From 0804d77fd6e67426328ad94b2fed6b4afee6dc18 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 7af99d07762e..946e92cca211 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 {