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From: Haakon Bugge <haakon.bugge@oracle.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Divya Indi <divya.indi@oracle.com>,
	LKML <linux-kernel@vger.kernel.org>,
	OFED mailing list <linux-rdma@vger.kernel.org>,
	Kaike Wan <kaike.wan@intel.com>,
	Gerd Rausch <gerd.rausch@oracle.com>,
	Srinivas Eeda <srinivas.eeda@oracle.com>,
	Rama Nichanamatlu <rama.nichanamatlu@oracle.com>,
	Doug Ledford <dledford@redhat.com>,
	Leon Romanovsky <leon@kernel.org>
Subject: Re: [PATCH v4] IB/sa: Resolving use-after-free in ib_nl_send_msg
Date: Thu, 26 Aug 2021 15:25:00 +0000	[thread overview]
Message-ID: <87E23BD6-857D-4A87-93EF-D2098535F997@oracle.com> (raw)
In-Reply-To: <20210825172629.GJ1721383@nvidia.com>



> On 25 Aug 2021, at 19:26, Jason Gunthorpe <jgg@nvidia.com> wrote:
> 
> On Mon, Aug 23, 2021 at 04:54:16PM +0000, Haakon Bugge wrote:
>> 
>> 
>>> On 8 Jul 2020, at 03:12, Jason Gunthorpe <jgg@nvidia.com> wrote:
>>> 
>>> On Tue, Jul 07, 2020 at 06:05:02PM -0700, Divya Indi wrote:
>>>> Thanks Jason.
>>>> 
>>>> Appreciate your help and feedback for fixing this issue.
>>>> 
>>>> Would it be possible to access the edited version of the patch?
>>>> If yes, please share a pointer to the same.
>>> 
>>> https://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git/commit/?h=for-rc&id=f427f4d6214c183c474eeb46212d38e6c7223d6a
>> 
>> Hi Jason,
>> 
>> 
>> At first glanse, this commit calls rdma_nl_multicast() whilst
>> holding a spinlock. Since rdma_nl_multicast() is called with a
>> gfp_flag parameter, one could assume it supports an atomic
>> context. rdma_nl_multicast() ends up in
>> netlink_broadcast_filtered(). This function calls
>> netlink_lock_table(), which calls read_unlock_irqrestore(), which
>> ends up calling _raw_read_unlock_irqrestore(). And here
>> preempt_enable() is called :-(
> 
> I don't understand. This:
> 
> 	unsigned long flags;
> 
> 	read_lock_irqsave(&nl_table_lock, flags);
> 	atomic_inc(&nl_table_users);
> 	read_unlock_irqrestore(&nl_table_lock, flags);
> 
> Is perfectly fine in an atomic context.
> 
> preempt_enable is implemented as a nesting counter, so it is fine to
> call it from inside an atomic region so long as it is balanced.

You are right. As I said, the stack trace was from a UEK kernel. It turns out, I overlooked commit 2dce224f469f ("netns: protect netns ID lookups with RCU"), which replaces spin_{lock,unlock}_bh with rcu_read_{lock,unlock} in peernet2id().

This commit fixed this bug un-intentionally, I would say! So, this bug has been present in kernels until v5.5-rc7.

Sorry for the noise!


Håkon



      reply	other threads:[~2021-08-26 15:25 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-24  2:13 Divya Indi
2020-06-25 10:09 ` Leon Romanovsky
2020-06-25 17:11   ` Divya Indi
2020-06-25 19:00     ` Leon Romanovsky
2020-07-02 19:07 ` Jason Gunthorpe
2020-07-08  1:05   ` Divya Indi
2020-07-08  1:12     ` Jason Gunthorpe
2021-08-23 16:54       ` Haakon Bugge
2021-08-25 17:26         ` Jason Gunthorpe
2021-08-26 15:25           ` Haakon Bugge [this message]

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