linux-kernel - Re: [PATCH 4.14 2/2] can: bcm: fix UAF of bcm op

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Date:   Fri, 4 Feb 2022 07:59:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+5ca851459ed04c778d1d@...kaller.appspotmail.com,
        Ziyang Xuan <william.xuanziyang@...wei.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>
Subject: Re: [PATCH 4.14 2/2] can: bcm: fix UAF of bcm op

On Thu, Feb 03, 2022 at 09:45:18PM +0100, Pavel Machek wrote:
> Hi!
> 
> 
> > From: Ziyang Xuan <william.xuanziyang@...wei.com>
> > 
> > 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.
> 
> I don't see this commit in mainline or next kernels. What is going on
> here? Is it one of those "only needed in -stable" things? Or do we
> still need to fix it in the mainline?

Please see the stable list discussion of this commit for other branches,
it should answer your question.

thanks,

greg k-h