linux-kernel - [PATCH] mm/slub, kasan: fix checking page

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Date:   Wed, 11 Aug 2021 01:46:51 +0200
From:   andrey.konovalov@...ux.dev
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Shakeel Butt <shakeelb@...gle.com>
Subject: [PATCH] mm/slub, kasan: fix checking page_alloc allocations on free

From: Andrey Konovalov <andreyknvl@...il.com>

A fix for stat counters f227f0faf63b ("slub: fix unreclaimable slab stat
for bulk free") used page_address(page) as kfree_hook() argument instead
of object. While the change is technically correct, it breaks KASAN's
ability to detect improper (unaligned) pointers passed to kfree() and
causes the kmalloc_pagealloc_invalid_free test to fail.

This patch changes free_nonslab_page() to pass object to kfree_hook()
instead of page_address(page) as it was before the fix.

Fixed: f227f0faf63b ("slub: fix unreclaimable slab stat for bulk free")
Signed-off-by: Andrey Konovalov <andreyknvl@...il.com>
---
 mm/slub.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index af984e4990e8..56079dd33c74 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3236,12 +3236,12 @@ struct detached_freelist {
 	struct kmem_cache *s;
 };
 
-static inline void free_nonslab_page(struct page *page)
+static inline void free_nonslab_page(void *object, struct page *page)
 {
 	unsigned int order = compound_order(page);
 
 	VM_BUG_ON_PAGE(!PageCompound(page), page);
-	kfree_hook(page_address(page));
+	kfree_hook(object);
 	mod_lruvec_page_state(page, NR_SLAB_UNRECLAIMABLE_B, -(PAGE_SIZE << order));
 	__free_pages(page, order);
 }
@@ -3282,7 +3282,7 @@ int build_detached_freelist(struct kmem_cache *s, size_t size,
 	if (!s) {
 		/* Handle kalloc'ed objects */
 		if (unlikely(!PageSlab(page))) {
-			free_nonslab_page(page);
+			free_nonslab_page(object, page);
 			p[size] = NULL; /* mark object processed */
 			return size;
 		}
@@ -4258,7 +4258,7 @@ void kfree(const void *x)
 
 	page = virt_to_head_page(x);
 	if (unlikely(!PageSlab(page))) {
-		free_nonslab_page(page);
+		free_nonslab_page(object, page);
 		return;
 	}
 	slab_free(page->slab_cache, page, object, NULL, 1, _RET_IP_);
-- 
2.25.1