Re: [PATCH -next] hugetlb_cgroup: fix illegal access to memory

[Mina Almasry <almasrymina@google.com>]

Tejun/Mike you want to also give this a quick look?

On Sat, Mar 14, 2020 at 11:21 AM Giuseppe Scrivano <gscrivan@redhat.com> wrote:
>
> Mina Almasry <almasrymina@google.com> writes:
>
> > On Fri, Mar 13, 2020 at 3:39 PM Mina Almasry <almasrymina@google.com> wrote:
> >>
> >> This appears to be a mistake in commit faced7e0806cf ("mm: hugetlb
> >> controller for cgroups v2"). Essentially that commit does
> >> a hugetlb_cgroup_from_counter assuming that page_counter_try_charge has
> >> initialized counter, but if page_counter_try_charge has failed then it
> >> seems it does not initialize counter, so
> >> hugetlb_cgroup_from_counter(counter) ends up pointing to random memory,
> >> causing kasan to complain.
> >>
> >> Solution, simply use h_cg, instead of
> >> hugetlb_cgroup_from_counter(counter), since that is a reference to the
> >> hugetlb_cgroup anyway. After this change kasan ceases to complain.
> >>
> >> Signed-off-by: Mina Almasry <almasrymina@google.com>
> >> Reported-by: syzbot+cac0c4e204952cf449b1@syzkaller.appspotmail.com
> >> Fixes: commit faced7e0806cf ("mm: hugetlb controller for cgroups v2")
> >> Cc: Andrew Morton <akpm@linux-foundation.org>
> >> Cc: linux-mm@kvack.org
> >> Cc: linux-kernel@vger.kernel.org
> >> Cc: Giuseppe Scrivano <gscrivan@redhat.com>
> >> Cc: Tejun Heo <tj@kernel.org>
> >> Cc: mike.kravetz@oracle.com
> >> Cc: rientjes@google.com
> >>
> >> ---
> >>  mm/hugetlb_cgroup.c | 3 +--
> >>  1 file changed, 1 insertion(+), 2 deletions(-)
> >>
> >> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
> >> index 7994eb8a2a0b4..aabf65d4d91ba 100644
> >> --- a/mm/hugetlb_cgroup.c
> >> +++ b/mm/hugetlb_cgroup.c
> >> @@ -259,8 +259,7 @@ static int __hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
> >>                     __hugetlb_cgroup_counter_from_cgroup(h_cg, idx, rsvd),
> >>                     nr_pages, &counter)) {
> >>                 ret = -ENOMEM;
> >> -               hugetlb_event(hugetlb_cgroup_from_counter(counter, idx), idx,
> >> -                             HUGETLB_MAX);
> >> +               hugetlb_event(h_cg, idx, HUGETLB_MAX);
> >>                 css_put(&h_cg->css);
> >>                 goto done;
> >>         }
> >> --
> >> 2.25.1.481.gfbce0eb801-goog
>
> Acked-by: Giuseppe Scrivano <gscrivan@redhat.com>
>
> Thanks,
> Giuseppe
>