[PATCH net] net: gro: set the last skb->next to NULL when it get merged

[kerneljasonxing@gmail.com]

From: Jason Xing <xingwanli@kuaishou.com>

Setting the @next of the last skb to NULL to prevent the panic in future
when someone does something to the last of the gro list but its @next is
invalid.

For example, without the fix (commit: ece23711dd95), a panic could happen
with the clsact loaded when skb is redirected and then validated in
validate_xmit_skb_list() which could access the error addr of the @next
of the last skb. Thus, "general protection fault" would appear after that.

Signed-off-by: Jason Xing <xingwanli@kuaishou.com>
---
 net/core/skbuff.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 2170bea..7b248f1 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4396,6 +4396,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
 		skb_shinfo(p)->frag_list = skb;
 	else
 		NAPI_GRO_CB(p)->last->next = skb;
+	skb->next = NULL;
 	NAPI_GRO_CB(p)->last = skb;
 	__skb_header_release(skb);
 	lp = p;
-- 
1.8.3.1