From: Farhad Alemi 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 Assisted-by: Claude:claude-opus-5 syzkaller Signed-off-by: Farhad Alemi Signed-off-by: Pablo Neira Ayuso --- 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 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 *ctx, goto err_out; stack->num_paths++; - if (WARN_ON_ONCE(last_dev == ctx->dev)) + if (last_dev == ctx->dev) goto err_out; } -- 2.47.3