linux-kernel - [PATCH net-next v4 1/2] icmp: fix ICMP error source address when xfrm policy matches

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Message-ID: <f820e0e9f80b1467f97d1408f00f61b1fdb1b986.1769595011.git.antony.antony@secunet.com>
Date: Wed, 28 Jan 2026 11:25:14 +0100
From: Antony Antony <antony.antony@...unet.com>
To: Antony Antony <antony.antony@...unet.com>, Jakub Kicinski
	<kuba@...nel.org>, Steffen Klassert <steffen.klassert@...unet.com>,
	<netdev@...r.kernel.org>
CC: "David S . Miller" <davem@...emloft.net>, David Ahern
	<dsahern@...nel.org>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
	<pabeni@...hat.com>, Herbert Xu <herbert@...dor.apana.org.au>, Shuah Khan
	<shuah@...nel.org>, <devel@...ux-ipsec.org>, Tobias Brunner
	<tobias@...ongswan.org>, Simon Horman <horms@...nel.org>,
	<stable+noautosel@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH net-next v4 1/2] icmp: fix ICMP error source address when xfrm policy matches

When an IPsec gateway generates an ICMP error (e.g., Destination Host
Unreachable), the source address incorrectly shows the unreachable
destination instead of the gateway's address. IPv6 behaves correctly.

Before fix:
  ping 10.1.6.3
  From 10.1.6.3 icmp_seq=1 Destination Host Unreachable
  (wrong - 10.1.6.3 is the unreachable host)

After fix:
  ping 10.1.6.3
  From 10.1.5.2 icmp_seq=1 Destination Host Unreachable
  (correct - 10.1.5.2 is the gateway)

The fix removes the memcpy that overwrote fl4 with fl4_dec after
xfrm_lookup(). A follow-up commit adds a selftest.

Fixes: 415b3334a21a ("icmp: Fix regression in nexthop resolution during replies.")
Cc: stable+noautosel@...nel.org # Avoid false positives in tests
Signed-off-by: Antony Antony <antony.antony@...unet.com>
Acked-by: Tobias Brunner <tobias@...ongswan.org>
---
 net/ipv4/icmp.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 19c9c838967f..4bd421208ce0 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -569,7 +569,6 @@ static struct rtable *icmp_route_lookup(struct net *net, struct flowi4 *fl4,
 	rt2 = dst_rtable(dst2);
 	if (!IS_ERR(dst2)) {
 		dst_release(&rt->dst);
-		memcpy(fl4, &fl4_dec, sizeof(*fl4));
 		rt = rt2;
 	} else if (PTR_ERR(dst2) == -EPERM) {
 		if (rt)
--
2.39.5