Re: use-after-free in sock_wake_async

[Eric Dumazet]

On Wed, 2015-11-25 at 17:30 +0000, Rainer Weikusat wrote:

> In case this is wrong, it obviously implies that sk_sleep(sk) must not
> be used anywhere as it accesses the same struck sock, hence, when that
> can "suddenly" disappear despite locks are used in the way indicated
> above, there is now safe way to invoke that, either, as it just does a
> rcu_dereference_raw based on the assumption that the caller knows that
> the i-node (and the corresponding wait queue) still exist.
> 

Oh well.

sk_sleep() is not used if the return is NULL

This is exactly why we have such code in critical functions :

wqueue = sk_sleep(sk);
if (wqueue && waitqueue_active(wqueue))
	wake_up_interruptible_poll(wqueue, 
				   POLLOUT | POLLWRNORM | POLLWRBAND);


We already took care of this problem years ago, but missed the ASYNC
case (that almost nobody really uses these days)



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