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