Root/fs/fhandle.c

1#include <linux/syscalls.h>
2#include <linux/slab.h>
3#include <linux/fs.h>
4#include <linux/file.h>
5#include <linux/mount.h>
6#include <linux/namei.h>
7#include <linux/exportfs.h>
8#include <linux/fs_struct.h>
9#include <linux/fsnotify.h>
10#include <linux/personality.h>
11#include <asm/uaccess.h>
12#include "internal.h"
13
14static long do_sys_name_to_handle(struct path *path,
15                  struct file_handle __user *ufh,
16                  int __user *mnt_id)
17{
18    long retval;
19    struct file_handle f_handle;
20    int handle_dwords, handle_bytes;
21    struct file_handle *handle = NULL;
22
23    /*
24     * We need t make sure wether the file system
25     * support decoding of the file handle
26     */
27    if (!path->mnt->mnt_sb->s_export_op ||
28        !path->mnt->mnt_sb->s_export_op->fh_to_dentry)
29        return -EOPNOTSUPP;
30
31    if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
32        return -EFAULT;
33
34    if (f_handle.handle_bytes > MAX_HANDLE_SZ)
35        return -EINVAL;
36
37    handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
38             GFP_KERNEL);
39    if (!handle)
40        return -ENOMEM;
41
42    /* convert handle size to multiple of sizeof(u32) */
43    handle_dwords = f_handle.handle_bytes >> 2;
44
45    /* we ask for a non connected handle */
46    retval = exportfs_encode_fh(path->dentry,
47                    (struct fid *)handle->f_handle,
48                    &handle_dwords, 0);
49    handle->handle_type = retval;
50    /* convert handle size to bytes */
51    handle_bytes = handle_dwords * sizeof(u32);
52    handle->handle_bytes = handle_bytes;
53    if ((handle->handle_bytes > f_handle.handle_bytes) ||
54        (retval == 255) || (retval == -ENOSPC)) {
55        /* As per old exportfs_encode_fh documentation
56         * we could return ENOSPC to indicate overflow
57         * But file system returned 255 always. So handle
58         * both the values
59         */
60        /*
61         * set the handle size to zero so we copy only
62         * non variable part of the file_handle
63         */
64        handle_bytes = 0;
65        retval = -EOVERFLOW;
66    } else
67        retval = 0;
68    /* copy the mount id */
69    if (copy_to_user(mnt_id, &path->mnt->mnt_id, sizeof(*mnt_id)) ||
70        copy_to_user(ufh, handle,
71             sizeof(struct file_handle) + handle_bytes))
72        retval = -EFAULT;
73    kfree(handle);
74    return retval;
75}
76
77/**
78 * sys_name_to_handle_at: convert name to handle
79 * @dfd: directory relative to which name is interpreted if not absolute
80 * @name: name that should be converted to handle.
81 * @handle: resulting file handle
82 * @mnt_id: mount id of the file system containing the file
83 * @flag: flag value to indicate whether to follow symlink or not
84 *
85 * @handle->handle_size indicate the space available to store the
86 * variable part of the file handle in bytes. If there is not
87 * enough space, the field is updated to return the minimum
88 * value required.
89 */
90SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
91        struct file_handle __user *, handle, int __user *, mnt_id,
92        int, flag)
93{
94    struct path path;
95    int lookup_flags;
96    int err;
97
98    if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
99        return -EINVAL;
100
101    lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
102    if (flag & AT_EMPTY_PATH)
103        lookup_flags |= LOOKUP_EMPTY;
104    err = user_path_at(dfd, name, lookup_flags, &path);
105    if (!err) {
106        err = do_sys_name_to_handle(&path, handle, mnt_id);
107        path_put(&path);
108    }
109    return err;
110}
111
112static struct vfsmount *get_vfsmount_from_fd(int fd)
113{
114    struct path path;
115
116    if (fd == AT_FDCWD) {
117        struct fs_struct *fs = current->fs;
118        spin_lock(&fs->lock);
119        path = fs->pwd;
120        mntget(path.mnt);
121        spin_unlock(&fs->lock);
122    } else {
123        int fput_needed;
124        struct file *file = fget_light(fd, &fput_needed);
125        if (!file)
126            return ERR_PTR(-EBADF);
127        path = file->f_path;
128        mntget(path.mnt);
129        fput_light(file, fput_needed);
130    }
131    return path.mnt;
132}
133
134static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
135{
136    return 1;
137}
138
139static 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;
161out_mnt:
162    mntput(path->mnt);
163out_err:
164    return retval;
165}
166
167static 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    if (copy_from_user(handle, ufh,
200               sizeof(struct file_handle) +
201               f_handle.handle_bytes)) {
202        retval = -EFAULT;
203        goto out_handle;
204    }
205
206    retval = do_handle_to_path(mountdirfd, handle, path);
207
208out_handle:
209    kfree(handle);
210out_err:
211    return retval;
212}
213
214long do_handle_open(int mountdirfd,
215            struct file_handle __user *ufh, int open_flag)
216{
217    long retval = 0;
218    struct path path;
219    struct file *file;
220    int fd;
221
222    retval = handle_to_path(mountdirfd, ufh, &path);
223    if (retval)
224        return retval;
225
226    fd = get_unused_fd_flags(open_flag);
227    if (fd < 0) {
228        path_put(&path);
229        return fd;
230    }
231    file = file_open_root(path.dentry, path.mnt, "", open_flag);
232    if (IS_ERR(file)) {
233        put_unused_fd(fd);
234        retval = PTR_ERR(file);
235    } else {
236        retval = fd;
237        fsnotify_open(file);
238        fd_install(fd, file);
239    }
240    path_put(&path);
241    return retval;
242}
243
244/**
245 * sys_open_by_handle_at: Open the file handle
246 * @mountdirfd: directory file descriptor
247 * @handle: file handle to be opened
248 * @flag: open flags.
249 *
250 * @mountdirfd indicate the directory file descriptor
251 * of the mount point. file handle is decoded relative
252 * to the vfsmount pointed by the @mountdirfd. @flags
253 * value is same as the open(2) flags.
254 */
255SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
256        struct file_handle __user *, handle,
257        int, flags)
258{
259    long ret;
260
261    if (force_o_largefile())
262        flags |= O_LARGEFILE;
263
264    ret = do_handle_open(mountdirfd, handle, flags);
265    return ret;
266}
267

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