netdev - [PATCH net-next] net: avoid skb_warn_bad_offload on IS

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Date:   Tue, 12 Dec 2017 11:39:04 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     netdev@...r.kernel.org
Cc:     edumazet@...gle.com, davem@...emloft.net,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net-next] net: avoid skb_warn_bad_offload on IS_ERR

From: Willem de Bruijn <willemb@...gle.com>

skb_warn_bad_offload warns when packets enter the GSO stack that
require skb_checksum_help or vice versa. Do not warn on arbitrary
bad packets. Packet sockets can craft many. Syzkaller was able to
demonstrate another one with eth_type games.

In particular, suppress the warning when segmentation returns an
error, which is for reasons other than checksum offload.

See also commit 36c92474498a ("net: WARN if skb_checksum_help() is
called on skb requiring segmentation") for context on this warning.

Signed-off-by: Willem de Bruijn <willemb@...gle.com>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 8aa2f70995e8..b0eee49a2489 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2803,7 +2803,7 @@ struct sk_buff *__skb_gso_segment(struct sk_buff *skb,

 	segs = skb_mac_gso_segment(skb, features);

-	if (unlikely(skb_needs_check(skb, tx_path)))
+	if (unlikely(skb_needs_check(skb, tx_path) && !IS_ERR(segs)))
 		skb_warn_bad_offload(skb);

 	return segs;
-- 
2.15.1.424.g9478a66081-goog