1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/syscalls.h>
3 #include <linux/slab.h>
4 #include <linux/fs.h>
5 #include <linux/file.h>
6 #include <linux/mount.h>
7 #include <linux/namei.h>
8 #include <linux/exportfs.h>
9 #include <linux/fs_struct.h>
10 #include <linux/fsnotify.h>
11 #include <linux/personality.h>
12 #include <linux/uaccess.h>
13 #include <linux/compat.h>
14 #include <linux/nsfs.h>
15 #include "internal.h"
16 #include "mount.h"
17
do_sys_name_to_handle(const struct path * path,struct file_handle __user * ufh,void __user * mnt_id,bool unique_mntid,int fh_flags)18 static long do_sys_name_to_handle(const struct path *path,
19 struct file_handle __user *ufh,
20 void __user *mnt_id, bool unique_mntid,
21 int fh_flags)
22 {
23 long retval;
24 struct file_handle f_handle;
25 int handle_dwords, handle_bytes;
26 struct file_handle *handle = NULL;
27
28 /*
29 * We need to make sure whether the file system support decoding of
30 * the file handle if decodeable file handle was requested.
31 */
32 if (!exportfs_can_encode_fh(path->dentry->d_sb->s_export_op, fh_flags))
33 return -EOPNOTSUPP;
34
35 /*
36 * A request to encode a connectable handle for a disconnected dentry
37 * is unexpected since AT_EMPTY_PATH is not allowed.
38 */
39 if (fh_flags & EXPORT_FH_CONNECTABLE &&
40 WARN_ON(path->dentry->d_flags & DCACHE_DISCONNECTED))
41 return -EINVAL;
42
43 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
44 return -EFAULT;
45
46 if (f_handle.handle_bytes > MAX_HANDLE_SZ)
47 return -EINVAL;
48
49 handle = kzalloc_flex(*handle, f_handle, f_handle.handle_bytes);
50 if (!handle)
51 return -ENOMEM;
52
53 /* convert handle size to multiple of sizeof(u32) */
54 handle_dwords = f_handle.handle_bytes >> 2;
55
56 /* Encode a possibly decodeable/connectable file handle */
57 retval = exportfs_encode_fh(path->dentry,
58 (struct fid *)handle->f_handle,
59 &handle_dwords, fh_flags);
60 handle->handle_type = retval;
61 /* convert handle size to bytes */
62 handle_bytes = handle_dwords * sizeof(u32);
63 handle->handle_bytes = handle_bytes;
64 if ((handle->handle_bytes > f_handle.handle_bytes) ||
65 (retval == FILEID_INVALID) || (retval < 0)) {
66 /* As per old exportfs_encode_fh documentation
67 * we could return ENOSPC to indicate overflow
68 * But file system returned 255 always. So handle
69 * both the values
70 */
71 if (retval == FILEID_INVALID || retval == -ENOSPC)
72 retval = -EOVERFLOW;
73 /*
74 * set the handle size to zero so we copy only
75 * non variable part of the file_handle
76 */
77 handle_bytes = 0;
78 } else {
79 /*
80 * When asked to encode a connectable file handle, encode this
81 * property in the file handle itself, so that we later know
82 * how to decode it.
83 * For sanity, also encode in the file handle if the encoded
84 * object is a directory and verify this during decode, because
85 * decoding directory file handles is quite different than
86 * decoding connectable non-directory file handles.
87 */
88 if (fh_flags & EXPORT_FH_CONNECTABLE) {
89 handle->handle_type |= FILEID_IS_CONNECTABLE;
90 if (d_is_dir(path->dentry))
91 handle->handle_type |= FILEID_IS_DIR;
92 }
93 retval = 0;
94 }
95 /* copy the mount id */
96 if (unique_mntid) {
97 if (put_user(real_mount(path->mnt)->mnt_id_unique,
98 (u64 __user *) mnt_id))
99 retval = -EFAULT;
100 } else {
101 if (put_user(real_mount(path->mnt)->mnt_id,
102 (int __user *) mnt_id))
103 retval = -EFAULT;
104 }
105 /* copy the handle */
106 if (retval != -EFAULT &&
107 copy_to_user(ufh, handle,
108 struct_size(handle, f_handle, handle_bytes)))
109 retval = -EFAULT;
110 kfree(handle);
111 return retval;
112 }
113
114 /**
115 * sys_name_to_handle_at: convert name to handle
116 * @dfd: directory relative to which name is interpreted if not absolute
117 * @name: name that should be converted to handle.
