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Linux/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 <linux/uaccess.h>
 12 #include "internal.h"
 13 #include "mount.h"
 14 
 15 static long do_sys_name_to_handle(struct path *path,
 16                                   struct file_handle __user *ufh,
 17                                   int __user *mnt_id)
 18 {
 19         long retval;
 20         struct file_handle f_handle;
 21         int handle_dwords, handle_bytes;
 22         struct file_handle *handle = NULL;
 23 
 24         /*
 25          * We need to make sure whether the file system
 26          * support decoding of the file handle
 27          */
 28         if (!path->dentry->d_sb->s_export_op ||
 29             !path->dentry->d_sb->s_export_op->fh_to_dentry)
 30                 return -EOPNOTSUPP;
 31 
 32         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
 33                 return -EFAULT;
 34 
 35         if (f_handle.handle_bytes > MAX_HANDLE_SZ)
 36                 return -EINVAL;
 37 
 38         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
 39                          GFP_KERNEL);
 40         if (!handle)
 41                 return -ENOMEM;
 42 
 43         /* convert handle size to multiple of sizeof(u32) */
 44         handle_dwords = f_handle.handle_bytes >> 2;
 45 
 46         /* we ask for a non connected handle */
 47         retval = exportfs_encode_fh(path->dentry,
 48                                     (struct fid *)handle->f_handle,
 49                                     &handle_dwords,  0);
 50         handle->handle_type = retval;
 51         /* convert handle size to bytes */
 52         handle_bytes = handle_dwords * sizeof(u32);
 53         handle->handle_bytes = handle_bytes;
 54         if ((handle->handle_bytes > f_handle.handle_bytes) ||
 55             (retval == FILEID_INVALID) || (retval == -ENOSPC)) {
 56                 /* As per old exportfs_encode_fh documentation
 57                  * we could return ENOSPC to indicate overflow
 58                  * But file system returned 255 always. So handle
 59                  * both the values
 60                  */
 61                 /*
 62                  * set the handle size to zero so we copy only
 63                  * non variable part of the file_handle
 64                  */
 65                 handle_bytes = 0;
 66                 retval = -EOVERFLOW;
 67         } else
 68                 retval = 0;
 69         /* copy the mount id */
 70         if (copy_to_user(mnt_id, &real_mount(path->mnt)->mnt_id,
 71                          sizeof(*mnt_id)) ||
 72             copy_to_user(ufh, handle,
 73                          sizeof(struct file_handle) + handle_bytes))
 74                 retval = -EFAULT;
 75         kfree(handle);
 76         return retval;
 77 }
 78 
 79 /**
 80  * sys_name_to_handle_at: convert name to handle
 81  * @dfd: directory relative to which name is interpreted if not absolute
 82  * @name: name that should be converted to handle.
 83  * @handle: resulting file handle
 84  * @mnt_id: mount id of the file system containing the file
 85  * @flag: flag value to indicate whether to follow symlink or not
 86  *
 87  * @handle->handle_size indicate the space available to store the
 88  * variable part of the file handle in bytes. If there is not
 89  * enough space, the field is updated to return the minimum
 90  * value required.
 91  */
 92 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
 93                 struct file_handle __user *, handle, int __user *, mnt_id,
 94                 int, flag)
 95 {
 96         struct path path;
 97         int lookup_flags;
 98         int err;
 99 
100         if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
101                 return -EINVAL;
102 
103         lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
104         if (flag & AT_EMPTY_PATH)
105                 lookup_flags |= LOOKUP_EMPTY;
106         err = user_path_at(dfd, name, lookup_flags, &path);
107         if (!err) {
108                 err = do_sys_name_to_handle(&path, handle, mnt_id);
109                 path_put(&path);
110         }
111         return err;
112 }
113 
114 static struct vfsmount *get_vfsmount_from_fd(int fd)
115 {
116         struct vfsmount *mnt;
117 
118         if (fd == AT_FDCWD) {
119                 struct fs_struct *fs = current->fs;
120                 spin_lock(&fs->lock);
121                 mnt = mntget(fs->pwd.mnt);
122                 spin_unlock(&fs->lock);
123         } else {
124                 struct fd f = fdget(fd);
125                 if (!f.file)
126                         return ERR_PTR(-EBADF);
127                 mnt = mntget(f.file->f_path.mnt);
128                 fdput(f);
129         }
130         return mnt;
131 }
132 
133 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
134 {
135         return 1;
136 }
137 
138 static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
139                              struct path *path)
140 {
141         int retval = 0;
142         int handle_dwords;
143 
144         path->mnt = get_vfsmount_from_fd(mountdirfd);
145         if (IS_ERR(path->mnt)) {
146                 retval = PTR_ERR(path->mnt);
147                 goto out_err;
148         }
149         /* change the handle size to multiple of sizeof(u32) */
150         handle_dwords = handle->handle_bytes >> 2;
151         path->dentry = exportfs_decode_fh(path->mnt,
152                                           (struct fid *)handle->f_handle,
153                                           handle_dwords, handle->handle_type,
154                                           vfs_dentry_acceptable, NULL);
155         if (IS_ERR(path->dentry)) {
156                 retval = PTR_ERR(path->dentry);
157                 goto out_mnt;
158         }
159         return 0;
160 out_mnt:
161         mntput(path->mnt);
162 out_err:
163         return retval;
164 }
165 
166 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
167                    struct path *path)
168 {
169         int retval = 0;
170         struct file_handle f_handle;
171         struct file_handle *handle = NULL;
172 
173         /*
174          * With handle we don't look at the execute bit on the
175          * the directory. Ideally we would like CAP_DAC_SEARCH.
176          * But we don't have that
177          */
178         if (!capable(CAP_DAC_READ_SEARCH)) {
179                 retval = -EPERM;
180                 goto out_err;
181         }
182         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
183                 retval = -EFAULT;
184                 goto out_err;
185         }
186         if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
187             (f_handle.handle_bytes == 0)) {
188                 retval = -EINVAL;
189                 goto out_err;
190         }
191         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
192                          GFP_KERNEL);
193         if (!handle) {
194                 retval = -ENOMEM;
195                 goto out_err;
196         }
197         /* copy the full handle */
198         *handle = f_handle;
199         if (copy_from_user(&handle->f_handle,
200                            &ufh->f_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 
208 out_handle:
209         kfree(handle);
210 out_err:
211         return retval;
212 }
213 
214 long 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, 0);
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  */
255 SYSCALL_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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