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From:   Phillip Potter <phil@philpotter.co.uk>
To:     davem@davemloft.net
Cc:     kuba@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, edumazet@google.com
Subject: [PATCH] net: geneve: check skb is large enough for IPv4/IPv6 header
Date:   Sun, 11 Apr 2021 12:28:24 +0100
Message-Id: <20210411112824.1149-1-phil@philpotter.co.uk>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Check within geneve_xmit_skb/geneve6_xmit_skb that sk_buff structure
is large enough to include IPv4 or IPv6 header, and reject if not. The
geneve_xmit_skb portion and overall idea was contributed by Eric Dumazet.
Fixes a KMSAN-found uninit-value bug reported by syzbot at:
https://syzkaller.appspot.com/bug?id=abe95dc3e3e9667fc23b8d81f29ecad95c6f106f

Suggested-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot+2e406a9ac75bb71d4b7a@syzkaller.appspotmail.com
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
---
 drivers/net/geneve.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 5523f069b9a5..adfceb60f7f8 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -891,6 +891,9 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	__be16 sport;
 	int err;
 
+	if (!pskb_network_may_pull(skb, sizeof(struct iphdr)))
+		return -EINVAL;
+
 	sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true);
 	rt = geneve_get_v4_rt(skb, dev, gs4, &fl4, info,
 			      geneve->cfg.info.key.tp_dst, sport);
@@ -977,6 +980,9 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	__be16 sport;
 	int err;
 
+	if (!pskb_network_may_pull(skb, sizeof(struct ipv6hdr)))
+		return -EINVAL;
+
 	sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true);
 	dst = geneve_get_v6_dst(skb, dev, gs6, &fl6, info,
 				geneve->cfg.info.key.tp_dst, sport);
-- 
2.30.2