linux-kernel - [PATCH] seg6: Fix slab-out-of-bounds in fl6_update

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Date:   Tue, 2 Jun 2020 14:51:55 +0800
From:   YueHaibing <yuehaibing@...wei.com>
To:     <davem@...emloft.net>, <kuznet@....inr.ac.ru>,
        <yoshfuji@...ux-ipv6.org>, <kuba@...nel.org>,
        <alex.aring@...il.com>, <ahabdels@...il.com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        YueHaibing <yuehaibing@...wei.com>
Subject: [PATCH] seg6: Fix slab-out-of-bounds in fl6_update_dst()

When update flowi6 daddr in fl6_update_dst() for srcrt, the used index
of segments should be segments_left minus one per RFC8754
(section 4.3.1.1) S15 S16. Otherwise it may results in an out-of-bounds
read.

Reported-by: syzbot+e8c028b62439eac42073@...kaller.appspotmail.com
Fixes: 0cb7498f234e ("seg6: fix SRH processing to comply with RFC8754")
Signed-off-by: YueHaibing <yuehaibing@...wei.com>
---
 net/ipv6/exthdrs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 5a8bbcdcaf2b..f5304bf33ab1 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -1353,7 +1353,7 @@ struct in6_addr *fl6_update_dst(struct flowi6 *fl6,
 	{
 		struct ipv6_sr_hdr *srh = (struct ipv6_sr_hdr *)opt->srcrt;
 
-		fl6->daddr = srh->segments[srh->segments_left];
+		fl6->daddr = srh->segments[srh->segments_left - 1];
 		break;
 	}
 	default:
-- 
2.17.1