ip_gre: add validation for csum_start

[ Upstream commit 1d011c4803c72f3907eccfc1ec63caefb852fcbf ]

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>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 9609ad71dd260a1162f6dd037010195c4f22f321..fe1801d9f05982eb28ccde2e1d228ef7845a355a 100644 (file)
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -353,6 +353,8 @@ 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);
 }