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,int __user * mnt_id,int fh_flags)17 static long do_sys_name_to_handle(const struct path *path,
18 struct file_handle __user *ufh,
19 int __user *mnt_id, int fh_flags)
20 {
21 long retval;
22 struct file_handle f_handle;
23 int handle_dwords, handle_bytes;
24 struct file_handle *handle = NULL;
25
26 /*
27 * We need to make sure whether the file system support decoding of
28 * the file handle if decodeable file handle was requested.
29 * Otherwise, even empty export_operations are sufficient to opt-in
30 * to encoding FIDs.
31 */
32 if (!path->dentry->d_sb->s_export_op ||
33 (!(fh_flags & EXPORT_FH_FID) &&
34 !path->dentry->d_sb->s_export_op->fh_to_dentry))
35 return -EOPNOTSUPP;
36
37 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
38 return -EFAULT;
39
40 if (f_handle.handle_bytes > MAX_HANDLE_SZ)
41 return -EINVAL;
42
43 handle = kzalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
44 GFP_KERNEL);
45 if (!handle)
46 return -ENOMEM;
47
48 /* convert handle size to multiple of sizeof(u32) */
49 handle_dwords = f_handle.handle_bytes >> 2;
50
51 /* we ask for a non connectable maybe decodeable file handle */
52 retval = exportfs_encode_fh(path->dentry,
53 (struct fid *)handle->f_handle,
54 &handle_dwords, fh_flags);
55 handle->handle_type = retval;
56 /* convert handle size to bytes */
57 handle_bytes = handle_dwords * sizeof(u32);
58 handle->handle_bytes = handle_bytes;
59 if ((handle->handle_bytes > f_handle.handle_bytes) ||
60 (retval == FILEID_INVALID) || (retval < 0)) {
61 /* As per old exportfs_encode_fh documentation
62 * we could return ENOSPC to indicate overflow
63 * But file system returned 255 always. So handle
64 * both the values
65 */
66 if (retval == FILEID_INVALID || retval == -ENOSPC)
67 retval = -EOVERFLOW;
68 /*
69 * set the handle size to zero so we copy only
70 * non variable part of the file_handle
71 */
72 handle_bytes = 0;
73 } else
74 retval = 0;
75 /* copy the mount id */
76 if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) ||
77 copy_to_user(ufh, handle,
78 struct_size(handle, f_handle, handle_bytes)))
79 retval = -EFAULT;
80 kfree(handle);
81 return retval;
82 }
83
84 /**
85 * sys_name_to_handle_at: convert name to handle
86 * @dfd: directory relative to which name is interpreted if not absolute
87 * @name: name that should be converted to handle.
88 * @handle: resulting file handle
89 * @mnt_id: mount id of the file system containing the file
90 * @flag: flag value to indicate whether to follow symlink or not
91 * and whether a decodable file handle is required.
92 *
93 * @handle->handle_size indicate the space available to store the
94 * variable part of the file handle in bytes. If there is not
95 * enough space, the field is updated to return the minimum
96 * value required.
97 */
SYSCALL_DEFINE5(name_to_handle_at,int,dfd,const char __user *,name,struct file_handle __user *,handle,int __user *,mnt_id,int,flag)98 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
99 struct file_handle __user *, handle, int __user *, mnt_id,
100 int, flag)
101 {
102 struct path path;
103 int lookup_flags;
104 int fh_flags;
105 int err;
106
107 if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID))
108 return -EINVAL;
109
110 lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
111 fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0;
112 if (flag & AT_EMPTY_PATH)
113 lookup_flags |= LOOKUP_EMPTY;
114 err = user_path_at(dfd, name, lookup_flags, &path);
115 if (!err) {
116 err = do_sys_name_to_handle(&path, handle, mnt_id, fh_flags);
117 path_put(&path);
118 }
119 return err;
120 }
121
get_vfsmount_from_fd(int fd)122 static struct vfsmount *get_vfsmount_from_fd(int fd)
123 {
124 struct vfsmount *mnt;
125
126 if (fd == AT_FDCWD) {
127 struct fs_struct *fs = current->fs;
128 spin_lock(&fs->lock);
129 mnt = mntget(fs->pwd.mnt);
130 spin_unlock(&fs->lock);
131 } else {
132 struct fd f = fdget(fd);
133 if (!f.file)
134 return ERR_PTR(-EBADF);
135 mnt = mntget(f.file->f_path.mnt);
136 fdput(f);
137 }
138 return mnt;
139 }
140
