1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/mount.h>
3 #include <linux/pseudo_fs.h>
4 #include <linux/file.h>
5 #include <linux/fs.h>
6 #include <linux/proc_fs.h>
7 #include <linux/proc_ns.h>
8 #include <linux/magic.h>
9 #include <linux/ktime.h>
10 #include <linux/seq_file.h>
11 #include <linux/user_namespace.h>
12 #include <linux/nsfs.h>
13 #include <linux/uaccess.h>
14
15 #include "internal.h"
16
17 static struct vfsmount *nsfs_mnt;
18
19 static long ns_ioctl(struct file *filp, unsigned int ioctl,
20 unsigned long arg);
21 static const struct file_operations ns_file_operations = {
22 .llseek = no_llseek,
23 .unlocked_ioctl = ns_ioctl,
24 .compat_ioctl = compat_ptr_ioctl,
25 };
26
ns_dname(struct dentry * dentry,char * buffer,int buflen)27 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
28 {
29 struct inode *inode = d_inode(dentry);
30 const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
31
32 return dynamic_dname(buffer, buflen, "%s:[%lu]",
33 ns_ops->name, inode->i_ino);
34 }
35
ns_prune_dentry(struct dentry * dentry)36 static void ns_prune_dentry(struct dentry *dentry)
37 {
38 struct inode *inode = d_inode(dentry);
39 if (inode) {
40 struct ns_common *ns = inode->i_private;
41 atomic_long_set(&ns->stashed, 0);
42 }
43 }
44
45 const struct dentry_operations ns_dentry_operations =
46 {
47 .d_prune = ns_prune_dentry,
48 .d_delete = always_delete_dentry,
49 .d_dname = ns_dname,
50 };
51
nsfs_evict(struct inode * inode)52 static void nsfs_evict(struct inode *inode)
53 {
54 struct ns_common *ns = inode->i_private;
55 clear_inode(inode);
56 ns->ops->put(ns);
57 }
58
__ns_get_path(struct path * path,struct ns_common * ns)59 static int __ns_get_path(struct path *path, struct ns_common *ns)
60 {
61 struct vfsmount *mnt = nsfs_mnt;
62 struct dentry *dentry;
63 struct inode *inode;
64 unsigned long d;
65
66 rcu_read_lock();
67 d = atomic_long_read(&ns->stashed);
68 if (!d)
69 goto slow;
70 dentry = (struct dentry *)d;
71 if (!lockref_get_not_dead(&dentry->d_lockref))
72 goto slow;
73 rcu_read_unlock();
74 ns->ops->put(ns);
75 got_it:
76 path->mnt = mntget(mnt);
77 path->dentry = dentry;
78 return 0;
79 slow:
80 rcu_read_unlock();
81 inode = new_inode_pseudo(mnt->mnt_sb);
82 if (!inode) {
83 ns->ops->put(ns);
84 return -ENOMEM;
85 }
86 inode->i_ino = ns->inum;
87 inode->i_mtime = inode->i_atime = inode_set_ctime_current(inode);
88 inode->i_flags |= S_IMMUTABLE;
89 inode->i_mode = S_IFREG | S_IRUGO;
90 inode->i_fop = &ns_file_operations;
91 inode->i_private = ns;
92
93 dentry = d_alloc_anon(mnt->mnt_sb);
94 if (!dentry) {
95 iput(inode);
96 return -ENOMEM;
97 }
98 d_instantiate(dentry, inode);
99 dentry->d_fsdata = (void *)ns->ops;
100 d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
101 if (d) {
102 d_delete(dentry); /* make sure ->d_prune() does nothing */
103 dput(dentry);
104 cpu_relax();
105 return -EAGAIN;
106 }
107 goto got_it;
108 }
109
ns_get_path_cb(struct path * path,ns_get_path_helper_t * ns_get_cb,void * private_data)110 int ns_get_path_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
111 void *private_data)
112 {
113 int ret;
114
115 do {
116 struct ns_common *ns = ns_get_cb(private_data);
117 if (!ns)
118 return -ENOENT;
119 ret = __ns_get_path(path, ns);
120 } while (ret == -EAGAIN);
121
122 return ret;
123 }
124
125 struct ns_get_path_task_args {
126 const struct proc_ns_operations *ns_ops;
127 struct task_struct *task;
128 };
129
ns_get_path_task(void * private_data)130 static struct ns_common *ns_get_path_task(void *private_data)
131 {
132 struct ns_get_path_task_args *args = private_data;
133
134 return args->ns_ops->get(args->task);
135 }
136
ns_get_path(struct path * path,struct task_struct * task,const struct proc_ns_operations * ns_ops)137 int ns_get_path(struct path *path, struct task_struct *task,
138 const struct proc_ns_operations *ns_ops)
139 {
140 struct ns_get_path_task_args args = {
141 .ns_ops = ns_ops,
142 .task = task,
143 };
144
145 return ns_get_path_cb(path, ns_get_path_task, &args);
146 }
147
