Re: [PATCH v3 net 2/2] tcp: use the echoed source route in cookie_v4_check()
flat view
From: Kuniyuki Iwashima <kuniyu@google.com>
Date: 2026-10-13 01:25:36
On Mon, Oct 12, 2026 at 3:10 AM Eric Dumazet [off-list ref] wrote:
When the ACK carries a source route option, cookie_v4_check() routes
the new socket to opt->faddr, where opt points to the options of the
received packet.
ip_options_compile() only fills faddr for options given by
setsockopt() (when called without an skb), so on receive faddr is 0
and the lookup is done for daddr 0, which gives a local route.
Use the options echoed by tcp_v4_save_options() instead, as
inet_csk_route_req() and inet_csk_route_child_sock() do with
ireq->ireq_opt. Read them after security_inet_conn_request(),
since CIPSO can replace ireq->ireq_opt there.
The route now goes to the first hop of the source route, so also
refuse a strict source route through a gateway, as
inet_csk_route_req() does.
Found by sashiko while reviewing the sk_mc_loop() fix.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@kernel.org>Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>