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
do_sys_name_to_handle(const struct path * path,struct file_handle __user * ufh,void __user * mnt_id,bool unique_mntid,int fh_flags)17 static 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 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
35 return -EFAULT;
36
37 if (f_handle.handle_bytes > MAX_HANDLE_SZ)
38 return -EINVAL;
39
40 handle = kzalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
41 GFP_KERNEL);
42 if (!handle)
43 return -ENOMEM;
44
45 /* convert handle size to multiple of sizeof(u32) */
46 handle_dwords = f_handle.handle_bytes >> 2;
47
48 /* we ask for a non connectable maybe decodeable file handle */
49 retval = exportfs_encode_fh(path->dentry,
50 (struct fid *)handle->f_handle,
51 &handle_dwords, fh_flags);
52 handle->handle_type = retval;
53 /* convert handle size to bytes */
54 handle_bytes = handle_dwords * sizeof(u32);
55 handle->handle_bytes = handle_bytes;
56 if ((handle->handle_bytes > f_handle.handle_bytes) ||
57 (retval == FILEID_INVALID) || (retval < 0)) {
58 /* As per old exportfs_encode_fh documentation
59 * we could return ENOSPC to indicate overflow
60 * But file system returned 255 always. So handle
61 * both the values
62 */
63 if (retval == FILEID_INVALID || retval == -ENOSPC)
64 retval = -EOVERFLOW;
65 /*
66 * set the handle size to zero so we copy only
67 * non variable part of the file_handle
68 */
69 handle_bytes = 0;
70 } else
71 retval = 0;
72 /* copy the mount id */
73 if (unique_mntid) {
74 if (put_user(real_mount(path->mnt)->mnt_id_unique,
75 (u64 __user *) mnt_id))
76 retval = -EFAULT;
77 } else {
78 if (put_user(real_mount(path->mnt)->mnt_id,
79 (int __user *) mnt_id))
80 retval = -EFAULT;
81 }
82 /* copy the handle */
83 if (retval != -EFAULT &&
84 copy_to_user(ufh, handle,
85 struct_size(handle, f_handle, handle_bytes)))
86 retval = -EFAULT;
87 kfree(handle);
88 return retval;
89 }
90
91 /**
92 * sys_name_to_handle_at: convert name to handle
93 * @dfd: directory relative to which name is interpreted if not absolute
94 * @name: name that should be converted to handle.
95 * @handle: resulting file handle
96 * @mnt_id: mount id of the file system containing the file
97 * (u64 if AT_HANDLE_MNT_ID_UNIQUE, otherwise int)
98 * @flag: flag value to indicate whether to follow symlink or not
99 * and whether a decodable file handle is required.
100 *
101 * @handle->handle_size indicate the space available to store the
102 * variable part of the file handle in bytes. If there is not
103 * enough space, the field is updated to return the minimum
104 * value required.
105 */
SYSCALL_DEFINE5(name_to_handle_at,int,dfd,const char __user *,name,struct file_handle __user *,handle,void __user *,mnt_id,int,flag)106 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
107 struct file_handle __user *, handle, void __user *, mnt_id,
108 int, flag)
109 {
110 struct path path;
111 int lookup_flags;
112 int fh_flags;
113 int err;
114
115 if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID |
116 AT_HANDLE_MNT_ID_UNIQUE))
117 return -EINVAL;
118
119 lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
120 fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0;
121 if (flag & AT_EMPTY_PATH)
122 lookup_flags |= LOOKUP_EMPTY;
123 err = user_path_at(dfd, name, lookup_flags, &path);
124 if (!err) {
125 err = do_sys_name_to_handle(&path, handle, mnt_id,
126 flag & AT_HANDLE_MNT_ID_UNIQUE,
127 fh_flags);
128 path_put(&path);
129 }
130 return err;
131 }
132
get_path_from_fd(int fd,struct path * root)133 static int get_path_from_fd(int fd, struct path *root)
134 {
135 if (fd == AT_FDCWD) {
136 struct fs_struct *fs = current->fs;
137 spin_lock(&fs->lock);
138 *root = fs->pwd;
139 path_get(root);
140 spin_unlock(&fs->lock);
141 } else {
142 struct fd f = fdget(fd);
143 if (!fd_file(f))
144 return -EBADF;
145 *root = fd_file(f)->f_path;
146 path_get(root);
147 fdput(f);
148 }
149
150 return 0;
151 }
152
153 enum handle_to_path_flags {
154 HANDLE_CHECK_PERMS = (1 << 0),
155 HANDLE_CHECK_SUBTREE = (1 << 1),
156 };
157
158 struct handle_to_path_ctx {
159 struct path root;
160 enum handle_to_path_flags flags;
161 unsigned int fh_flags;
162 };
163
vfs_dentry_acceptable(void * context,struct dentry * dentry)164 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
165 {
166 struct handle_to_path_ctx *ctx = context;
167 struct user_namespace *user_ns = current_user_ns();
168 struct dentry *d, *root = ctx->root.dentry;
169 struct mnt_idmap *idmap = mnt_idmap(ctx->root.mnt);
170 int retval = 0;
171
172 if (!root)
173 return 1;
174
175 /* Old permission model with global CAP_DAC_READ_SEARCH. */
176 if (!ctx->flags)
177 return 1;
178
179 /*
180 * It's racy as we're not taking rename_lock but we're able to ignore
181 * permissions and we just need an approximation whether we were able
182 * to follow a path to the file.
