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From: Shuah Khan <>
To: Tetsuo Handa <>,
	Greg Kroah-Hartman <>,
	Valentina Manea <>,
	Shuah Khan <>,
	Shuah Khan <>
Cc: Hillf Danton <>,, Arnd Bergmann <>
Subject: Re: [PATCH] usb: usbip: fix error handling of kthread_get_run()
Date: Wed, 10 Feb 2021 11:11:17 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 2/5/21 6:08 PM, Tetsuo Handa wrote:
> On 2021/02/06 1:27, Shuah Khan wrote:
>> Good find. For this fix to be complete, you will have to add checks
>> for kthread_get_run() NULL return in attach_store() and
>> usbip_sockfd_store() routines in stub_dev.c and vudc_sysfs.c
> Initially I thought that the cleaner fix is to get kthread_create() out of kthread_get_run()
> ( the drivers/usb/usbip/vhci_sysfs.c portion in
> ) so that we can undo
> kthread_create() via kthread_stop(). But I found that such fix makes little sense because
> it is possible that SIGKILL is delivered between vhci_rx_loop() and vhci_tx_loop() have
> started and before leaving attach_store().
> Since the code prior to "staging/usbip: convert to kthread" was already capable of surviving
> such race condition, this patch should be already good enough for sending to stable kernels.
> Of course, since kthread_create() may return -ENOMEM without being SIGKILLed, we could update
> attach_store() to report kthread_get_run() failure to the caller, but that will be a separate
> patch. This patch alone avoids the crash although there is a hung task problem similar to
> remains
> ( ). The cause of hung
> task is currently unknown; maybe too much printk() messages.

I would like to see to see a complete fix. This patch changes
kthread_get_run() to return NULL. Without adding handling for
NULL in the callers of kthread_get_run(), we will start seeing

Does this patch fix the problem syzbot found?

-- Shuah

  reply	other threads:[~2021-02-10 18:14 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-20 18:44 KASAN: null-ptr-deref Write in vhci_shutdown_connection syzbot
2021-02-05 13:57 ` [PATCH] usb: usbip: fix error handling of kthread_get_run() Tetsuo Handa
2021-02-05 16:27   ` Shuah Khan
2021-02-06  1:08     ` Tetsuo Handa
2021-02-10 18:11       ` Shuah Khan [this message]
2021-02-10 18:16         ` Tetsuo Handa
2021-02-10 18:20           ` Shuah Khan
2021-02-10 18:43             ` Tetsuo Handa
2021-02-10 20:15               ` Shuah Khan
2021-02-11  1:04                 ` Tetsuo Handa
2021-02-11  3:01                   ` Tetsuo Handa
2021-02-11 13:40                     ` Tetsuo Handa

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