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

[Mina Almasry]

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@xxxxxxxxxx>
Reported-by: syzbot+cac0c4e204952cf449b1@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: commit faced7e0806cf ("mm: hugetlb controller for cgroups v2")
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: mike.kravetz@xxxxxxxxxx
Cc: rientjes@xxxxxxxxxx

---
 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