183 *
184 * It's also potentially expensive on some filesystems especially if
185 * there is a deep path.
186 */
187 d = dget(dentry);
188 while (d != root && !IS_ROOT(d)) {
189 struct dentry *parent = dget_parent(d);
190
191 /*
192 * We know that we have the ability to override DAC permissions
193 * as we've verified this earlier via CAP_DAC_READ_SEARCH. But
194 * we also need to make sure that there aren't any unmapped
195 * inodes in the path that would prevent us from reaching the
196 * file.
197 */
198 if (!privileged_wrt_inode_uidgid(user_ns, idmap,
199 d_inode(parent))) {
200 dput(d);
201 dput(parent);
202 return retval;
203 }
204
205 dput(d);
206 d = parent;
207 }
208
209 if (!(ctx->flags & HANDLE_CHECK_SUBTREE) || d == root)
210 retval = 1;
211 WARN_ON_ONCE(d != root && d != root->d_sb->s_root);
212 dput(d);
213 return retval;
214 }
215
do_handle_to_path(struct file_handle * handle,struct path * path,struct handle_to_path_ctx * ctx)216 static int do_handle_to_path(struct file_handle *handle, struct path *path,
217 struct handle_to_path_ctx *ctx)
218 {
219 int handle_dwords;
220 struct vfsmount *mnt = ctx->root.mnt;
221
222 /* change the handle size to multiple of sizeof(u32) */
223 handle_dwords = handle->handle_bytes >> 2;
224 path->dentry = exportfs_decode_fh_raw(mnt,
225 (struct fid *)handle->f_handle,
226 handle_dwords, handle->handle_type,
227 ctx->fh_flags,
228 vfs_dentry_acceptable, ctx);
229 if (IS_ERR_OR_NULL(path->dentry)) {
230 if (path->dentry == ERR_PTR(-ENOMEM))
231 return -ENOMEM;
232 return -ESTALE;
233 }
234 path->mnt = mntget(mnt);
235 return 0;
236 }
237
238 /*
239 * Allow relaxed permissions of file handles if the caller has the
240 * ability to mount the filesystem or create a bind-mount of the
241 * provided @mountdirfd.
242 *
243 * In both cases the caller may be able to get an unobstructed way to
244 * the encoded file handle. If the caller is only able to create a
245 * bind-mount we need to verify that there are no locked mounts on top
246 * of it that could prevent us from getting to the encoded file.
247 *
248 * In principle, locked mounts can prevent the caller from mounting the
249 * filesystem but that only applies to procfs and sysfs neither of which
250 * support decoding file handles.
251 */
may_decode_fh(struct handle_to_path_ctx * ctx,unsigned int o_flags)252 static inline bool may_decode_fh(struct handle_to_path_ctx *ctx,
253 unsigned int o_flags)
254 {
255 struct path *root = &ctx->root;
256
257 /*
258 * Restrict to O_DIRECTORY to provide a deterministic API that avoids a
259 * confusing api in the face of disconnected non-dir dentries.
260 *
261 * There's only one dentry for each directory inode (VFS rule)...
