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From:   Shreyansh Chouhan <chouhan.shreyansh630@gmail.com>
To:     davem@davemloft.net, yoshfuji@linux-ipv6.org, dsahern@kernel.org,
        kuba@kernel.org, pshelar@nicira.com,
        willemdebruijn.kernel@gmail.com
Cc:     Shreyansh Chouhan <chouhan.shreyansh630@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzbot+ff8e1b9f2f36481e2efc@syzkaller.appspotmail.com
Subject: [PATCH 1/2 net] ip_gre: add validation for csum_start
Date:   Sat, 21 Aug 2021 12:44:24 +0530
Message-Id: <20210821071425.512834-1-chouhan.shreyansh630@gmail.com>
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Validate csum_start in gre_handle_offloads before we call _gre_xmit so
that we do not crash later when the csum_start value is used in the
lco_csum function call.

This patch deals with ipv4 code.

Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
Reported-by: syzbot+ff8e1b9f2f36481e2efc@syzkaller.appspotmail.com
Signed-off-by: Shreyansh Chouhan <chouhan.shreyansh630@gmail.com>
---
 net/ipv4/ip_gre.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 12dca0c85f3c..95419b7adf5c 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -473,6 +473,8 @@ static void __gre_xmit(struct sk_buff *skb, struct net_device *dev,
 
 static int gre_handle_offloads(struct sk_buff *skb, bool csum)
 {
+	if (csum && skb_checksum_start(skb) < skb->data)
+		return -EINVAL;
 	return iptunnel_handle_offloads(skb, csum ? SKB_GSO_GRE_CSUM : SKB_GSO_GRE);
 }
 
-- 
2.31.1