netdev - [PATCH 2/2] xfrm: set ipv4 no_pmtu_disc flag only on output sa when direction is set

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Message-ID: <20260114121817.1106134-3-steffen.klassert@secunet.com>
Date: Wed, 14 Jan 2026 13:18:09 +0100
From: Steffen Klassert <steffen.klassert@...unet.com>
To: David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>
CC: Herbert Xu <herbert@...dor.apana.org.au>, Steffen Klassert
	<steffen.klassert@...unet.com>, <netdev@...r.kernel.org>
Subject: [PATCH 2/2] xfrm: set ipv4 no_pmtu_disc flag only on output sa when direction is set

From: Antony Antony <antony.antony@...unet.com>

The XFRM_STATE_NOPMTUDISC flag is only meaningful for output SAs, but
it was being applied regardless of the SA direction when the sysctl
ip_no_pmtu_disc is enabled. This can unintentionally affect input SAs.

Limit setting XFRM_STATE_NOPMTUDISC to output SAs when the SA direction
is configured.

Closes: https://github.com/strongswan/strongswan/issues/2946
Fixes: a4a87fa4e96c ("xfrm: Add Direction to the SA in or out")
Signed-off-by: Antony Antony <antony.antony@...unet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
---
 net/xfrm/xfrm_state.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 9e14e453b55c..98b362d51836 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -3151,6 +3151,7 @@ int __xfrm_init_state(struct xfrm_state *x, struct netlink_ext_ack *extack)
 	int err;
 
 	if (family == AF_INET &&
+	    (!x->dir || x->dir == XFRM_SA_DIR_OUT) &&
 	    READ_ONCE(xs_net(x)->ipv4.sysctl_ip_no_pmtu_disc))
 		x->props.flags |= XFRM_STATE_NOPMTUDISC;
 
-- 
2.43.0