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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: syzbot <syzbot+dc3dfba010d7671e05f5@syzkaller.appspotmail.com>,
	dledford@redhat.com, leon@kernel.org,
	linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
	syzkaller-bugs@googlegroups.com,
	Aleksandr Nogikh <nogikh@google.com>
Subject: Re: [syzbot] KASAN: use-after-free Read in addr_handler (4)
Date: Thu, 16 Sep 2021 13:02:24 -0300	[thread overview]
Message-ID: <20210916160224.GP3544071@ziepe.ca> (raw)
In-Reply-To: <CACT4Y+aUFbj3_+iBpeP2qrQ=RbGrssr0-6EZv1nx73at7fdbfA@mail.gmail.com>

On Thu, Sep 16, 2021 at 04:45:27PM +0200, Dmitry Vyukov wrote:

> It looks like a very hard to trigger race (few crashes, no reproducer,
> but KASAN reports look sensible). That's probably the reason syzkaller
> can't create a reproducer.
> From the log it looks like it was triggered by one of these programs
> below. But I tried to reproduce manually and had no success.
> We are currently doing some improvements to race triggering code in
> syzkaller, and may try to use this as a litmus test to see if
> syzkaller will do any better:
> https://github.com/google/syzkaller/issues/612#issuecomment-920961538

I would suggest to look at this:

https://patchwork.kernel.org/project/linux-rdma/patch/0-v1-9fbb33f5e201+2a-cma_listen_jgg@nvidia.com/

Which I think should be completely deterministic, just do the RDMA_CM
ops in the right order, but syzbot didn't find a reproducer.

The "healer" fork did however:

https://lore.kernel.org/all/CACkBjsY-CNzO74XGo0uJrcaZTubC+Yw9Sg1bNNi+evUOGaZTCg@mail.gmail.com/#r

> Answering your question re what was running concurrently with what.
> Each of the syscalls in these programs can run up to 2 times and
> ultimately any of these calls can race with any. Potentially syzkaller
> can predict values kernel will return (e.g. id's) before kernel
> actually returned them. I guess this does not restrict search area for
> the bug a lot...

Well, it does help if it is only those system calls

And I think I can discount the workqueue as a problem as I'd expect a
kasn hit on the 'req' allocation if the workqueue was malfunctioning -
thus I must conclude we are not calling work cancelation for some
reason.

Jason

  parent reply	other threads:[~2021-09-16 16:02 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-15 12:41 syzbot
2021-09-15 19:36 ` Jason Gunthorpe
2021-09-16  7:43   ` Dmitry Vyukov
2021-09-16 13:04     ` Jason Gunthorpe
2021-09-16 14:45       ` Dmitry Vyukov
2021-09-16 14:47         ` Dmitry Vyukov
2021-09-16 14:55           ` Dmitry Vyukov
2021-09-16 15:08             ` Jason Gunthorpe
2021-09-16 15:17               ` Dmitry Vyukov
2021-09-16 16:02         ` Jason Gunthorpe [this message]
2021-09-16 16:28         ` Jason Gunthorpe
2021-09-20  8:13           ` Dmitry Vyukov
     [not found]           ` <20211005032901.1876-1-hdanton@sina.com>
2021-10-05 12:23             ` Jason Gunthorpe
     [not found]             ` <20211006031800.2066-1-hdanton@sina.com>
2021-10-06 11:41               ` Jason Gunthorpe

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