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

On Fri, 2016-02-12 at 13:25 +0000, Rainer Weikusat wrote:

Philipp Hahn [off-list ref] writes:

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Hello Rainer,

Am 11.02.2016 um 20:37 schrieb Rainer Weikusat:

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The unix_dgram_sendmsg routine use the following test

if (unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {

[...]

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

[...]

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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.