
 162         return 0;
 163 }
 164 EXPORT_SYMBOL_GPL(unshare_fs_struct);
 165
 166 int current_umask(void)
 167 {
 168         return current->fs->umask;
 169 }
 170 EXPORT_SYMBOL(current_umask);
 171
 172 /* to be mentioned only in INIT_TASK */
 173 struct fs_struct init_fs = {
 174         .users          = 1,
 175         .lock           = __SPIN_LOCK_UNLOCKED(init_fs.lock),
 176         .seq            = SEQCNT_ZERO,
 177         .umask          = 0022,
 178 };
 179
 180 void daemonize_fs_struct(void)
 181 {
 182         struct fs_struct *fs = current->fs;
 183
 184         if (fs) {
 185                 int kill;
 186
 187                 task_lock(current);
 188
 189                 spin_lock(&init_fs.lock);
 190                 init_fs.users++;
 191                 spin_unlock(&init_fs.lock);
 192
 193                 spin_lock(&fs->lock);
 194                 current->fs = &init_fs;
 195                 kill = !--fs->users;
 196                 spin_unlock(&fs->lock);
 197
 198                 task_unlock(current);
 199                 if (kill)
 200                         free_fs_struct(fs);
 201         }
 202 }