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

[Giuseppe Scrivano <gscrivan@redhat.com>]

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