projects/linux·blob v4.3 · refs

166 lines · 3.3 KiB

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 */
13void set_fs_root(struct fs_struct *fs, const 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 */
32void set_fs_pwd(struct fs_struct *fs, const 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
48static 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
56void chroot_fs_refs(const struct path *old_root, const 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
86void 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
93void 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
110struct 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
131int 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}
152EXPORT_SYMBOL_GPL(unshare_fs_struct);
153
154int current_umask(void)
155{
156 return current->fs->umask;
157}
158EXPORT_SYMBOL(current_umask);
159
160/* to be mentioned only in INIT_TASK */
161struct fs_struct init_fs = {
162 .users = 1,
163 .lock = __SPIN_LOCK_UNLOCKED(init_fs.lock),
164 .seq = SEQCNT_ZERO(init_fs.seq),
165 .umask = 0022,
166};