vfs_dentry_acceptable(void * context,struct dentry * dentry)141 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
142 {
143 return 1;
144 }
145
do_handle_to_path(int mountdirfd,struct file_handle * handle,struct path * path)146 static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
147 struct path *path)
148 {
149 int retval = 0;
150 int handle_dwords;
151
152 path->mnt = get_vfsmount_from_fd(mountdirfd);
153 if (IS_ERR(path->mnt)) {
154 retval = PTR_ERR(path->mnt);
155 goto out_err;
156 }
157 /* change the handle size to multiple of sizeof(u32) */
158 handle_dwords = handle->handle_bytes >> 2;
159 path->dentry = exportfs_decode_fh(path->mnt,
160 (struct fid *)handle->f_handle,
161 handle_dwords, handle->handle_type,
162 vfs_dentry_acceptable, NULL);
163 if (IS_ERR(path->dentry)) {
164 retval = PTR_ERR(path->dentry);
165 goto out_mnt;
166 }
167 return 0;
168 out_mnt:
169 mntput(path->mnt);
170 out_err:
171 return retval;
172 }
173
handle_to_path(int mountdirfd,struct file_handle __user * ufh,struct path * path)174 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
175 struct path *path)
176 {
177 int retval = 0;
178 struct file_handle f_handle;
179 struct file_handle *handle = NULL;
180
181 /*
182 * With handle we don't look at the execute bit on the
183 * directory. Ideally we would like CAP_DAC_SEARCH.
184 * But we don't have that
185 */
186 if (!capable(CAP_DAC_READ_SEARCH)) {
187 retval = -EPERM;
188 goto out_err;
189 }
190 if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
191 retval = -EFAULT;
192 goto out_err;
193 }
194 if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
195 (f_handle.handle_bytes == 0)) {
196 retval = -EINVAL;
197 goto out_err;
198 }
199 handle = kmalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
200 GFP_KERNEL);
201 if (!handle) {
202 retval = -ENOMEM;
203 goto out_err;
204 }
205 /* copy the full handle */
206 *handle = f_handle;
207 if (copy_from_user(&handle->f_handle,
208 &ufh->f_handle,
209 f_handle.handle_bytes)) {
210 retval = -EFAULT;
211 goto out_handle;
212 }
213
214 retval = do_handle_to_path(mountdirfd, handle, path);
215
216 out_handle:
217 kfree(handle);
218 out_err:
219 return retval;
220 }
221
do_handle_open(int mountdirfd,struct file_handle __user * ufh,int open_flag)222 static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
223 int open_flag)
224 {
225 long retval = 0;
226 struct path path;
227 struct file *file;
228 int fd;
229
230 retval = handle_to_path(mountdirfd, ufh, &path);
231 if (retval)
232 return retval;
233
234 fd = get_unused_fd_flags(open_flag);
235 if (fd < 0) {
236 path_put(&path);
237 return fd;
238 }
239 file = file_open_root(&path, "", open_flag, 0);
240 if (IS_ERR(file)) {
241 put_unused_fd(fd);
242 retval = PTR_ERR(file);
243 } else {
244 retval = fd;
245 fd_install(fd, file);
246 }
247 path_put(&path);
248 return retval;
249 }
250
251 /**
252 * sys_open_by_handle_at: Open the file handle
253 * @mountdirfd: directory file descriptor
254 * @handle: file handle to be opened
255 * @flags: open flags.
256 *
257 * @mountdirfd indicate the directory file descriptor
258 * of the mount point. file handle is decoded relative
259 * to the vfsmount pointed by the @mountdirfd. @flags
260 * value is same as the open(2) flags.
261 */
SYSCALL_DEFINE3(open_by_handle_at,int,mountdirfd,struct file_handle __user *,handle,int,flags)262 SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
263 struct file_handle __user *, handle,
264 int, flags)
265 {
266 long ret;
267
268 if (force_o_largefile())
269 flags |= O_LARGEFILE;
270
271 ret = do_handle_open(mountdirfd, handle, flags);
272 return ret;
273 }
274
275 #ifdef CONFIG_COMPAT
276 /*
277 * Exactly like fs/open.c:sys_open_by_handle_at(), except that it
278 * doesn't set the O_LARGEFILE flag.
279 */
COMPAT_SYSCALL_DEFINE3(open_by_handle_at,int,mountdirfd,struct file_handle __user *,handle,int,flags)280 COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
281 struct file_handle __user *, handle, int, flags)
282 {
283 return do_handle_open(mountdirfd, handle, flags);
284 }
285 #endif
286