Re: [REGRESSION] 5.15.88 and onwards no longer return EADDRINUSE from bind

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Greg KH <gregkh@linuxfoundation.org>
Date:   Mon, 13 Feb 2023 18:48:48 +0100
> On Mon, Feb 13, 2023 at 08:44:55AM -0800, Kuniyuki Iwashima wrote:
> > From:   Willy Tarreau <w@1wt.eu>
> > Date:   Mon, 13 Feb 2023 08:52:34 +0100
> > > Hi Greg,
> > > 
> > > On Mon, Feb 13, 2023 at 08:25:34AM +0100, Greg KH wrote:
> > > > On Mon, Feb 13, 2023 at 05:27:03AM +0100, Willy Tarreau wrote:
> > > > > Hi,
> > > > > 
> > > > > [CCed netdev]
> > > > > 
> > > > > On Sun, Feb 12, 2023 at 10:38:40PM -0500, Winter wrote:
> > > > > > Hi all,
> > > > > > 
> > > > > > I'm facing the same issue as
> > > > > > https://lore.kernel.org/stable/CAFsF8vL4CGFzWMb38_XviiEgxoKX0GYup=JiUFXUOmagdk9CRg@mail.gmail.com/,
> > > > > > but on 5.15. I've bisected it across releases to 5.15.88, and can reproduce
> > > > > > on 5.15.93.
> > > > > > 
> > > > > > However, I cannot seem to find the identified problematic commit in the 5.15
> > > > > > branch, so I'm unsure if this is a different issue or not.
> > > > > > 
> > > > > > There's a few ways to reproduce this issue, but the one I've been using is
> > > > > > running libuv's (https://github.com/libuv/libuv) tests, specifically tests
> > > > > > 271 and 277.
> > > > > 
> > > > > >From the linked patch:
> > > > > 
> > > > >   https://lore.kernel.org/stable/20221228144337.512799851@linuxfoundation.org/
> > > > 
> > > > But that commit only ended up in 6.0.y, not 5.15, so how is this an
> > > > issue in 5.15.y?
> > > 
> > > Hmmm I plead -ENOCOFFEE on my side, I hadn't notice the "can't find the
> > > problematic commit", you're right indeed.
> > > 
> > > However if the issue happened in 5.15.88, the only part touching the
> > > network listening area is this one which may introduce an EINVAL on
> > > one listening path, but that seems unrelated to me given that it's
> > > only for ULP that libuv doesn't seem to be using:
> > > 
> > >   dadd0dcaa67d ("net/ulp: prevent ULP without clone op from entering the LISTEN status")
> > 
> > This commit accidentally backports a part of 7a7160edf1bf ("net: Return
> > errno in sk->sk_prot->get_port().") and removed err = -EADDRINUSE in
> > inet_csk_listen_start().  Then, listen() will return 0 even if ->get_port()
> > actually fails and returns 1.
> > 
> > I can send a small revert or a whole backport, but which is preferable ?
> > The original patch is not for stable, but it will make future backports
> > easy.
> 
> A whole revert is probably best, if it's not needed.  But if it is, a
> fix up would be fine to get as well.

dadd0dcaa67d is needed to fix potential double-free, so could you queue
this fixup for 5.15. ?

---8<---
From ad319ace8b5c1dd5105b7263b7ccfd0ba0926551 Mon Sep 17 00:00:00 2001
From: Kuniyuki Iwashima <kuniyu@amazon.com>
Date: Mon, 13 Feb 2023 20:45:48 +0000
Subject: [PATCH] tcp: Fix listen() regression in 5.15.88.

When we backport dadd0dcaa67d ("net/ulp: prevent ULP without clone op from
entering the LISTEN status"), we have accidentally backported a part of
7a7160edf1bf ("net: Return errno in sk->sk_prot->get_port().") and removed
err = -EADDRINUSE in inet_csk_listen_start().

Thus, listen() no longer returns -EADDRINUSE even if ->get_port() failed
as reported in [0].

We set -EADDRINUSE to err just before ->get_port() to fix the regression.

[0]: https://lore.kernel.org/stable/EF8A45D0-768A-4CD5-9A8A-0FA6E610ABF7@winter.cafe/

Reported-by: Winter <winter@winter.cafe>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 net/ipv4/inet_connection_sock.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index a86140ff093c..29ec42c1f5d0 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -1070,6 +1070,7 @@ int inet_csk_listen_start(struct sock *sk, int backlog)
 	 * It is OK, because this socket enters to hash table only
 	 * after validation is complete.
 	 */
+	err = -EADDRINUSE;
 	inet_sk_state_store(sk, TCP_LISTEN);
 	if (!sk->sk_prot->get_port(sk, inet->inet_num)) {
 		inet->inet_sport = htons(inet->inet_num);
-- 
2.38.1
---8<---

Thanks,
Kuniyuki