netdev - Re: [PATCH net] can: bcm: switch timer to HRTIMER_MODE_SOFT and remove hrtimer

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Date:   Thu, 13 Jan 2022 11:49:36 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>
Cc:     davem@...emloft.net, kuba@...nel.org, socketcan@...tkopp.net,
        mkl@...gutronix.de, netdev@...r.kernel.org, stable@...r.kernel.org,
        linux-can@...r.kernel.org, tglx@...utronix.de,
        anna-maria@...utronix.de
Subject: Re: [PATCH net] can: bcm: switch timer to HRTIMER_MODE_SOFT and
 remove hrtimer_tasklet

On Tue, Jan 11, 2022 at 10:02:09AM +0800, Ziyang Xuan (William) wrote:
> > On Mon, Jan 10, 2022 at 09:23:22PM +0800, Ziyang Xuan wrote:
> >> From: Thomas Gleixner <tglx@...utronix.de>
> >>
> >> [ commit bf74aa86e111aa3b2fbb25db37e3a3fab71b5b68 upstream ]
> >>
> >> Stop tx/rx cycle 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.
> > 
> > That is not the changelog text of this commit.  Why modify it?
> 
> Above statement is the reason why I want to backport the patch to
> stable tree. Maybe I could give an extra cover-letter to explain
> the details of the problem, but modify the original changelog. Is it?
> 
> > 
> >>
> >> ----------------------------------------------------------------------
> >>
> >> This patch switches the timer to HRTIMER_MODE_SOFT, which executed the
> >> timer callback in softirq context and removes the hrtimer_tasklet.
> >>
> >> Reported-by: syzbot+652023d5376450cc8516@...kaller.appspotmail.com
> 
> This is the public problem reporter. Do I need to move it to cover-letter
> but here?
> 
> >> Cc: stable@...r.kernel.org # 4.19
> 
> I want to backport the patch to linux-4.19.y stable tree. How do I need to
> modify?

No need, I can take it like this, thanks.

greg k-h