From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Pablo Neira Ayuso <pablo@netfilter.org>,
	Farhad Alemi <farhad.alemi@berkeley.edu>,
	Xuanqiang Luo <luoxuanqiang@kylinos.cn>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 7.2 209/438] net: remove WARN_ON_ONCE() from the dev_fill_forward_path() loop check
Date: Wed, 23 Sep 2026 16:03:50 +0200
Message-ID: <20260923140650.177967426@linuxfoundation.org>
In-Reply-To: <20260923140644.756254324@linuxfoundation.org>
References: <20260923140644.756254324@linuxfoundation.org>
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7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Farhad Alemi <farhad.alemi@berkeley.edu>

[ Upstream commit 150dba2c69e93302af24a0c868eebe4871e2e107 ]

ipip_fill_forward_path() and ip6_tnl_fill_forward_path() look up the
route to the tunnel's remote endpoint and set ctx->dev to its device,
which is the tunnel itself when that route resolves back to the tunnel.
dev_fill_forward_path() then makes no progress and trips
WARN_ON_ONCE(last_dev == ctx->dev) as soon as a flowtable tries to
offload a flow through the tunnel. That routing loop is a configuration
any CAP_NET_ADMIN user can set up, and ip_tunnel_xmit() and
ip6_tnl_xmit() already treat it as a tx error, so remove the warning and
just fail the walk, as commit 008e7a7c293b ("net: remove WARN_ON_ONCE
when accessing forward path array") did for the path stack overflow.

Fixes: ab427db17885 ("netfilter: flowtable: Add IPIP rx sw acceleration")
Fixes: d98103575dcd ("netfilter: flowtable: Add IP6IP6 rx sw acceleration")
Closes: https://lore.kernel.org/all/CA+0ovCgaRvbd0Udj70b2xxG8Cx3CaCpNhnf1V4RWQuDveZYZhA@mail.gmail.com/
Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Reviewed-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>
Link: https://patch.msgid.link/CA+0ovCgKDOk+Bg6Gh5Lwx94u_jJjQ30-vY1JcY2BYfhnWJJbPA@mail.gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 679e75d3699ae..ff25e4c71588e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -789,7 +789,7 @@ int dev_fill_forward_path(struct net_device_path_ctx *ctx,
 			goto err_out;
 
 		stack->num_paths++;
-		if (WARN_ON_ONCE(last_dev == ctx->dev))
+		if (last_dev == ctx->dev)
 			goto err_out;
 	}
 
-- 
2.53.0