From: Muchun Song <songmuchun@bytedance.com>
Date: Thu, 23 Mar 2023 10:50:03 +0800
Subject: [PATCH] mm: kfence: fix handling discontiguous page
References: bsc#1012628
Patch-mainline: 6.2.11
Git-commit: 1f2803b2660f4b04d48d065072c0ae0c9ca255fd

commit 1f2803b2660f4b04d48d065072c0ae0c9ca255fd upstream.

The struct pages could be discontiguous when the kfence pool is allocated
via alloc_contig_pages() with CONFIG_SPARSEMEM and
!CONFIG_SPARSEMEM_VMEMMAP.

This may result in setting PG_slab and memcg_data to a arbitrary
address (may be not used as a struct page), which in the worst case
might corrupt the kernel.

So the iteration should use nth_page().

Link: https://lkml.kernel.org/r/20230323025003.94447-1-songmuchun@bytedance.com
Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: SeongJae Park <sjpark@amazon.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 mm/kfence/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index d66092dd..1065e056 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -556,7 +556,7 @@ static unsigned long kfence_init_pool(void)
 	 * enters __slab_free() slow-path.
 	 */
 	for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
-		struct slab *slab = page_slab(&pages[i]);
+		struct slab *slab = page_slab(nth_page(pages, i));
 
 		if (!i || (i % 2))
 			continue;
@@ -602,7 +602,7 @@ static unsigned long kfence_init_pool(void)
 
 reset_slab:
 	for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
-		struct slab *slab = page_slab(&pages[i]);
+		struct slab *slab = page_slab(nth_page(pages, i));
 
 		if (!i || (i % 2))
 			continue;
-- 
2.35.3