From: Jason Baron <jbaron@akamai.com>
To: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Cc: davem@davemloft.net, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, minipli@googlemail.com,
normalperson@yhbt.net, eric.dumazet@gmail.com,
viro@zeniv.linux.org.uk, davidel@xmailserver.org,
dave@stgolabs.net, olivier@mauras.ch, pageexec@freemail.hu,
torvalds@linux-foundation.org, peterz@infradead.org
Subject: Re: [PATCH v2 1/3] unix: fix use-after-free in unix_dgram_poll()
Date: Mon, 19 Oct 2015 11:07:40 -0400 [thread overview]
Message-ID: <5625073C.5010809@akamai.com> (raw)
In-Reply-To: <87fv17x59w.fsf@doppelsaurus.mobileactivedefense.com>
On 10/18/2015 04:58 PM, Rainer Weikusat wrote:
[...]
>
> The idea behind 'the wait queue' (insofar I'm aware of it) is that it
> will be used as list of threads who need to be notified when the
> associated event occurs. Since you seem to argue that the run-of-the-mill
> algorithm is too slow for this particular case, is there anything to
> back this up?
>
Generally the poll() routines only add to a wait queue once at the
beginning, and all subsequent calls to poll() simply check the wakeup
conditions. So here you are proposing to add/remove to the wait queue on
subsequent invocations of poll(). So the initial patch I did, continued
in the usual pattern and only added once on registration or connect().
However, I do think that this is a special case since the registration
is on a shared wait queue, and thus having a long list of registered
waiters is going to affect all waiters. So I am fine with doing the
add/removes in the poll() routine and I agree that the patch below is
more compact that what I initially posted.
A couple of notes on your patch:
1)
In unix_peer_wake_relay() function, 'sk_wq' is an __rcu pointer and thus
it requires proper dereferencing. Something like:
struct unix_sock *u;
struct socket_wq *wq;
u = container_of(wait, struct unix_sock, wait);
rcu_read_lock();
wq = rcu_dereference(u->sk.sk_wq);
if (wq_has_sleeper(wq))
wake_up_interruptible_sync_poll(&wq->wait, key);
rcu_read_unlock();
2)
For the case of epoll() in edge triggered mode we need to ensure that
when we return -EAGAIN from unix_dgram_sendmsg() when unix_recvq_full()
is true, we need to add a unix_peer_wake_connect() call to guarantee a
wakeup. Otherwise, we are going to potentially hang there.
With these changes (or tell me why they are not needed), I'm happy to
ack this patch.
Thanks,
-Jason
next prev parent reply other threads:[~2015-10-19 15:07 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-02 20:43 [PATCH v2 0/3] af_unix: fix use-after-free Jason Baron
2015-10-02 20:43 ` [PATCH v2 1/3] unix: fix use-after-free in unix_dgram_poll() Jason Baron
2015-10-03 5:46 ` Mathias Krause
2015-10-03 17:02 ` Rainer Weikusat
2015-10-04 17:41 ` Rainer Weikusat
2015-10-05 16:31 ` Rainer Weikusat
2015-10-05 16:54 ` Eric Dumazet
2015-10-05 17:20 ` Rainer Weikusat
2015-10-05 17:55 ` Jason Baron
2015-10-12 20:41 ` Rainer Weikusat
2015-10-14 3:44 ` Jason Baron
2015-10-14 17:47 ` Rainer Weikusat
2015-10-15 2:54 ` Jason Baron
2015-10-18 20:58 ` Rainer Weikusat
2015-10-19 15:07 ` Jason Baron [this message]
2015-10-20 22:29 ` Rainer Weikusat
2015-10-21 17:34 ` Rainer Weikusat
2015-10-28 16:46 ` [RFC] " Rainer Weikusat
2015-10-28 17:57 ` Jason Baron
2015-10-29 14:23 ` Rainer Weikusat
2015-10-30 20:52 ` [RFC] unix: fix use-after-free in unix_dgram_poll()/ 4.2.5 Rainer Weikusat
[not found] ` <57d2f5b6aae251957bff7a1a52b8bf2c@core-hosting.net>
2015-11-02 21:55 ` Rainer Weikusat
2015-10-02 20:43 ` [PATCH v2 2/3] af_unix: Convert gc_flags to flags Jason Baron
2015-10-02 20:44 ` [PATCH v2 3/3] af_unix: optimize the unix_dgram_recvmsg() Jason Baron
2015-10-05 7:41 ` Peter Zijlstra
2015-10-05 17:13 ` Jason Baron
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