Root/fs/fs_struct.c

1#include <linux/module.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
8/*
9 * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
10 * It can block.
11 */
12void set_fs_root(struct fs_struct *fs, struct path *path)
13{
14    struct path old_root;
15
16    write_lock(&fs->lock);
17    old_root = fs->root;
18    fs->root = *path;
19    path_get(path);
20    write_unlock(&fs->lock);
21    if (old_root.dentry)
22        path_put(&old_root);
23}
24
25/*
26 * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
27 * It can block.
28 */
29void set_fs_pwd(struct fs_struct *fs, struct path *path)
30{
31    struct path old_pwd;
32
33    write_lock(&fs->lock);
34    old_pwd = fs->pwd;
35    fs->pwd = *path;
36    path_get(path);
37    write_unlock(&fs->lock);
38
39    if (old_pwd.dentry)
40        path_put(&old_pwd);
41}
42
43void chroot_fs_refs(struct path *old_root, struct path *new_root)
44{
45    struct task_struct *g, *p;
46    struct fs_struct *fs;
47    int count = 0;
48
49    read_lock(&tasklist_lock);
50    do_each_thread(g, p) {
51        task_lock(p);
52        fs = p->fs;
53        if (fs) {
54            write_lock(&fs->lock);
55            if (fs->root.dentry == old_root->dentry
56                && fs->root.mnt == old_root->mnt) {
57                path_get(new_root);
58                fs->root = *new_root;
59                count++;
60            }
61            if (fs->pwd.dentry == old_root->dentry
62                && fs->pwd.mnt == old_root->mnt) {
63                path_get(new_root);
64                fs->pwd = *new_root;
65                count++;
66            }
67            write_unlock(&fs->lock);
68        }
69        task_unlock(p);
70    } while_each_thread(g, p);
71    read_unlock(&tasklist_lock);
72    while (count--)
73        path_put(old_root);
74}
75
76void free_fs_struct(struct fs_struct *fs)
77{
78    path_put(&fs->root);
79    path_put(&fs->pwd);
80    kmem_cache_free(fs_cachep, fs);
81}
82
83void exit_fs(struct task_struct *tsk)
84{
85    struct fs_struct *fs = tsk->fs;
86
87    if (fs) {
88        int kill;
89        task_lock(tsk);
90        write_lock(&fs->lock);
91        tsk->fs = NULL;
92        kill = !--fs->users;
93        write_unlock(&fs->lock);
94        task_unlock(tsk);
95        if (kill)
96            free_fs_struct(fs);
97    }
98}
99
100struct fs_struct *copy_fs_struct(struct fs_struct *old)
101{
102    struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
103    /* We don't need to lock fs - think why ;-) */
104    if (fs) {
105        fs->users = 1;
106        fs->in_exec = 0;
107        rwlock_init(&fs->lock);
108        fs->umask = old->umask;
109        read_lock(&old->lock);
110        fs->root = old->root;
111        path_get(&old->root);
112        fs->pwd = old->pwd;
113        path_get(&old->pwd);
114        read_unlock(&old->lock);
115    }
116    return fs;
117}
118
119int unshare_fs_struct(void)
120{
121    struct fs_struct *fs = current->fs;
122    struct fs_struct *new_fs = copy_fs_struct(fs);
123    int kill;
124
125    if (!new_fs)
126        return -ENOMEM;
127
128    task_lock(current);
129    write_lock(&fs->lock);
130    kill = !--fs->users;
131    current->fs = new_fs;
132    write_unlock(&fs->lock);
133    task_unlock(current);
134
135    if (kill)
136        free_fs_struct(fs);
137
138    return 0;
139}
140EXPORT_SYMBOL_GPL(unshare_fs_struct);
141
142int current_umask(void)
143{
144    return current->fs->umask;
145}
146EXPORT_SYMBOL(current_umask);
147
148/* to be mentioned only in INIT_TASK */
149struct fs_struct init_fs = {
150    .users = 1,
151    .lock = __RW_LOCK_UNLOCKED(init_fs.lock),
152    .umask = 0022,
153};
154
155void daemonize_fs_struct(void)
156{
157    struct fs_struct *fs = current->fs;
158
159    if (fs) {
160        int kill;
161
162        task_lock(current);
163
164        write_lock(&init_fs.lock);
165        init_fs.users++;
166        write_unlock(&init_fs.lock);
167
168        write_lock(&fs->lock);
169        current->fs = &init_fs;
170        kill = !--fs->users;
171        write_unlock(&fs->lock);
172
173        task_unlock(current);
174        if (kill)
175            free_fs_struct(fs);
176    }
177}
178

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