[PATCH 5.12 091/127] userfaultfd: hugetlbfs: fix new flag usage in error path

Greg Kroah-Hartman
2021-05-24T16:06:05Z

From: Mike Kravetz <mike.kravetz@oracle.com>

commit e32905e57358fdfb82f9de024534f205b3af7dac upstream.

In commit d6995da31122 ("hugetlb: use page.private for hugetlb specific
page flags") the use of PagePrivate to indicate a reservation count
should be restored at free time was changed to the hugetlb specific flag
HPageRestoreReserve. Changes to a userfaultfd error path as well as a
VM_BUG_ON() in remove_inode_hugepages() were overlooked.

Users could see incorrect hugetlb reserve counts if they experience an
error with a UFFDIO_COPY operation. Specifically, this would be the
result of an unlikely copy_huge_page_from_user error. There is not an
increased chance of hitting the VM_BUG_ON.

Link: https://lkml.kernel.org/r/20210521233952.236434-1-mike.kravetz@oracle.com
Fixes: d6995da31122 ("hugetlb: use page.private for hugetlb specific page flags")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Mina Almasry <almasry.mina@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/hugetlbfs/inode.c | 2 +-
mm/userfaultfd.c | 28 ++++++++++++++--------------
2 files changed, 15 insertions(+), 15 deletions(-)

--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -532,7 +532,7 @@ static void remove_inode_hugepages(struc
* the subpool and global reserve usage count can need
* to be adjusted.
*/
- VM_BUG_ON(PagePrivate(page));
+ VM_BUG_ON(HPageRestoreReserve(page));
remove_huge_page(page);
freed++;
if (!truncate_op) {
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -362,38 +362,38 @@ out:
* If a reservation for the page existed in the reservation
* map of a private mapping, the map was modified to indicate
* the reservation was consumed when the page was allocated.
- * We clear the PagePrivate flag now so that the global
+ * We clear the HPageRestoreReserve flag now so that the global
* reserve count will not be incremented in free_huge_page.
* The reservation map will still indicate the reservation
* was consumed and possibly prevent later page allocation.
* This is better than leaking a global reservation. If no
- * reservation existed, it is still safe to clear PagePrivate
- * as no adjustments to reservation counts were made during
- * allocation.
+ * reservation existed, it is still safe to clear
+ * HPageRestoreReserve as no adjustments to reservation counts
+ * were made during allocation.
*
* The reservation map for shared mappings indicates which
* pages have reservations. When a huge page is allocated
* for an address with a reservation, no change is made to
- * the reserve map. In this case PagePrivate will be set
- * to indicate that the global reservation count should be
+ * the reserve map. In this case HPageRestoreReserve will be
+ * set to indicate that the global reservation count should be
* incremented when the page is freed. This is the desired
* behavior. However, when a huge page is allocated for an
* address without a reservation a reservation entry is added
- * to the reservation map, and PagePrivate will not be set.
- * When the page is freed, the global reserve count will NOT
- * be incremented and it will appear as though we have leaked
- * reserved page. In this case, set PagePrivate so that the
- * global reserve count will be incremented to match the
- * reservation map entry which was created.
+ * to the reservation map, and HPageRestoreReserve will not be
+ * set. When the page is freed, the global reserve count will
+ * NOT be incremented and it will appear as though we have
+ * leaked reserved page. In this case, set HPageRestoreReserve
+ * so that the global reserve count will be incremented to
+ * match the reservation map entry which was created.
*
* Note that vm_alloc_shared is based on the flags of the vma
* for which the page was originally allocated. dst_vma could
* be different or NULL on error.
*/
if (vm_alloc_shared)
- SetPagePrivate(page);
+ SetHPageRestoreReserve(page);
else
- ClearPagePrivate(page);
+ ClearHPageRestoreReserve(page);
put_page(page);
}
BUG_ON(copied < 0);