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