UBIFS: use anonymous device

UBIFS has erroneuosly set 'sb->s_dev' to the UBI volume
character device major/minor. This may lead to clashes
if there is another FS mounted to a block device with
the same major/minor numbers. User-space programs which
use 'stat->st_dev' may get confused because of this.

This problem was found by Al Viro. He also pointed the
way to fix the problem - use 'set_anon_super()' and
'kill_anon_super()' VFS helpers.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/super.c

@@ -1945,7 +1945,6 @@ static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_magic = UBIFS_SUPER_MAGIC;
 	sb->s_blocksize = UBIFS_BLOCK_SIZE;
 	sb->s_blocksize_bits = UBIFS_BLOCK_SHIFT;
-	sb->s_dev = c->vi.cdev;
 	sb->s_maxbytes = c->max_inode_sz = key_max_inode_size(c);
 	if (c->max_inode_sz > MAX_LFS_FILESIZE)
 		sb->s_maxbytes = c->max_inode_sz = MAX_LFS_FILESIZE;
@@ -1990,16 +1989,9 @@ static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
 static int sb_test(struct super_block *sb, void *data)
 {
 	dev_t *dev = data;
+	struct ubifs_info *c = sb->s_fs_info;
 
-	return sb->s_dev == *dev;
-}
-
-static int sb_set(struct super_block *sb, void *data)
-{
-	dev_t *dev = data;
-
-	sb->s_dev = *dev;
-	return 0;
+	return c->vi.cdev == *dev;
 }
 
 static int ubifs_get_sb(struct file_system_type *fs_type, int flags,
@@ -2027,7 +2019,7 @@ static int ubifs_get_sb(struct file_system_type *fs_type, int flags,
 
 	dbg_gen("opened ubi%d_%d", vi.ubi_num, vi.vol_id);
 
-	sb = sget(fs_type, &sb_test, &sb_set, &vi.cdev);
+	sb = sget(fs_type, &sb_test, &set_anon_super, &vi.cdev);
 	if (IS_ERR(sb)) {
 		err = PTR_ERR(sb);
 		goto out_close;
@@ -2068,16 +2060,11 @@ static int ubifs_get_sb(struct file_system_type *fs_type, int flags,
 	return err;
 }
 
-static void ubifs_kill_sb(struct super_block *sb)
-{
-	generic_shutdown_super(sb);
-}
-
 static struct file_system_type ubifs_fs_type = {
 	.name    = "ubifs",
 	.owner   = THIS_MODULE,
 	.get_sb  = ubifs_get_sb,
-	.kill_sb = ubifs_kill_sb
+	.kill_sb = kill_anon_super,
 };
 
 /*