ubi: Don't bypass ->getattr()

Directly accessing inode fields bypasses ->getattr()
and can cause problems when the underlying filesystem
does not have the default ->getattr() implementation.

So instead of obtaining the backing inode via d_backing_inode()
use vfs_getattr() and obtain what we need from the kstat struct.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/build.c

@@ -1147,22 +1147,26 @@ int ubi_detach_mtd_dev(int ubi_num, int anyway)
  */
 static struct mtd_info * __init open_mtd_by_chdev(const char *mtd_dev)
 {
-	int err, major, minor, mode;
+	int err, minor;
 	struct path path;
+	struct kstat stat;
 
 	/* Probably this is an MTD character device node path */
 	err = kern_path(mtd_dev, LOOKUP_FOLLOW, &path);
 	if (err)
 		return ERR_PTR(err);
 
-	/* MTD device number is defined by the major / minor numbers */
-	major = imajor(d_backing_inode(path.dentry));
-	minor = iminor(d_backing_inode(path.dentry));
-	mode = d_backing_inode(path.dentry)->i_mode;
+	err = vfs_getattr(&path, &stat);
 	path_put(&path);
-	if (major != MTD_CHAR_MAJOR || !S_ISCHR(mode))
+	if (err)
+		return ERR_PTR(err);
+
+	/* MTD device number is defined by the major / minor numbers */
+	if (MAJOR(stat.rdev) != MTD_CHAR_MAJOR || !S_ISCHR(stat.mode))
 		return ERR_PTR(-EINVAL);
 
+	minor = MINOR(stat.rdev);
+
 	if (minor & 1)
 		/*
 		 * Just do not think the "/dev/mtdrX" devices support is need,

drivers/mtd/ubi/kapi.c

@@ -301,9 +301,9 @@ EXPORT_SYMBOL_GPL(ubi_open_volume_nm);
  */
 struct ubi_volume_desc *ubi_open_volume_path(const char *pathname, int mode)
 {
-	int error, ubi_num, vol_id, mod;
-	struct inode *inode;
+	int error, ubi_num, vol_id;
 	struct path path;
+	struct kstat stat;
 
 	dbg_gen("open volume %s, mode %d", pathname, mode);
 
@@ -314,14 +314,17 @@ struct ubi_volume_desc *ubi_open_volume_path(const char *pathname, int mode)
 	if (error)
 		return ERR_PTR(error);
 
-	inode = d_backing_inode(path.dentry);
-	mod = inode->i_mode;
-	ubi_num = ubi_major2num(imajor(inode));
-	vol_id = iminor(inode) - 1;
+	error = vfs_getattr(&path, &stat);
 	path_put(&path);
+	if (error)
+		return ERR_PTR(error);
 
-	if (!S_ISCHR(mod))
+	if (!S_ISCHR(stat.mode))
 		return ERR_PTR(-EINVAL);
+
+	ubi_num = ubi_major2num(MAJOR(stat.rdev));
+	vol_id = MINOR(stat.rdev) - 1;
+
 	if (vol_id >= 0 && ubi_num >= 0)
 		return ubi_open_volume(ubi_num, vol_id, mode);
 	return ERR_PTR(-ENODEV);