From 8d89661a36dd3bb8c9902cff36dc0c144dce3faf Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Tue, 24 Jun 2025 11:32:58 -0700 Subject: [PATCH] net: selftests: fix TCP packet checksum The length in the pseudo header should be the length of the L3 payload AKA the L4 header+payload. The selftest code builds the packet from the lower layers up, so all the headers are pushed already when it constructs L4. We need to subtract the lower layer headers from skb->len. Fixes: 3e1e58d64c3d ("net: add generic selftest support") Signed-off-by: Jakub Kicinski Reviewed-by: Gerhard Engleder Reported-by: Oleksij Rempel Tested-by: Oleksij Rempel Reviewed-by: Oleksij Rempel Link: https://patch.msgid.link/20250624183258.3377740-1-kuba@kernel.org Signed-off-by: Paolo Abeni --- net/core/selftests.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/core/selftests.c b/net/core/selftests.c index 35f807ea9952..406faf8e5f3f 100644 --- a/net/core/selftests.c +++ b/net/core/selftests.c @@ -160,8 +160,9 @@ static struct sk_buff *net_test_get_skb(struct net_device *ndev, skb->csum = 0; skb->ip_summed = CHECKSUM_PARTIAL; if (attr->tcp) { - thdr->check = ~tcp_v4_check(skb->len, ihdr->saddr, - ihdr->daddr, 0); + int l4len = skb->len - skb_transport_offset(skb); + + thdr->check = ~tcp_v4_check(l4len, ihdr->saddr, ihdr->daddr, 0); skb->csum_start = skb_transport_header(skb) - skb->head; skb->csum_offset = offsetof(struct tcphdr, check); } else { -- 2.25.1