xref: /openbmc/linux/fs/fs_struct.c (revision 5ffd2c37)
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  */
set_fs_root(struct fs_struct * fs,const struct path * path)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(&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  */
set_fs_pwd(struct fs_struct * fs,const struct path * path)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(&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 
replace_path(struct path * p,const struct path * old,const struct path * new)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 
chroot_fs_refs(const struct path * old_root,const struct path * new_root)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(&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 
free_fs_struct(struct fs_struct * fs)88 void 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 
exit_fs(struct task_struct * tsk)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(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 
copy_fs_struct(struct fs_struct * old)112 struct 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 
unshare_fs_struct(void)133 int 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 }
154 EXPORT_SYMBOL_GPL(unshare_fs_struct);
155 
current_umask(void)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