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 #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         spin_lock(&fs->lock);
  30         write_seqcount_begin(&fs->seq);
  31         old_root = fs->root;
  32         fs->root = *path;
  33         path_get_longterm(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         spin_lock(&fs->lock);
  49         write_seqcount_begin(&fs->seq);
  50         old_pwd = fs->pwd;
  51         fs->pwd = *path;
  52         path_get_longterm(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 void chroot_fs_refs(struct path *old_root, struct path *new_root)
  61 {
  62         struct task_struct *g, *p;
  63         struct fs_struct *fs;
  64         int count = 0;
  65
  66         read_lock(&tasklist_lock);
  67         do_each_thread(g, p) {
  68                 task_lock(p);
  69                 fs = p->fs;
  70                 if (fs) {
  71                         spin_lock(&fs->lock);
  72                         write_seqcount_begin(&fs->seq);
  73                         if (fs->root.dentry == old_root->dentry
  74                             && fs->root.mnt == old_root->mnt) {
  75                                 path_get_longterm(new_root);
  76                                 fs->root = *new_root;
  77                                 count++;
  78                         }
  79                         if (fs->pwd.dentry == old_root->dentry
  80                             && fs->pwd.mnt == old_root->mnt) {
  81                                 path_get_longterm(new_root);
  82                                 fs->pwd = *new_root;
  83                                 count++;
  84                         }
  85                         write_seqcount_end(&fs->seq);
  86                         spin_unlock(&fs->lock);
  87                 }
  88                 task_unlock(p);
  89         } while_each_thread(g, p);
  90         read_unlock(&tasklist_lock);
  91         while (count--)
  92                 path_put_longterm(old_root);
  93 }
  94
  95 void free_fs_struct(struct fs_struct *fs)
  96 {
  97         path_put_longterm(&fs->root);
  98         path_put_longterm(&fs->pwd);
  99         kmem_cache_free(fs_cachep, fs);
 100 }
 101
 102 void exit_fs(struct task_struct *tsk)
 103 {
 104         struct fs_struct *fs = tsk->fs;
 105
 106         if (fs) {
 107                 int kill;
 108                 task_lock(tsk);
 109                 spin_lock(&fs->lock);
 110                 write_seqcount_begin(&fs->seq);
 111                 tsk->fs = NULL;
 112                 kill = !--fs->users;
 113                 write_seqcount_end(&fs->seq);
 114                 spin_unlock(&fs->lock);
 115                 task_unlock(tsk);
 116                 if (kill)
 117                         free_fs_struct(fs);
 118         }
 119 }
 120
 121 struct fs_struct *copy_fs_struct(struct fs_struct *old)
 122 {
 123         struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
 124         /* We don't need to lock fs - think why ;-) */
 125         if (fs) {
 126                 fs->users = 1;
 127                 fs->in_exec = 0;
 128                 spin_lock_init(&fs->lock);
 129                 seqcount_init(&fs->seq);
 130                 fs->umask = old->umask;
 131
 132                 spin_lock(&old->lock);
 133                 fs->root = old->root;
 134                 path_get_longterm(&fs->root);
 135                 fs->pwd = old->pwd;
 136                 path_get_longterm(&fs->pwd);
 137                 spin_unlock(&old->lock);
 138         }
 139         return fs;
 140 }
 141
 142 int unshare_fs_struct(void)
 143 {
 144         struct fs_struct *fs = current->fs;
 145         struct fs_struct *new_fs = copy_fs_struct(fs);
 146         int kill;
 147
 148         if (!new_fs)
 149                 return -ENOMEM;
 150
 151         task_lock(current);
 152         spin_lock(&fs->lock);
 153         kill = !--fs->users;
 154         current->fs = new_fs;
 155         spin_unlock(&fs->lock);
 156         task_unlock(current);
 157
 158         if (kill)
 159                 free_fs_struct(fs);
 160
 161         return 0;
 162 }
 163 EXPORT_SYMBOL_GPL(unshare_fs_struct);
 164
 165 int current_umask(void)
 166 {
 167         return current->fs->umask;
 168 }
 169 EXPORT_SYMBOL(current_umask);
 170
 171 /* to be mentioned only in INIT_TASK */
 172 struct fs_struct init_fs = {
 173         .users          = 1,
 174         .lock           = __SPIN_LOCK_UNLOCKED(init_fs.lock),
 175         .seq            = SEQCNT_ZERO,
 176         .umask          = 0022,
 177 };
 178
 179 void daemonize_fs_struct(void)
 180 {
 181         struct fs_struct *fs = current->fs;
 182
 183         if (fs) {
 184                 int kill;
 185
 186                 task_lock(current);
 187
 188                 spin_lock(&init_fs.lock);
 189                 init_fs.users++;
 190                 spin_unlock(&init_fs.lock);
 191
 192                 spin_lock(&fs->lock);
 193                 current->fs = &init_fs;
 194                 kill = !--fs->users;
 195                 spin_unlock(&fs->lock);
 196
 197                 task_unlock(current);
 198                 if (kill)
 199                         free_fs_struct(fs);
 200         }
 201 }