Re: [PATCH 4.14] can: bcm: fix UAF of bcm op

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Jan 23, 2022 at 03:10:01PM +0100, Oliver Hartkopp wrote:
> 
> 
> On 22.01.22 11:30, Greg KH wrote:
> > On Sat, Jan 22, 2022 at 06:25:06PM +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: syzbot+5ca851459ed04c778d1d@syzkaller.appspotmail.com
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
> > > ---
> > >   net/can/bcm.c | 20 ++++++++++----------
> > >   1 file changed, 10 insertions(+), 10 deletions(-)
> > 
> > What is the git commit id of this change in Linus's tree?
> 
> Linus' tree has been fixed by removing the tasklet implementation and
> replacing it with a HRTIMER_MODE_SOFT approach here:
> 
> commit bf74aa86e111a ("can: bcm: switch timer to HRTIMER_MODE_SOFT and
> remove hrtimer_tasklet")
> 
> This patch from Ziyang Xuan fixes the 'old' tasklet implementation for 'old'
> stable kernels that lack the HRTIMER_MODE_SOFT infrastructure.
> 
> Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>

Thanks, I'll queue this up for 4.14.

Ziyang, can I get a version for 4.19.y as well?

thanks,

greg k-h