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From: Dmitry Vyukov <dvyukov@google.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
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: Mon, 20 Sep 2021 10:13:10 +0200	[thread overview]
Message-ID: <CACT4Y+aq+m8DkB+8Zvh0G5Ehmtd2kgapDr9eJEP0Mq5WLCOWMg@mail.gmail.com> (raw)
In-Reply-To: <20210916162850.GQ3544071@ziepe.ca>

On Thu, 16 Sept 2021 at 18:28, Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Thu, Sep 16, 2021 at 04:45:27PM +0200, Dmitry Vyukov wrote:
>
> > 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...
>
> I have a reasonable theory now..
>
> Based on the ops you provided this FSM sequence is possible
>
> RDMA_USER_CM_CMD_RESOLVE_IP
>   RDMA_CM_IDLE -> RDMA_CM_ADDR_QUERY
>   does rdma_resolve_ip(addr_handler)
>
>                           addr_handler
>                             RDMA_CM_ADDR_QUERY -> RDMA_CM_ADDR_BOUND
>                             [.. handler still running ..]
>
> RDMA_USER_CM_CMD_RESOLVE_IP
>   RDMA_CM_ADDR_BOUND -> RDMA_CM_ADDR_QUERY
>   does rdma_resolve_ip(addr_handler)
>
> RDMA_DESTROY_ID
>   rdma_addr_cancel()
>
> Which, if it happens fast enough, could trigger a situation where the
> '&id_priv->id.route.addr.dev_addr' "handle" is in the req_list twice
> beacause the addr_handler work queue hasn't yet got to the point of
> deleting it from the req_list before the the 2nd one is added.
>
> The issue is rdma_addr_cancel() has to be called rdma_resolve_ip() can
> be called again.
>
> Skipping it will cause 'req_list' to have two items in the internal
> linked list with the same key and it will not cancel the newest one
> with the active timer. This would cause the use after free syndrome
> like this trace is showing.
>
> I can make a patch, but have no way to know if it is any good :\

Good detective work!

But if you have a theory of what happens, it's usually easy to write a
reproducer that aims at triggering this exact scenario. Isn't it the
case here? I would assume you need it to add as a test anyway.

  reply	other threads:[~2021-09-20  8:13 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
2021-09-16 16:28         ` Jason Gunthorpe
2021-09-20  8:13           ` Dmitry Vyukov [this message]
     [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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