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Date:   Sat, 29 Jan 2022 12:41:51 +0100
From:   Greg KH <>
To:     Ziyang Xuan <>
Subject: Re: [PATCH 4.9] can: bcm: fix UAF of bcm op

On Fri, Jan 28, 2022 at 02:40:54PM +0800, Ziyang Xuan wrote:
> Stopping tasklet and hrtimer rely on the active state of tasklet and
> hrtimer sequentially in bcm_remove_op(), the op object will be freed
> if they are all unactive. Assume the hrtimer timeout is short, the
> hrtimer cb has been excuted after tasklet conditional judgment which
> must be false after last round tasklet_kill() and before condition
> hrtimer_active(), it is false when execute to hrtimer_active(). Bug
> is triggerd, because the stopping action is end and the op object
> will be freed, but the tasklet is scheduled. The resources of the op
> object will occur UAF bug.
> Move hrtimer_cancel() behind tasklet_kill() and switch 'while () {...}'
> to 'do {...} while ()' to fix the op UAF problem.
> Fixes: a06393ed0316 ("can: bcm: fix hrtimer/tasklet termination in bcm op removal")
> Reported-by:
> Cc:
> Signed-off-by: Ziyang Xuan <>
> ---
>  net/can/bcm.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)

Both now queued up, thanks.

greg k-h

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