linux-kernel - Re: [PATCH 4.19 016/133] cgroup: fix cgroup_sk_alloc() for sk_clone

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Date:   Thu, 13 Aug 2020 20:07:14 +0800
From:   Yang Yingliang <yangyingliang@...wei.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        "Cameron Berkenpas" <cam@...-zeon.de>,
        Peter Geis <pgwipeout@...il.com>,
        Lu Fengqi <lufq.fnst@...fujitsu.com>,
        Daniël Sonck <dsonck92@...il.com>,
        Zhang Qiang <qiang.zhang@...driver.com>,
        "Thomas Lamprecht" <t.lamprecht@...xmox.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Zefan Li <lizefan@...wei.com>, Tejun Heo <tj@...nel.org>,
        Roman Gushchin <guro@...com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 4.19 016/133] cgroup: fix cgroup_sk_alloc() for
 sk_clone_lock()


On 2020/8/13 19:41, Greg Kroah-Hartman wrote:
> On Thu, Aug 13, 2020 at 07:30:55PM +0800, Yang Yingliang wrote:
>> Hi,
>>
>> On 2020/7/20 23:36, Greg Kroah-Hartman wrote:
>>> From: Cong Wang <xiyou.wangcong@...il.com>
>>>
>>> [ Upstream commit ad0f75e5f57ccbceec13274e1e242f2b5a6397ed ]
>>>
>>> When we clone a socket in sk_clone_lock(), its sk_cgrp_data is
>>> copied, so the cgroup refcnt must be taken too. And, unlike the
>>> sk_alloc() path, sock_update_netprioidx() is not called here.
>>> Therefore, it is safe and necessary to grab the cgroup refcnt
>>> even when cgroup_sk_alloc is disabled.
>>>
>>> sk_clone_lock() is in BH context anyway, the in_interrupt()
>>> would terminate this function if called there. And for sk_alloc()
>>> skcd->val is always zero. So it's safe to factor out the code
>>> to make it more readable.
>>>
>>> The global variable 'cgroup_sk_alloc_disabled' is used to determine
>>> whether to take these reference counts. It is impossible to make
>>> the reference counting correct unless we save this bit of information
>>> in skcd->val. So, add a new bit there to record whether the socket
>>> has already taken the reference counts. This obviously relies on
>>> kmalloc() to align cgroup pointers to at least 4 bytes,
>>> ARCH_KMALLOC_MINALIGN is certainly larger than that.
>>>
>>> This bug seems to be introduced since the beginning, commit
>>> d979a39d7242 ("cgroup: duplicate cgroup reference when cloning sockets")
>>> tried to fix it but not compeletely. It seems not easy to trigger until
>>> the recent commit 090e28b229af
>>> ("netprio_cgroup: Fix unlimited memory leak of v2 cgroups") was merged.
>>>
>>> Fixes: bd1060a1d671 ("sock, cgroup: add sock->sk_cgroup")
>>> Reported-by: Cameron Berkenpas <cam@...-zeon.de>
>>> Reported-by: Peter Geis <pgwipeout@...il.com>
>>> Reported-by: Lu Fengqi <lufq.fnst@...fujitsu.com>
>>> Reported-by: Daniël Sonck <dsonck92@...il.com>
>>> Reported-by: Zhang Qiang <qiang.zhang@...driver.com>
>>> Tested-by: Cameron Berkenpas <cam@...-zeon.de>
>>> Tested-by: Peter Geis <pgwipeout@...il.com>
>>> Tested-by: Thomas Lamprecht <t.lamprecht@...xmox.com>
>>> Cc: Daniel Borkmann <daniel@...earbox.net>
>>> Cc: Zefan Li <lizefan@...wei.com>
>>> Cc: Tejun Heo <tj@...nel.org>
>>> Cc: Roman Gushchin <guro@...com>
>>> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
>>> Signed-off-by: David S. Miller <davem@...emloft.net>
>>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>> ---
>> [...]
>>> +void cgroup_sk_clone(struct sock_cgroup_data *skcd)
>>> +{
>>> +	/* Socket clone path */
>>> +	if (skcd->val) {
>> Compare to mainline patch, it's missing *if (skcd->no_refcnt)* check here.
>>
>> Is it a mistake here ?
> Possibly, it is in the cgroup_sk_free() call.  Can you send a patch to
> fix this up?

OK, I checked other stable branches, it also need be fixed in stable-4.9 
and stable-4.14.

I will send the patches to these branches.

>
> thanks,
>
> greg k-h
> .