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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, 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 | */ | |
32 | void 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 | ||
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(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 | ||
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(init_fs.seq), | |
165 | .umask = 0022, | |
166 | }; |