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 <kuba@kernel.org>
Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Reported-by: Oleksij Rempel <o.rempel@pengutronix.de>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20250624183258.3377740-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/core/selftests.c b/net/core/selftests.c
index 7af99d07762ea0e50cafcacb180104aa370856a8..946e92cca2111057c817ffd7f49eadb976c9a60f 100644 (file)
--- 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 {