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