118 * @handle: resulting file handle
119 * @mnt_id: mount id of the file system containing the file
120 * (u64 if AT_HANDLE_MNT_ID_UNIQUE, otherwise int)
121 * @flag: flag value to indicate whether to follow symlink or not
122 * and whether a decodable file handle is required.
123 *
124 * @handle->handle_size indicate the space available to store the
125 * variable part of the file handle in bytes. If there is not
126 * enough space, the field is updated to return the minimum
127 * value required.
128 */
SYSCALL_DEFINE5(name_to_handle_at,int,dfd,const char __user *,name,struct file_handle __user *,handle,void __user *,mnt_id,int,flag)129 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
130 struct file_handle __user *, handle, void __user *, mnt_id,
131 int, flag)
132 {
133 struct path path;
134 int lookup_flags;
135 int fh_flags = 0;
136 int err;
137
138 if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID |
139 AT_HANDLE_MNT_ID_UNIQUE | AT_HANDLE_CONNECTABLE))
140 return -EINVAL;
141
142 /*
143 * AT_HANDLE_FID means there is no intention to decode file handle
144 * AT_HANDLE_CONNECTABLE means there is an intention to decode a
145 * connected fd (with known path), so these flags are conflicting.
146 * AT_EMPTY_PATH could be used along with a dfd that refers to a
147 * disconnected non-directory, which cannot be used to encode a
148 * connectable file handle, because its parent is unknown.
149 */
150 if (flag & AT_HANDLE_CONNECTABLE &&
151 flag & (AT_HANDLE_FID | AT_EMPTY_PATH))
152 return -EINVAL;
153 else if (flag & AT_HANDLE_FID)
154 fh_flags |= EXPORT_FH_FID;
155 else if (flag & AT_HANDLE_CONNECTABLE)
156 fh_flags |= EXPORT_FH_CONNECTABLE;
157
158 lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
159 CLASS(filename_uflags, filename)(name, flag);
160 err = filename_lookup(dfd, filename, lookup_flags, &path, NULL);
161 if (!err) {
162 err = do_sys_name_to_handle(&path, handle, mnt_id,
163 flag & AT_HANDLE_MNT_ID_UNIQUE,
164 fh_flags);
165 path_put(&path);
166 }
167 return err;
168 }
169
get_path_anchor(int fd,struct path * root)170 static int get_path_anchor(int fd, struct path *root)
171 {
172 if (fd >= 0) {
173 CLASS(fd, f)(fd);
174 if (fd_empty(f))
175 return -EBADF;
176 *root = fd_file(f)->f_path;
177 path_get(root);
178 return 0;
179 }
180
181 if (fd == AT_FDCWD) {
182 get_fs_pwd(current->fs, root);
183 return 0;
184 }
185
186 if (fd == FD_PIDFS_ROOT) {
187 pidfs_get_root(root);
188 return 0;
189 }
190
191 if (fd == FD_NSFS_ROOT) {
192 nsfs_get_root(root);
193 return 0;
194 }
195
196 return -EBADF;
197 }
198
vfs_dentry_acceptable(void * context,struct dentry * dentry)199 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
200 {
201 struct handle_to_path_ctx *ctx = context;
202 struct user_namespace *user_ns = current_user_ns();
203 struct dentry *d, *root = ctx->root.dentry;
204 struct mnt_idmap *idmap = mnt_idmap(ctx->root.mnt);
205 int retval = 0;
206
207 if (!root)
208 return 1;
209
210 /* Old permission model with global CAP_DAC_READ_SEARCH. */
211 if (!ctx->flags)
212 return 1;
213
214 /*
215 * Verify that the decoded dentry itself has a valid id mapping.
216 * In case the decoded dentry is the mountfd root itself, this
217 * verifies that the mountfd inode itself has a valid id mapping.
218 */
219 if (!privileged_wrt_inode_uidgid(user_ns, idmap, d_inode(dentry)))
220 return 0;
221
222 /*
223 * It's racy as we're not taking rename_lock but we're able to ignore
224 * permissions and we just need an approximation whether we were able
225 * to follow a path to the file.
226 *
227 * It's also potentially expensive on some filesystems especially if
228 * there is a deep path.
229 */
230 d = dget(dentry);
231 while (d != root && !IS_ROOT(d)) {
232 struct dentry *parent = dget_parent(d);
233
234 /*
235 * We know that we have the ability to override DAC permissions
236 * as we've verified this earlier via CAP_DAC_READ_SEARCH. But
237 * we also need to make sure that there aren't any unmapped
238 * inodes in the path that would prevent us from reaching the
239 * file.
