+ mm-z3fold-avoid-possible-underflow-in-z3fold_alloc.patch added to -mm tree

+ mm-z3fold-avoid-possible-underflow-in-z3fold_alloc.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/z3fold: avoid possible underflow in z3fold_alloc()
has been added to the -mm tree.  Its filename is
     mm-z3fold-avoid-possible-underflow-in-z3fold_alloc.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-z3fold-avoid-possible-underflow-in-z3fold_alloc.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-z3fold-avoid-possible-underflow-in-z3fold_alloc.patch

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------------------------------------------------------
From: Miaohe Lin <linmiaohe@huawei.com>
Subject: mm/z3fold: avoid possible underflow in z3fold_alloc()

It is not enough to just make sure the z3fold header is not larger than
the page size.  When z3fold header is equal to PAGE_SIZE, we would
underflow when check alloc size against PAGE_SIZE - ZHDR_SIZE_ALIGNED -
CHUNK_SIZE in z3fold_alloc().  Make sure there has remaining spaces for
its buddy to fix this theoretical issue.

Link: https://lkml.kernel.org/r/20210619093151.1492174-3-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Hillf Danton <hdanton@sina.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/z3fold.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/mm/z3fold.c~mm-z3fold-avoid-possible-underflow-in-z3fold_alloc
+++ a/mm/z3fold.c
@@ -1803,8 +1803,11 @@ static int __init init_z3fold(void)
 {
 	int ret;
 
-	/* Make sure the z3fold header is not larger than the page size */
-	BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
+	/*
+	 * Make sure the z3fold header is not larger than the page size and
+	 * there has remaining spaces for its buddy.
+	 */
+	BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE);
 	ret = z3fold_mount();
 	if (ret)
 		return ret;
_

Patches currently in -mm which might be from linmiaohe@huawei.com are

mm-swapfile-use-percpu_ref-to-serialize-against-concurrent-swapoff.patch
swap-fix-do_swap_page-race-with-swapoff.patch
mm-swap-remove-confusing-checking-for-non_swap_entry-in-swap_ra_info.patch
mm-shmem-fix-shmem_swapin-race-with-swapoff.patch
mm-swapfile-move-get_swap_page_of_type-under-config_hibernation.patch
mm-swapfile-move-get_swap_page_of_type-under-config_hibernation-fix.patch
mm-swapfile-move-get_swap_page_of_type-under-config_hibernation-fix-2.patch
mm-swap-remove-unused-local-variable-nr_shadows.patch
mm-swap_slotsc-delete-meaningless-forward-declarations.patch
mm-huge_memoryc-remove-dedicated-macro-hpage_cache_index_mask.patch
mm-huge_memoryc-use-page-deferred_list.patch
mm-huge_memoryc-add-missing-read-only-thp-checking-in-transparent_hugepage_enabled.patch
mm-huge_memoryc-add-missing-read-only-thp-checking-in-transparent_hugepage_enabled-v4.patch
mm-huge_memoryc-remove-unnecessary-tlb_remove_page_size-for-huge-zero-pmd.patch
mm-huge_memoryc-dont-discard-hugepage-if-other-processes-are-mapping-it.patch
mm-z3fold-define-macro-nchunks-as-total_chunks-zhdr_chunks.patch
mm-z3fold-avoid-possible-underflow-in-z3fold_alloc.patch
mm-z3fold-remove-magic-number-in-z3fold_create_pool.patch
mm-z3fold-remove-unused-function-handle_to_z3fold_header.patch
mm-z3fold-fix-potential-memory-leak-in-z3fold_destroy_pool.patch
mm-z3fold-use-release_z3fold_page_locked-to-release-locked-z3fold-page.patch
mm-zbud-reuse-unbuddied-as-buddied-in-zbud_pool.patch
mm-zbud-dont-export-any-zbud-api.patch
mm-zswapc-remove-unused-function-zswap_debugfs_exit.patch
mm-zswapc-avoid-unnecessary-copy-in-at-map-time.patch
mm-zswapc-fix-two-bugs-in-zswap_writeback_entry.patch