[PATCH] gro: check returned skb of napi_frags_skb() against NULL

[Kaiyu Zhang <squirrel.prog@gmail.com>]

Some rogue network adapter and their driver pass bad skbs to GRO.
napi_frags_skb() detects this, drops these bad skbs, and return NULL
to napi_gro_frags(), which does not check returned skb against NULL
and access it. This results in a kernel crash.

A better approach to address these bad skbs would be to issue some
warnings and drop them, which napi_frags_skb() already does, and
move on without crashing the kernel.

Signed-off-by: Kaiyu Zhang <squirrel.prog@gmail.com>
---
 net/core/gro.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/gro.c b/net/core/gro.c
index 0759277dc..18d92016b 100644
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -731,6 +731,9 @@ gro_result_t napi_gro_frags(struct napi_struct *napi)
 	gro_result_t ret;
 	struct sk_buff *skb = napi_frags_skb(napi);
 
+	if (unlikely(!skb))
+		return GRO_CONSUMED;
+
 	trace_napi_gro_frags_entry(skb);
 
 	ret = napi_frags_finish(napi, skb, dev_gro_receive(napi, skb));
-- 
2.34.1