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 } 191