From 7f2b7ec93c347ef81cb6048c6895b967feaa2260 Mon Sep 17 00:00:00 2001
From: Xin LI <delphij@FreeBSD.org>
Date: Fri, 13 Jul 2018 02:02:16 +0000
Subject: [PATCH] Detect and handle invalid number of FATs

If the number of FATs field in the boot sector is zero, give
an appropriate error code.

Obtained from:	Android https://android.googlesource.com/platform/external/fsck_msdos/+/6c29bbe8d58e6fe8755935a04166ecf82ff31f47%5E%21/
MFC after:	2 weeks
---
 sbin/fsck_msdosfs/boot.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sbin/fsck_msdosfs/boot.c b/sbin/fsck_msdosfs/boot.c
index 9a954d07ae9..9e0958a9454 100644
--- a/sbin/fsck_msdosfs/boot.c
+++ b/sbin/fsck_msdosfs/boot.c
@@ -87,6 +87,10 @@ readboot(int dosfs, struct bootblock *boot)
 		pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
 		return FSFATAL;
 	}
+	if (boot->bpbFATs == 0) {
+		pfatal("Invalid number of FATs: %u", boot->bpbFATs);
+		return FSFATAL;
+	}
 	if (!boot->bpbRootDirEnts)
 		boot->flags |= FAT32;
 	if (boot->flags & FAT32) {