The skb_gro_receive_list() function is missing a critical safety check that exists in the skb_gro_receive() implementation. Specifically, it does not validate NAPI_GRO_CB(skb)->flush before allowing packet aggregation This allows already-GRO'd packets with existing frag_list to be re-aggregated into a new GRO session, corrupting the frag_list chain structure. When skb_segment() attempts to unpack these malformed packets, it encounters invalid state and triggers a kernel panic. Scenario (Tethering/Device forwarding): 1. Driver: Generated aggregated packet P1 via LRO with frag_list 2. Dev A: Receives aggregated fraglist packet and flush flag set 3. Dev A: Re-enters GRO, skb_gro_receive_list() is called 4. Missing flush check allows re-aggregation despite flush flag 5. Frag_list chain becomes corrupted (loops or dangling refs) 6. Dev B: TX path calls skb_segment(), crashes on corrupted frag_list Root cause in skb_segment(): The check at line ~4891: if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) && (skb_headlen(list_skb) == len || sg)) { When frag_list is corrupted by double aggregation, when list_skb is a NULL pointer from skb->next, skb_headlen(list_skb) dereference NULL/corrupted pointers occurs. Call Trace: skb_headlen(NULL skb) skb_segment tcp_gso_segment tcp4_gso_segment inet_gso_segment skb_mac_gso_segment __skb_gso_segment skb_gso_segment validate_xmit_skb validate_xmit_skb_list sch_direct_xmit qdisc_restart __qdisc_run qdisc_run net_tx_action Fix: Add NAPI_GRO_CB(skb)->flush validation to the early-return check in skb_gro_receive_list(), matching the defensive programming pattern of skb_gro_receive(). Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.") Cc: stable@vger.kernel.org Signed-off-by: Shiming Cheng --- net/core/gro.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/net/core/gro.c b/net/core/gro.c index 35f2f708f010..b1573d98f3a5 100644 --- a/net/core/gro.c +++ b/net/core/gro.c @@ -229,7 +229,14 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) int skb_gro_receive_list(struct sk_buff *p, struct sk_buff *skb) { - if (unlikely(p->len + skb->len >= 65536)) + /* + * Packets marked with NAPI_GRO_CB(skb)->flush have already gone + * through GRO/LRO processing and must not be aggregated again. + * Re-entering frag_list GRO may corrupt the frag_list chain and + * later crash during GSO segmentaiont. + */ + if (unlikely(p->len + skb->len >= 65536 || + NAPI_GRO_CB(skb)->flush)) return -E2BIG; if (!pskb_may_pull(skb, skb_gro_offset(skb))) { -- 2.45.2