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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Muhammad Usama Anjum <musamaanjum@gmail.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.11 015/210] net: ipv6: check for validity before dereferencing cfg->fc_nlinfo.nlh
Date:   Mon, 12 Apr 2021 10:38:40 +0200
Message-Id: <20210412084016.513159862@linuxfoundation.org>
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From: Muhammad Usama Anjum <musamaanjum@gmail.com>

commit 864db232dc7036aa2de19749c3d5be0143b24f8f upstream.

nlh is being checked for validtity two times when it is dereferenced in
this function. Check for validity again when updating the flags through
nlh pointer to make the dereferencing safe.

CC: <stable@vger.kernel.org>
Addresses-Coverity: ("NULL pointer dereference")
Signed-off-by: Muhammad Usama Anjum <musamaanjum@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/route.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -5203,9 +5203,11 @@ static int ip6_route_multipath_add(struc
 		 * nexthops have been replaced by first new, the rest should
 		 * be added to it.
 		 */
-		cfg->fc_nlinfo.nlh->nlmsg_flags &= ~(NLM_F_EXCL |
-						     NLM_F_REPLACE);
-		cfg->fc_nlinfo.nlh->nlmsg_flags |= NLM_F_CREATE;
+		if (cfg->fc_nlinfo.nlh) {
+			cfg->fc_nlinfo.nlh->nlmsg_flags &= ~(NLM_F_EXCL |
+							     NLM_F_REPLACE);
+			cfg->fc_nlinfo.nlh->nlmsg_flags |= NLM_F_CREATE;
+		}
 		nhn++;
 	}