linux-kernel - Re: use-after-free in sock_wake

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Message-ID: <1448558959.24696.91.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 26 Nov 2015 09:29:19 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Rainer Weikusat <rweikusat@...ileactivedefense.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Benjamin LaHaise <bcrl@...ck.org>,
	"David S. Miller" <davem@...emloft.net>,
	Al Viro <viro@...iv.linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Ying Xue <ying.xue@...driver.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in sock_wake_async

On Thu, 2015-11-26 at 18:03 +0100, Hannes Frederic Sowa wrote:

> Also isn't the reason why slub exists so it can track memory regions
> per-cpu.

call_rcu() and kfree_rcu() will add a grace period (multiple ms) where
the cpu will likely evict from its caches the data contained in the
'about to be freed' objects, defeating the SLUB/SLAB ability to quickly
reuse a freed and hot object (LIFO)

This is one of the major RCU drawback : Force a FIFO behavior in object
reuse while LIFO one is much better for data locality, especially with
per-cpu lists.

Another problem is a slightly bigger working set size, which can hurt
some workloads that used to exactly fit cpu caches.


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