open_related_ns(struct ns_common * ns,struct ns_common * (* get_ns)(struct ns_common * ns))148 int open_related_ns(struct ns_common *ns,
149 struct ns_common *(*get_ns)(struct ns_common *ns))
150 {
151 struct path path = {};
152 struct file *f;
153 int err;
154 int fd;
155
156 fd = get_unused_fd_flags(O_CLOEXEC);
157 if (fd < 0)
158 return fd;
159
160 do {
161 struct ns_common *relative;
162
163 relative = get_ns(ns);
164 if (IS_ERR(relative)) {
165 put_unused_fd(fd);
166 return PTR_ERR(relative);
167 }
168
169 err = __ns_get_path(&path, relative);
170 } while (err == -EAGAIN);
171
172 if (err) {
173 put_unused_fd(fd);
174 return err;
175 }
176
177 f = dentry_open(&path, O_RDONLY, current_cred());
178 path_put(&path);
179 if (IS_ERR(f)) {
180 put_unused_fd(fd);
181 fd = PTR_ERR(f);
182 } else
183 fd_install(fd, f);
184
185 return fd;
186 }
187 EXPORT_SYMBOL_GPL(open_related_ns);
188
ns_ioctl(struct file * filp,unsigned int ioctl,unsigned long arg)189 static long ns_ioctl(struct file *filp, unsigned int ioctl,
190 unsigned long arg)
191 {
192 struct user_namespace *user_ns;
193 struct ns_common *ns = get_proc_ns(file_inode(filp));
194 uid_t __user *argp;
195 uid_t uid;
196
197 switch (ioctl) {
198 case NS_GET_USERNS:
199 return open_related_ns(ns, ns_get_owner);
200 case NS_GET_PARENT:
201 if (!ns->ops->get_parent)
202 return -EINVAL;
203 return open_related_ns(ns, ns->ops->get_parent);
204 case NS_GET_NSTYPE:
205 return ns->ops->type;
206 case NS_GET_OWNER_UID:
207 if (ns->ops->type != CLONE_NEWUSER)
208 return -EINVAL;
209 user_ns = container_of(ns, struct user_namespace, ns);
210 argp = (uid_t __user *) arg;
211 uid = from_kuid_munged(current_user_ns(), user_ns->owner);
212 return put_user(uid, argp);
213 default:
214 return -ENOTTY;
215 }
216 }
217
ns_get_name(char * buf,size_t size,struct task_struct * task,const struct proc_ns_operations * ns_ops)218 int ns_get_name(char *buf, size_t size, struct task_struct *task,
219 const struct proc_ns_operations *ns_ops)
220 {
221 struct ns_common *ns;
222 int res = -ENOENT;
223 const char *name;
224 ns = ns_ops->get(task);
225 if (ns) {
226 name = ns_ops->real_ns_name ? : ns_ops->name;
227 res = snprintf(buf, size, "%s:[%u]", name, ns->inum);
228 ns_ops->put(ns);
229 }
230 return res;
231 }
232
proc_ns_file(const struct file * file)233 bool proc_ns_file(const struct file *file)
234 {
235 return file->f_op == &ns_file_operations;
236 }
237
238 /**
239 * ns_match() - Returns true if current namespace matches dev/ino provided.
240 * @ns: current namespace
241 * @dev: dev_t from nsfs that will be matched against current nsfs
242 * @ino: ino_t from nsfs that will be matched against current nsfs
243 *
244 * Return: true if dev and ino matches the current nsfs.
245 */
ns_match(const struct ns_common * ns,dev_t dev,ino_t ino)246 bool ns_match(const struct ns_common *ns, dev_t dev, ino_t ino)
247 {
248 return (ns->inum == ino) && (nsfs_mnt->mnt_sb->s_dev == dev);
249 }
250
251
nsfs_show_path(struct seq_file * seq,struct dentry * dentry)252 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
253 {
254 struct inode *inode = d_inode(dentry);
255 const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
256
257 seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
258 return 0;
259 }
260
261 static const struct super_operations nsfs_ops = {
262 .statfs = simple_statfs,
263 .evict_inode = nsfs_evict,
264 .show_path = nsfs_show_path,
265 };
266
nsfs_init_fs_context(struct fs_context * fc)267 static int nsfs_init_fs_context(struct fs_context *fc)
268 {
269 struct pseudo_fs_context *ctx = init_pseudo(fc, NSFS_MAGIC);
270 if (!ctx)
271 return -ENOMEM;
272 ctx->ops = &nsfs_ops;
273 ctx->dops = &ns_dentry_operations;
274 return 0;
275 }
276
277 static struct file_system_type nsfs = {
278 .name = "nsfs",
279 .init_fs_context = nsfs_init_fs_context,
280 .kill_sb = kill_anon_super,
281 };
282
nsfs_init(void)283 void __init nsfs_init(void)
284 {
285 nsfs_mnt = kern_mount(&nsfs);
286 if (IS_ERR(nsfs_mnt))
287 panic("can't set nsfs up\n");
288 nsfs_mnt->mnt_sb->s_flags &= ~SB_NOUSER;
289 }
290