5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Antonio Pastor antonio.pastor@gmail.com
[ Upstream commit a024e377efed31ecfb39210bed562932321345b3 ]
802.2+LLC+SNAP frames received by napi_complete_done with GRO and DSA have skb->transport_header set two bytes short, or pointing 2 bytes before network_header & skb->data. As snap_rcv expects transport_header to point to SNAP header (OID:PID) after LLC processing advances offset over LLC header (llc_rcv & llc_fixup_skb), code doesn't find a match and packet is dropped.
Between napi_complete_done and snap_rcv, transport_header is not used until __netif_receive_skb_core, where originally it was being reset. Commit fda55eca5a33 ("net: introduce skb_transport_header_was_set()") only does so if not set, on the assumption the value was set correctly by GRO (and also on assumption that "network stacks usually reset the transport header anyway"). Afterwards it is moved forward by llc_fixup_skb.
Locally generated traffic shows up at __netif_receive_skb_core with no transport_header set and is processed without issue. On a setup with GRO but no DSA, transport_header and network_header are both set to point to skb->data which is also correct.
As issue is LLC specific, to avoid impacting non-LLC traffic, and to follow up on original assumption made on previous code change, llc_fixup_skb to reset the offset after skb pull. llc_fixup_skb assumes the LLC header is at skb->data, and by definition SNAP header immediately follows.
Fixes: fda55eca5a33 ("net: introduce skb_transport_header_was_set()") Signed-off-by: Antonio Pastor antonio.pastor@gmail.com Reviewed-by: Eric Dumazet edumazet@google.com Link: https://patch.msgid.link/20241225010723.2830290-1-antonio.pastor@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/llc/llc_input.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/llc/llc_input.c b/net/llc/llc_input.c index f4fb309185ce..4229c349651d 100644 --- a/net/llc/llc_input.c +++ b/net/llc/llc_input.c @@ -124,8 +124,8 @@ static inline int llc_fixup_skb(struct sk_buff *skb) if (unlikely(!pskb_may_pull(skb, llc_len))) return 0;
- skb->transport_header += llc_len; skb_pull(skb, llc_len); + skb_reset_transport_header(skb); if (skb->protocol == htons(ETH_P_802_2)) { __be16 pdulen; s32 data_size;