ovl: Fix opaque regression in ovl_lookup

Current multi-layer support overlayfs has a regression in
.lookup(). If there is a directory in upperdir and a regular
file has same name in lowerdir in a merged directory, lower
file is hidden and upper directory is set to opaque in former
case. But it is changed in present code.

In lowerdir lookup path, if a found inode is not directory,
the type checking of previous inode is missing. This inode
will be copied to the lowerstack of ovl_entry directly.

That will lead to several wrong conditions, for example,
the reading of the directory in upperdir may return an error
like:

   ls: reading directory .: Not a directory

This patch makes the lowerdir lookup path check the opaque
for non-directory file too.
Signed-off-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/overlayfs/super.c

@@ -372,7 +372,6 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		bool opaque = false;
 		struct path lowerpath = poe->lowerstack[i];
 
-		opaque = false;
 		this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
 		err = PTR_ERR(this);
 		if (IS_ERR(this)) {
@@ -395,20 +394,24 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		 */
 		if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
 			opaque = true;
+
+		if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
+			     !S_ISDIR(this->d_inode->i_mode))) {
 			/*
-		 * If this is a non-directory then stop here.
-		 *
-		 * FIXME: check for opaqueness maybe better done in remove code.
+			 * FIXME: check for upper-opaqueness maybe better done
+			 * in remove code.
 			 */
-		if (!S_ISDIR(this->d_inode->i_mode)) {
-			opaque = true;
-		} else if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
-				    !S_ISDIR(this->d_inode->i_mode))) {
 			if (prev == upperdentry)
 				upperopaque = true;
 			dput(this);
 			break;
 		}
+		/*
+		 * If this is a non-directory then stop here.
+		 */
+		if (!S_ISDIR(this->d_inode->i_mode))
+			opaque = true;
+
 		stack[ctr].dentry = this;
 		stack[ctr].mnt = lowerpath.mnt;
 		ctr++;