240 */
241 if (!privileged_wrt_inode_uidgid(user_ns, idmap,
242 d_inode(parent))) {
243 dput(d);
244 dput(parent);
245 return retval;
246 }
247
248 dput(d);
249 d = parent;
250 }
251
252 if (!(ctx->flags & HANDLE_CHECK_SUBTREE) || d == root)
253 retval = 1;
254 /*
255 * exportfs_decode_fh_raw() does not call acceptable() callback with
256 * a disconnected directory dentry, so we should have reached either
257 * mount fd directory or sb root.
258 */
259 if (ctx->fh_flags & EXPORT_FH_DIR_ONLY)
260 WARN_ON_ONCE(d != root && d != root->d_sb->s_root);
261 dput(d);
262 return retval;
263 }
264
do_handle_to_path(struct file_handle * handle,struct path * path,struct handle_to_path_ctx * ctx)265 static int do_handle_to_path(struct file_handle *handle, struct path *path,
266 struct handle_to_path_ctx *ctx)
267 {
268 int handle_dwords;
269 struct vfsmount *mnt = ctx->root.mnt;
270 struct dentry *dentry;
271
272 /* change the handle size to multiple of sizeof(u32) */
273 handle_dwords = handle->handle_bytes >> 2;
274 dentry = exportfs_decode_fh_raw(mnt, (struct fid *)handle->f_handle,
275 handle_dwords, handle->handle_type,
276 ctx->fh_flags, vfs_dentry_acceptable,
277 ctx);
278 if (IS_ERR_OR_NULL(dentry)) {
279 if (dentry == ERR_PTR(-ENOMEM))
280 return -ENOMEM;
281 return -ESTALE;
282 }
283 path->dentry = dentry;
284 path->mnt = mntget(mnt);
285 return 0;
286 }
287
capable_wrt_mount(struct mount * mount)288 static bool capable_wrt_mount(struct mount *mount)
289 {
290 struct mnt_namespace *mnt_ns;
291
292 /*
293 * For ->mnt_ns access.
294 * The following READ_ONCE() is semantically rcu_dereference().
295 */
296 guard(rcu)();
297 mnt_ns = READ_ONCE(mount->mnt_ns);
298 return ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN);
299 }
300
may_decode_fh(struct handle_to_path_ctx * ctx,unsigned int o_flags)301 static inline int may_decode_fh(struct handle_to_path_ctx *ctx,
302 unsigned int o_flags)
303 {
304 struct path *root = &ctx->root;
305
306 if (capable(CAP_DAC_READ_SEARCH))
307 return 0;
308
309 /*
310 * Allow relaxed permissions of file handles if the caller has
311 * the ability to mount the filesystem or create a bind-mount of
312 * the provided @mountdirfd.
313 *
314 * In both cases the caller may be able to get an unobstructed
315 * way to the encoded file handle. If the caller is only able to
316 * create a bind-mount we need to verify that there are no
317 * locked mounts on top of it that could prevent us from getting
318 * to the encoded file.
319 *
320 * In principle, locked mounts can prevent the caller from
321 * mounting the filesystem but that only applies to procfs and
322 * sysfs neither of which support decoding file handles.
323 *
324 * Restrict to O_DIRECTORY to provide a deterministic API that
325 * avoids a confusing api in the face of disconnected non-dir
326 * dentries.
327 *
328 * There's only one dentry for each directory inode (VFS rule)...
