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