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 */
15void 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(&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(&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 */
34void 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(&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(&fs->lock);
45
46	if (old_pwd.dentry)
47		path_put(&old_pwd);
48}
49
50static 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
58void 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(&fs->lock);
71			write_seqcount_begin(&fs->seq);
72			hits += replace_path(&fs->root, old_root, new_root);
73			hits += replace_path(&fs->pwd, old_root, new_root);
74			write_seqcount_end(&fs->seq);
75			while (hits--) {
76				count++;
77				path_get(new_root);
78			}
79			spin_unlock(&fs->lock);
80		}
81		task_unlock(p);
82	}
83	read_unlock(&tasklist_lock);
84	while (count--)
85		path_put(old_root);
86}
87
88void free_fs_struct(struct fs_struct *fs)
89{
90	path_put(&fs->root);
91	path_put(&fs->pwd);
92	kmem_cache_free(fs_cachep, fs);
93}
94
95void exit_fs(struct task_struct *tsk)
96{
97	struct fs_struct *fs = tsk->fs;
98
99	if (fs) {
100		int kill;
101		task_lock(tsk);
102		spin_lock(&fs->lock);
103		tsk->fs = NULL;
104		kill = !--fs->users;
105		spin_unlock(&fs->lock);
106		task_unlock(tsk);
107		if (kill)
108			free_fs_struct(fs);
109	}
110}
111
112struct fs_struct *copy_fs_struct(struct fs_struct *old)
113{
114	struct fs_struct *fs = kmem_cache_alloc(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(&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(&old->lock);
129	}
130	return fs;
131}
132
133int unshare_fs_struct(void)
134{
135	struct fs_struct *fs = current->fs;
136	struct fs_struct *new_fs = copy_fs_struct(fs);
137	int kill;
138
139	if (!new_fs)
140		return -ENOMEM;
141
142	task_lock(current);
143	spin_lock(&fs->lock);
144	kill = !--fs->users;
145	current->fs = new_fs;
146	spin_unlock(&fs->lock);
147	task_unlock(current);
148
149	if (kill)
150		free_fs_struct(fs);
151
152	return 0;
153}
154EXPORT_SYMBOL_GPL(unshare_fs_struct);
155
156int current_umask(void)
157{
158	return current->fs->umask;
159}
160EXPORT_SYMBOL(current_umask);
161
162/* to be mentioned only in INIT_TASK */
163struct 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