mm: kfence: fix handling discontiguous page

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>

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index d66092dd187c8b4f5da9aa98cf6584330ce085e5..1065e0568d05a350641b4cbb6fce7ef7c808203b 100644 (file)
--- 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;