Re: [PATCH net] can: bcm: switch timer to HRTIMER_MODE_SOFT and remove hrtimer_tasklet

["Ziyang Xuan (William)" <william.xuanziyang@huawei.com>]

> On Mon, Jan 10, 2022 at 09:23:22PM +0800, Ziyang Xuan wrote:
>> From: Thomas Gleixner <tglx@linutronix.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@syzkaller.appspotmail.com

This is the public problem reporter. Do I need to move it to cover-letter
but here?

>> Cc: stable@vger.kernel.org # 4.19

I want to backport the patch to linux-4.19.y stable tree. How do I need to
modify?

>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>> Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
>> Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
>> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
>> Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
>> ---
>>  net/can/bcm.c | 156 +++++++++++++++++---------------------------------
>>  1 file changed, 52 insertions(+), 104 deletions(-)
> 
> What stable kernel tree(s) are you wanting this backported to?
> 
> thanks,
> 
> greg k-h
> .
> 

Thank you for your patient guidance.