From 9f7fd60fb8f7138b33861fcdcd282fa62dd82472 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 [ Upstream commit 8d89661a36dd3bb8c9902cff36dc0c144dce3faf ] 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 Signed-off-by: Sasha Levin --- 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 29ca19ec82bb4..63938efd5b55f 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 { -- 2.47.3