xref: /openbmc/linux/fs/fhandle.c (revision f2f4bf5a)
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  
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   */
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  
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  
134  static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
135  {
136  	return 1;
137  }
138  
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  
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  
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   */
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   */
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