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From f6f90d8f9f839a269226934cdba027b7af9bd900 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Tue, 24 Jun 2025 11:32:58 -0700
Subject: net: selftests: fix TCP packet checksum
From: Jakub Kicinski <kuba@kernel.org>
[ 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>
---
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 7af99d07762ea..946e92cca2111 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 {
--
2.39.5
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