netdev - Re: [PATCH net] af_unix: Guard against other == sk in unix_dgram

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Date:	Fri, 12 Feb 2016 13:25:15 +0000
From:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
To:	Philipp Hahn <pmhahn@...ahn.de>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, Karolin Seeger <kseeger@...ba.org>,
	Jason Baron <jbaron@...mai.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arvid Requate <requate@...vention.de>,
	Stefan Gohmann <gohmann@...vention.de>, netdev@...r.kernel.org
Subject: Re: [PATCH net] af_unix: Guard against other == sk in unix_dgram_sendmsg

Philipp Hahn <pmhahn@...ahn.de> writes:

> Hello Rainer,
>
> Am 11.02.2016 um 20:37 schrieb Rainer Weikusat:
>> The unix_dgram_sendmsg routine use the following test
>> 
>> if (unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {

[...]

>> This isn't correct as the> specified address could have been bound to
>> the sending socket itself

[...]

> After applying that patch at least my machine running the samba test no
> longer crashes.

There's a possible gotcha in there: Send-to-self used to be limited by
the queue limit. But the rationale for that (IIRC) was that someone
could keep using newly created sockets to queue ever more data to a
single, unrelated receiver. I don't think this should apply when
receiving and sending sockets are identical. But that's just my
opinion. The other option would be to avoid the unix_state_double_lock
for sk == other. I'd be willing to change this accordingly if someone
thinks the queue limit should apply to send-to-self.