linux-kernel - Re: [PATCH net-next v02 1/2] af_packet: allow fanout

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Message-ID: <67068a44bff02_1cca3129431@willemb.c.googlers.com.notmuch>
Date: Wed, 09 Oct 2024 09:51:00 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Gur Stavi <gur.stavi@...wei.com>, 
 willemdebruijn.kernel@...il.com
Cc: davem@...emloft.net, 
 edumazet@...gle.com, 
 gur.stavi@...wei.com, 
 kuba@...nel.org, 
 linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, 
 netdev@...r.kernel.org, 
 pabeni@...hat.com, 
 shuah@...nel.org
Subject: Re: [PATCH net-next v02 1/2] af_packet: allow fanout_add when socket
 is not RUNNING

Gur Stavi wrote:
> >> @@ -1846,21 +1846,21 @@ static int fanout_add(struct sock *sk, struct fanout_args *args)
> >>  	err = -EINVAL;
> >>
> >>  	spin_lock(&po->bind_lock);
> >> -	if (packet_sock_flag(po, PACKET_SOCK_RUNNING) &&
> >> -	    match->type == type &&
> >> +	if (match->type == type &&
> >>  	    match->prot_hook.type == po->prot_hook.type &&
> >>  	    match->prot_hook.dev == po->prot_hook.dev) {
> >
> > Remaining unaddressed issue is that the socket can now be added
> > before being bound. See comment in v1.
> 
> I extended the psock_fanout test with unbound fanout test.
> 
> As far as I understand, the easiest way to verify bind is to test that
> po->prot_hook.dev != NULL, since we are under a bind_lock anyway.
> But perhaps a more readable and direct approach to test "bind" would be
> to test po->ifindex != -1, as ifindex is commented as "bound device".
> However, at the moment ifindex is not initialized to -1, I can add such
> initialization, but perhaps I do not fully understand all the logic.
> 
> Any preferences?

prot_hook.dev is not necessarily set if a packet socket is bound.
It may be bound to any device. See dev_add_pack and ptype_head.

prot_hook.type, on the other hand, must be set if bound and is only
modified with the bind_lock held too.

Well, and in packet_create. But setsockopt PACKET_FANOUT_ADD also
succeeds in case bind() was not called explicitly first to bind to
a specific device or change ptype.