netdev - [PATCH net] xfrm: Clear low order bits of ->flowi4_tos in decode

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Date: Wed, 3 Jan 2024 16:06:32 +0100
From: Guillaume Nault <gnault@...hat.com>
To: David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, Florian Westphal <fw@...len.de>,
	Simon Horman <horms@...nel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Steffen Klassert <steffen.klassert@...unet.com>
Subject: [PATCH net] xfrm: Clear low order bits of ->flowi4_tos in
 decode_session4().

Commit 23e7b1bfed61 ("xfrm: Don't accidentally set RTO_ONLINK in
decode_session4()") fixed a problem where decode_session4() could
erroneously set the RTO_ONLINK flag for IPv4 route lookups. This
problem was reintroduced when decode_session4() was modified to
use the flow dissector.

Fix this by clearing again the two low order bits of ->flowi4_tos.
Found by code inspection, compile tested only.

Fixes: 7a0207094f1b ("xfrm: policy: replace session decode with flow dissector")
Signed-off-by: Guillaume Nault <gnault@...hat.com>
---
 net/xfrm/xfrm_policy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index c13dc3ef7910..e69d588caa0c 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -3416,7 +3416,7 @@ decode_session4(const struct xfrm_flow_keys *flkeys, struct flowi *fl, bool reve
 	}
 
 	fl4->flowi4_proto = flkeys->basic.ip_proto;
-	fl4->flowi4_tos = flkeys->ip.tos;
+	fl4->flowi4_tos = flkeys->ip.tos & ~INET_ECN_MASK;
 }
 
 #if IS_ENABLED(CONFIG_IPV6)
-- 
2.39.2