1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | #include <linux/export.h> |
3 | #include <linux/sched/signal.h> |
4 | #include <linux/sched/task.h> |
5 | #include <linux/fs.h> |
6 | #include <linux/path.h> |
7 | #include <linux/slab.h> |
8 | #include <linux/fs_struct.h> |
9 | #include "internal.h" |
10 | |
11 | /* |
12 | * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values. |
13 | * It can block. |
14 | */ |
15 | void set_fs_root(struct fs_struct *fs, const struct path *path) |
16 | { |
17 | struct path old_root; |
18 | |
19 | path_get(path); |
20 | spin_lock(lock: &fs->lock); |
21 | write_seqcount_begin(&fs->seq); |
22 | old_root = fs->root; |
23 | fs->root = *path; |
24 | write_seqcount_end(&fs->seq); |
25 | spin_unlock(lock: &fs->lock); |
26 | if (old_root.dentry) |
27 | path_put(&old_root); |
28 | } |
29 | |
30 | /* |
31 | * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values. |
32 | * It can block. |
33 | */ |
34 | void set_fs_pwd(struct fs_struct *fs, const struct path *path) |
35 | { |
36 | struct path old_pwd; |
37 | |
38 | path_get(path); |
39 | spin_lock(lock: &fs->lock); |
40 | write_seqcount_begin(&fs->seq); |
41 | old_pwd = fs->pwd; |
42 | fs->pwd = *path; |
43 | write_seqcount_end(&fs->seq); |
44 | spin_unlock(lock: &fs->lock); |
45 | |
46 | if (old_pwd.dentry) |
47 | path_put(&old_pwd); |
48 | } |
49 | |
50 | static inline int replace_path(struct path *p, const struct path *old, const struct path *new) |
51 | { |
52 | if (likely(p->dentry != old->dentry || p->mnt != old->mnt)) |
53 | return 0; |
54 | *p = *new; |
55 | return 1; |
56 | } |
57 | |
58 | void chroot_fs_refs(const struct path *old_root, const struct path *new_root) |
59 | { |
60 | struct task_struct *g, *p; |
61 | struct fs_struct *fs; |
62 | int count = 0; |
63 | |
64 | read_lock(&tasklist_lock); |
65 | for_each_process_thread(g, p) { |
66 | task_lock(p); |
67 | fs = p->fs; |
68 | if (fs) { |
69 | int hits = 0; |
70 | spin_lock(lock: &fs->lock); |
71 | write_seqcount_begin(&fs->seq); |
72 | hits += replace_path(p: &fs->root, old: old_root, new: new_root); |
73 | hits += replace_path(p: &fs->pwd, old: old_root, new: new_root); |
74 | write_seqcount_end(&fs->seq); |
75 | while (hits--) { |
76 | count++; |
77 | path_get(new_root); |
78 | } |
79 | spin_unlock(lock: &fs->lock); |
80 | } |
81 | task_unlock(p); |
82 | } |
83 | read_unlock(&tasklist_lock); |
84 | while (count--) |
85 | path_put(old_root); |
86 | } |
87 | |
88 | void free_fs_struct(struct fs_struct *fs) |
89 | { |
90 | path_put(&fs->root); |
91 | path_put(&fs->pwd); |
92 | kmem_cache_free(s: fs_cachep, objp: fs); |
93 | } |
94 | |
95 | void exit_fs(struct task_struct *tsk) |
96 | { |
97 | struct fs_struct *fs = tsk->fs; |
98 | |
99 | if (fs) { |
100 | int kill; |
101 | task_lock(p: tsk); |
102 | spin_lock(lock: &fs->lock); |
103 | tsk->fs = NULL; |
104 | kill = !--fs->users; |
105 | spin_unlock(lock: &fs->lock); |
106 | task_unlock(p: tsk); |
107 | if (kill) |
108 | free_fs_struct(fs); |
109 | } |
110 | } |
111 | |
112 | struct fs_struct *copy_fs_struct(struct fs_struct *old) |
113 | { |
114 | struct fs_struct *fs = kmem_cache_alloc(cachep: fs_cachep, GFP_KERNEL); |
115 | /* We don't need to lock fs - think why ;-) */ |
116 | if (fs) { |
117 | fs->users = 1; |
118 | fs->in_exec = 0; |
119 | spin_lock_init(&fs->lock); |
120 | seqcount_spinlock_init(&fs->seq, &fs->lock); |
121 | fs->umask = old->umask; |
122 | |
123 | spin_lock(lock: &old->lock); |
124 | fs->root = old->root; |
125 | path_get(&fs->root); |
126 | fs->pwd = old->pwd; |
127 | path_get(&fs->pwd); |
128 | spin_unlock(lock: &old->lock); |
129 | } |
130 | return fs; |
131 | } |
132 | |
133 | int unshare_fs_struct(void) |
134 | { |
135 | struct fs_struct *fs = current->fs; |
136 | struct fs_struct *new_fs = copy_fs_struct(old: fs); |
137 | int kill; |
138 | |
139 | if (!new_fs) |
140 | return -ENOMEM; |
141 | |
142 | task_lock(current); |
143 | spin_lock(lock: &fs->lock); |
144 | kill = !--fs->users; |
145 | current->fs = new_fs; |
146 | spin_unlock(lock: &fs->lock); |
147 | task_unlock(current); |
148 | |
149 | if (kill) |
150 | free_fs_struct(fs); |
151 | |
152 | return 0; |
153 | } |
154 | EXPORT_SYMBOL_GPL(unshare_fs_struct); |
155 | |
156 | int current_umask(void) |
157 | { |
158 | return current->fs->umask; |
159 | } |
160 | EXPORT_SYMBOL(current_umask); |
161 | |
162 | /* to be mentioned only in INIT_TASK */ |
163 | struct fs_struct init_fs = { |
164 | .users = 1, |
165 | .lock = __SPIN_LOCK_UNLOCKED(init_fs.lock), |
166 | .seq = SEQCNT_SPINLOCK_ZERO(init_fs.seq, &init_fs.lock), |
167 | .umask = 0022, |
168 | }; |
169 | |