Re: [PATCH net-next v2 1/2] tcp: avoid false bind exhaustion with odd-sized port ranges

[Eric Dumazet]

Le mar. 10 nov. 2026 à 07:45, Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> a écrit :
>
> On Fri, 06 Nov 2026 19:14:41 +0200, Florin Badita-Nistor wrote:
> > inet_csk_find_open_port() rounds the range length down to an even
> > number but keeps the original exclusive upper bound for wrapping.
> > For an odd-sized range, the two scans can therefore miss a valid port
> > and return EADDRINUSE while an eligible port remains free.
> >
> > For example, restrict a TCP socket to IP_LOCAL_PORT_RANGE [40000, 40002]
> > and hold explicit binds on 40000 and 40001. bind(..., 0) always fails,
> > although an explicit bind to 40002 succeeds. Both IPv4 and IPv6 TCP and
>
> This is the reason of warning in set_local_port_range(),
> so kind of WAI to me.
>
> The change should be fine, but we should remove the warning.

I would keep the warning.

It was added in commit ed2dfd900992 ("tcp/dccp: warn user for preferred
ip_local_port_range") because connect() wants an even number of ports.
This is still the case: __inet_hash_connect() rounds an odd-sized netns
range down to an even size, so connect() can still miss one port there.

The per-socket IP_LOCAL_PORT_RANGE case has no warning at all, and
bind() can miss a free port there without any hint to the user.
This patch fixes that.

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>