Re: [PATCH v1 net] tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Jakub Kicinski <kuba@kernel.org>
Date: Mon, 7 Oct 2024 16:26:10 -0700
> On Mon, 7 Oct 2024 07:15:57 -0700 Kuniyuki Iwashima wrote:
> > Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler().
> > 
> >   """
> >   We are seeing a use-after-free from a bpf prog attached to
> >   trace_tcp_retransmit_synack. The program passes the req->sk to the
> >   bpf_sk_storage_get_tracing kernel helper which does check for null
> >   before using it.
> >   """
> 
> I think this crashes a bunch of selftests, example:
> 
> https://netdev-3.bots.linux.dev/vmksft-nf-dbg/results/805581/8-nft-queue-sh/stderr

Oops, sorry, I copy-and-pasted __inet_csk_reqsk_queue_drop()
for different reqsk.  I'll squash the diff below.

---8<---
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 36f03d51356e..433c80dc57d5 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -1188,7 +1190,7 @@ static void reqsk_timer_handler(struct timer_list *t)
 	}
 
 drop:
-	__inet_csk_reqsk_queue_drop(sk_listener, nreq, true);
+	__inet_csk_reqsk_queue_drop(sk_listener, oreq, true);
 	reqsk_put(req);
 }
 
---8<---

Thanks!