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