Re: [PATCH] sched/core: Fix a potential double fetch bug on attr->size

[Meng Xu]

Hi Peter,

I am sorry, I thought the patch is included in the forwarded
email. I just resent the patch. Please check.

Best Regards,
Meng

On 09/25/2017 03:31 AM, Peter Zijlstra wrote:
> On Sat, Sep 23, 2017 at 10:05:56PM -0400, Meng Xu wrote:
> > Hi Peter and Ingo,
> >
> > As a reminder, this is a very similar issue to perf_copy_attr (see following patch)
> > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=f12f42acdbb577a12eecfcebbbec41c81505c4dc <https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=f12f42acdbb577a12eecfcebbbec41c81505c4dc>
> >
> > Will it be fixed as well?
> If someone were to actually send me the patch.. probably.
>
> > > On Aug 29, 2017, at 3:10 PM, Meng Xu <meng.xu@xxxxxxxxxx> wrote:
> > >
> > > From: Meng Xu <mengxu.gatech@xxxxxxxxx>
> > >
> > > `attr->size` after the second fetch `copy_from_user(attr, uattr, size)`,
> > > can be different from what is initially fetched in and checked
> > > `get_user(size, &uattr->size)` by racing condition in the userspace.
> > >
> > > The issue and the patch are both similar to commit f12f42a
> > > (in kernel/events/core.c).
> > >
> > > Signed-off-by: Meng Xu <mengxu.gatech@xxxxxxxxx>
> > > ---
> > > kernel/sched/core.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > index 0869b20..c22d2b4 100644
> > > --- a/kernel/sched/core.c
> > > +++ b/kernel/sched/core.c
> > > @@ -4349,6 +4349,8 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
> > > 	if (ret)
> > > 		return -EFAULT;
> > >
> > > +	attr->size = size;
> > > +
> > > 	/*
> > > 	 * XXX: Do we want to be lenient like existing syscalls; or do we want
> > > 	 * to be strict and return an error on out-of-bounds values?
> > > --
> > > 2.7.4