[PATCH net-next] net: add missing check for TCP fraglist GRO

[Felix Fietkau <nbd@nbd.name>]

It turns out that the existing checks do not guarantee that the skb can be
pulled up to the GRO offset. When using the usb r8152 network driver with
GRO fraglist, the BUG() in __skb_pull is often triggered.
Fix the crash by adding the missing check.

Fixes: 8d95dc474f85 ("net: add code for TCP fraglist GRO")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 net/ipv4/tcp_offload.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index c90704befd7b..a71d2e623f0c 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -353,6 +353,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb,
 		flush |= (__force int)(flags ^ tcp_flag_word(th2));
 		flush |= skb->ip_summed != p->ip_summed;
 		flush |= skb->csum_level != p->csum_level;
+		flush |= !pskb_may_pull(skb, skb_gro_offset(skb));
 		flush |= NAPI_GRO_CB(p)->count >= 64;
 
 		if (flush || skb_gro_receive_list(p, skb))
-- 
2.44.0