From bf6ed41692a49bcbe70ab0629cfc5d207c78544c Mon Sep 17 00:00:00 2001
From: Xin LI <delphij@FreeBSD.org>
Date: Tue, 11 Jun 2019 22:21:29 +0000
Subject: [PATCH] Avoid out of boundary access when checking invalid long
 filenames.

Obtained from:	OpenBSD (dir.c,v 1.25)
MFC after:	3 days
---
 sbin/fsck_msdosfs/dir.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/sbin/fsck_msdosfs/dir.c b/sbin/fsck_msdosfs/dir.c
index e59536f6b5fc..e56bbf80c6bf 100644
--- a/sbin/fsck_msdosfs/dir.c
+++ b/sbin/fsck_msdosfs/dir.c
@@ -629,6 +629,15 @@ readDosDirSection(int f, struct bootblock *boot, struct fatEntry *fat,
 					vallfn = NULL;
 				}
 				lidx = *p & LRNOMASK;
+				if (lidx == 0) {
+					pwarn("invalid long name\n");
+					if (!invlfn) {
+						invlfn = vallfn;
+						invcl = valcl;
+					}
+					vallfn = NULL;
+					continue;
+				}
 				t = longName + --lidx * 13;
 				for (k = 1; k < 11 && t < longName +
 				    sizeof(longName); k += 2) {