Re: [PATCH net] af_unix: Guard against other == sk in unix_dgram_sendmsg

[Ben Hutchings]

On Fri, 2016-02-12 at 13:25 +0000, Rainer Weikusat wrote:
> Philipp Hahn <pmhahn@xxxxxxxxx> 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.

Given that unix_state_double_lock() already handles sk == other, I'm
not sure why you think it needs to be avoided.

> I'd be willing to change this accordingly if someone
> thinks the queue limit should apply to send-to-self.

If we don't check the queue limit here, does anything else prevent the
queue growing to the point it's a DoS?

Ben.

-- 
Ben Hutchings
I say we take off; nuke the site from orbit.  It's the only way to be sure.

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