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Sat, 12 Sep 2026 00:40:10 -0700 (PDT) Received: from 474444807712 named unknown by gmailapi.google.com with HTTPREST; Sat, 12 Sep 2026 07:40:09 +0000 Received: from 474444807712 named unknown by gmailapi.google.com with HTTPREST; Sat, 12 Sep 2026 07:40:09 +0000 From: Farhad Alemi X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Sat, 12 Sep 2026 07:40:09 +0000 X-Gm-Features: AcwNN1U7oiMPPggvAGkLxJ8f4FS-S3NfnynfUNKYcvJ3EJSPIXU-keM5UBnvdpg Message-ID: Subject: [PATCH net v2] net: remove WARN_ON_ONCE() from the dev_fill_forward_path() loop check To: David Ahern , Ido Schimmel , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: falemi@asu.edu, Simon Horman , Pablo Neira Ayuso , Florian Westphal , Lorenzo Bianconi , Xuanqiang Luo , netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 =3D=3D 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+0ovCgaRvbd0Udj70b2xxG8Cx3CaCpNhnf1V4= RWQuDveZYZhA@mail.gmail.com/ Suggested-by: Pablo Neira Ayuso Assisted-by: Claude:claude-opus-5 syzkaller Signed-off-by: Farhad Alemi Reviewed-by: Xuanqiang Luo --- v2: - Remove the WARN_ON_ONCE() in dev_fill_forward_path() instead of rejecting the looping route in the tunnel drivers (Pablo Neira Ayuso). - Add the Fixes: tags (Xuanqiang Luo). v1: https://lore.kernel.org/all/CA+0ovCj+Pd5owGH+51rA8-RDu9YFx5oYUv8bV0zOE7= 2QgVfY0A@mail.gmail.com/ diff --git a/net/core/dev.c b/net/core/dev.c index ecfbd72d5d1a..c67900354fa6 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 goto err_out; stack->num_paths++; - if (WARN_ON_ONCE(last_dev =3D=3D ctx->dev)) + if (last_dev =3D=3D ctx->dev) goto err_out; } --=20 2.53.0