262 */
263 if (!(o_flags & O_DIRECTORY))
264 return false;
265
266 if (ns_capable(root->mnt->mnt_sb->s_user_ns, CAP_SYS_ADMIN))
267 ctx->flags = HANDLE_CHECK_PERMS;
268 else if (is_mounted(root->mnt) &&
269 ns_capable(real_mount(root->mnt)->mnt_ns->user_ns,
270 CAP_SYS_ADMIN) &&
271 !has_locked_children(real_mount(root->mnt), root->dentry))
272 ctx->flags = HANDLE_CHECK_PERMS | HANDLE_CHECK_SUBTREE;
273 else
274 return false;
275
276 /* Are we able to override DAC permissions? */
277 if (!ns_capable(current_user_ns(), CAP_DAC_READ_SEARCH))
278 return false;
279
280 ctx->fh_flags = EXPORT_FH_DIR_ONLY;
281 return true;
282 }
283
handle_to_path(int mountdirfd,struct file_handle __user * ufh,struct path * path,unsigned int o_flags)284 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
285 struct path *path, unsigned int o_flags)
286 {
287 int retval = 0;
288 struct file_handle f_handle;
289 struct file_handle *handle = NULL;
290 struct handle_to_path_ctx ctx = {};
291
292 retval = get_path_from_fd(mountdirfd, &ctx.root);
293 if (retval)
294 goto out_err;
295
296 if (!capable(CAP_DAC_READ_SEARCH) && !may_decode_fh(&ctx, o_flags)) {
297 retval = -EPERM;
298 goto out_path;
299 }
300
301 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
302 retval = -EFAULT;
303 goto out_path;
304 }
305 if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
306 (f_handle.handle_bytes == 0)) {
307 retval = -EINVAL;
308 goto out_path;
309 }
310 handle = kmalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
311 GFP_KERNEL);
312 if (!handle) {
313 retval = -ENOMEM;
314 goto out_path;
315 }
316 /* copy the full handle */
317 *handle = f_handle;
318 if (copy_from_user(&handle->f_handle,
319 &ufh->f_handle,
320 f_handle.handle_bytes)) {
321 retval = -EFAULT;
322 goto out_handle;
323 }
324
325 retval = do_handle_to_path(handle, path, &ctx);
326
327 out_handle:
328 kfree(handle);
329 out_path:
330 path_put(&ctx.root);
331 out_err:
332 return retval;
333 }
334
do_handle_open(int mountdirfd,struct file_handle __user * ufh,int open_flag)335 static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
336 int open_flag)
337 {
338 long retval = 0;
339 struct path path;
340 struct file *file;
341 int fd;
342
343 retval = handle_to_path(mountdirfd, ufh, &path, open_flag);
344 if (retval)
345 return retval;
346
347 fd = get_unused_fd_flags(open_flag);
348 if (fd < 0) {
349 path_put(&path);
350 return fd;
351 }
352 file = file_open_root(&path, "", open_flag, 0);
353 if (IS_ERR(file)) {
354 put_unused_fd(fd);
355 retval = PTR_ERR(file);
356 } else {
357 retval = fd;
358 fd_install(fd, file);
359 }
360 path_put(&path);
361 return retval;
362 }
363
364 /**
365 * sys_open_by_handle_at: Open the file handle
366 * @mountdirfd: directory file descriptor
367 * @handle: file handle to be opened
368 * @flags: open flags.
369 *
370 * @mountdirfd indicate the directory file descriptor
371 * of the mount point. file handle is decoded relative
372 * to the vfsmount pointed by the @mountdirfd. @flags
373 * value is same as the open(2) flags.
374 */
SYSCALL_DEFINE3(open_by_handle_at,int,mountdirfd,struct file_handle __user *,handle,int,flags)375 SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
376 struct file_handle __user *, handle,
377 int, flags)
378 {
379 long ret;
380
381 if (force_o_largefile())
382 flags |= O_LARGEFILE;
383
384 ret = do_handle_open(mountdirfd, handle, flags);
385 return ret;
386 }
387
388 #ifdef CONFIG_COMPAT
389 /*
390 * Exactly like fs/open.c:sys_open_by_handle_at(), except that it
391 * doesn't set the O_LARGEFILE flag.
392 */
COMPAT_SYSCALL_DEFINE3(open_by_handle_at,int,mountdirfd,struct file_handle __user *,handle,int,flags)393 COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
394 struct file_handle __user *, handle, int, flags)
395 {
396 return do_handle_open(mountdirfd, handle, flags);
397 }
398 #endif
399