329 */
330 if (!(o_flags & O_DIRECTORY))
331 return -EPERM;
332
333 if (ns_capable(root->mnt->mnt_sb->s_user_ns, CAP_SYS_ADMIN))
334 ctx->flags = HANDLE_CHECK_PERMS;
335 else if (is_mounted(root->mnt) &&
336 capable_wrt_mount(real_mount(root->mnt)) &&
337 !has_locked_children(real_mount(root->mnt), root->dentry))
338 ctx->flags = HANDLE_CHECK_PERMS | HANDLE_CHECK_SUBTREE;
339 else
340 return -EPERM;
341
342 /* Are we able to override DAC permissions? */
343 if (!ns_capable(current_user_ns(), CAP_DAC_READ_SEARCH))
344 return -EPERM;
345
346 ctx->fh_flags = EXPORT_FH_DIR_ONLY;
347 return 0;
348 }
349
handle_to_path(int mountdirfd,struct file_handle __user * ufh,struct path * path,unsigned int o_flags)350 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
351 struct path *path, unsigned int o_flags)
352 {
353 int retval = 0;
354 struct file_handle f_handle;
355 struct file_handle *handle __free(kfree) = NULL;
356 struct handle_to_path_ctx ctx = {};
357 const struct export_operations *eops;
358
359 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
360 return -EFAULT;
361
362 if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
363 (f_handle.handle_bytes == 0))
364 return -EINVAL;
365
366 if (f_handle.handle_type < 0 ||
367 FILEID_USER_FLAGS(f_handle.handle_type) & ~FILEID_VALID_USER_FLAGS)
368 return -EINVAL;
369
370 retval = get_path_anchor(mountdirfd, &ctx.root);
371 if (retval)
372 return retval;
373
374 eops = ctx.root.mnt->mnt_sb->s_export_op;
375 if (eops && eops->permission)
376 retval = eops->permission(&ctx, o_flags);
377 else
378 retval = may_decode_fh(&ctx, o_flags);
379 if (retval)
380 goto out_path;
381
382 handle = kmalloc_flex(*handle, f_handle, f_handle.handle_bytes);
383 if (!handle) {
384 retval = -ENOMEM;
385 goto out_path;
386 }
387 /* copy the full handle */
388 *handle = f_handle;
389 if (copy_from_user(&handle->f_handle,
390 &ufh->f_handle,
391 f_handle.handle_bytes)) {
392 retval = -EFAULT;
393 goto out_path;
394 }
395
396 /*
397 * If handle was encoded with AT_HANDLE_CONNECTABLE, verify that we
398 * are decoding an fd with connected path, which is accessible from
399 * the mount fd path.
400 */
401 if (f_handle.handle_type & FILEID_IS_CONNECTABLE) {
402 ctx.fh_flags |= EXPORT_FH_CONNECTABLE;
403 ctx.flags |= HANDLE_CHECK_SUBTREE;
404 }
405 if (f_handle.handle_type & FILEID_IS_DIR)
406 ctx.fh_flags |= EXPORT_FH_DIR_ONLY;
407 /* Filesystem code should not be exposed to user flags */
408 handle->handle_type &= ~FILEID_USER_FLAGS_MASK;
409 retval = do_handle_to_path(handle, path, &ctx);
410
411 out_path:
412 path_put(&ctx.root);
413 return retval;
414 }
415
file_open_handle(struct path * path,int open_flag)416 static struct file *file_open_handle(struct path *path, int open_flag)
417 {
418 const struct export_operations *eops;
419
420 eops = path->mnt->mnt_sb->s_export_op;
421 if (eops->open)
422 return eops->open(path, open_flag);
423
424 return file_open_root(path, "", open_flag, 0);
425 }
426
do_handle_open(int mountdirfd,struct file_handle __user * ufh,int open_flag)427 static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
428 int open_flag)
429 {
430 long retval;
431 struct path path __free(path_put) = {};
432
433 retval = handle_to_path(mountdirfd, ufh, &path, open_flag);
434 if (retval)
435 return retval;
436
437 return FD_ADD(open_flag, file_open_handle(&path, open_flag));
438 }
439
440 /**
441 * sys_open_by_handle_at: Open the file handle
442 * @mountdirfd: directory file descriptor
443 * @handle: file handle to be opened
444 * @flags: open flags.
445 *
446 * @mountdirfd indicate the directory file descriptor
447 * of the mount point. file handle is decoded relative
448 * to the vfsmount pointed by the @mountdirfd. @flags
449 * value is same as the open(2) flags.
450 */
SYSCALL_DEFINE3(open_by_handle_at,int,mountdirfd,struct file_handle __user *,handle,int,flags)451 SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
452 struct file_handle __user *, handle,
453 int, flags)
454 {
455 long ret;
456
457 if (force_o_largefile())
458 flags |= O_LARGEFILE;
459
460 ret = do_handle_open(mountdirfd, handle, flags);
461 return ret;
462 }
463
464 #ifdef CONFIG_COMPAT
465 /*
466 * Exactly like fs/open.c:sys_open_by_handle_at(), except that it
467 * doesn't set the O_LARGEFILE flag.
468 */
COMPAT_SYSCALL_DEFINE3(open_by_handle_at,int,mountdirfd,struct file_handle __user *,handle,int,flags)469 COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
470 struct file_handle __user *, handle, int, flags)
471 {
472 return do_handle_open(mountdirfd, handle, flags);
473 }
474 #endif
475