[patch 025/262] kasan: fix tag for large allocations when using CONFIG_SLAB

Andrew Morton
2021-11-05T20:35:56Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: kasan: fix tag for large allocations when using CONFIG_SLAB

If an object is allocated on a tail page of a multi-page slab, kasan will
get the wrong tag because page->s_mem is NULL for tail pages. I'm not
quite sure what the user-visible effect of this might be.

Link: https://lkml.kernel.org/r/20211001024105.3217339-1-willy@infradead.org
Fixes: 7f94ffbc4c6a ("kasan: add hooks implementation for tag-based mode")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Marco Elver <elver@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/kasan/common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/kasan/common.c~kasan-fix-tag-for-large-allocations-when-using-config_slab
+++ a/mm/kasan/common.c
@@ -298,7 +298,7 @@ static inline u8 assign_tag(struct kmem_
/* For caches that either have a constructor or SLAB_TYPESAFE_BY_RCU: */
#ifdef CONFIG_SLAB
/* For SLAB assign tags based on the object index in the freelist. */
- return (u8)obj_to_index(cache, virt_to_page(object), (void *)object);
+ return (u8)obj_to_index(cache, virt_to_head_page(object), (void *)object);
#else
/*
* For SLUB assign a random tag during slab creation, otherwise reuse
_