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authorKees Cook <keescook@chromium.org>2021-06-15 18:23:26 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-06-16 09:24:42 -0700
commite41a49fadbc80b60b48d3c095d9e2ee7ef7c9a8e (patch)
tree8e419e9ec3faa2d56987d65e4b3a1e1e82dbe08b
parent74c1d3e081533825f2611e46edea1fcdc0701985 (diff)
mm/slub: actually fix freelist pointer vs redzoning
It turns out that SLUB redzoning ("slub_debug=Z") checks from s->object_size rather than from s->inuse (which is normally bumped to make room for the freelist pointer), so a cache created with an object size less than 24 would have the freelist pointer written beyond s->object_size, causing the redzone to be corrupted by the freelist pointer. This was very visible with "slub_debug=ZF": BUG test (Tainted: G B ): Right Redzone overwritten ----------------------------------------------------------------------------- INFO: 0xffff957ead1c05de-0xffff957ead1c05df @offset=1502. First byte 0x1a instead of 0xbb INFO: Slab 0xffffef3950b47000 objects=170 used=170 fp=0x0000000000000000 flags=0x8000000000000200 INFO: Object 0xffff957ead1c05d8 @offset=1496 fp=0xffff957ead1c0620 Redzone (____ptrval____): bb bb bb bb bb bb bb bb ........ Object (____ptrval____): 00 00 00 00 00 f6 f4 a5 ........ Redzone (____ptrval____): 40 1d e8 1a aa @.... Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........ Adjust the offset to stay within s->object_size. (Note that no caches of in this size range are known to exist in the kernel currently.) Link: https://lkml.kernel.org/r/20210608183955.280836-4-keescook@chromium.org Link: https://lore.kernel.org/linux-mm/20200807160627.GA1420741@elver.google.com/ Link: https://lore.kernel.org/lkml/0f7dd7b2-7496-5e2d-9488-2ec9f8e90441@suse.cz/Fixes: 89b83f282d8b (slub: avoid redzone when choosing freepointer location) Link: https://lore.kernel.org/lkml/CANpmjNOwZ5VpKQn+SYWovTkFB4VsT-RPwyENBmaK0dLcpqStkA@mail.gmail.com Signed-off-by: Kees Cook <keescook@chromium.org> Reported-by: Marco Elver <elver@google.com> Reported-by: "Lin, Zhenpeng" <zplin@psu.edu> Tested-by: Marco Elver <elver@google.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Christoph Lameter <cl@linux.com> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Roman Gushchin <guro@fb.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/slub.c14
1 files changed, 3 insertions, 11 deletions
diff --git a/mm/slub.c b/mm/slub.c
index f58cfd456548..fe30df460fad 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3689,7 +3689,6 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
{
slab_flags_t flags = s->flags;
unsigned int size = s->object_size;
- unsigned int freepointer_area;
unsigned int order;
/*
@@ -3698,13 +3697,6 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
* the possible location of the free pointer.
*/
size = ALIGN(size, sizeof(void *));
- /*
- * This is the area of the object where a freepointer can be
- * safely written. If redzoning adds more to the inuse size, we
- * can't use that portion for writing the freepointer, so
- * s->offset must be limited within this for the general case.
- */
- freepointer_area = size;
#ifdef CONFIG_SLUB_DEBUG
/*
@@ -3730,7 +3722,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
/*
* With that we have determined the number of bytes in actual use
- * by the object. This is the potential offset to the free pointer.
+ * by the object and redzoning.
*/
s->inuse = size;
@@ -3753,13 +3745,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
*/
s->offset = size;
size += sizeof(void *);
- } else if (freepointer_area > sizeof(void *)) {
+ } else {
/*
* Store freelist pointer near middle of object to keep
* it away from the edges of the object to avoid small
* sized over/underflows from neighboring allocations.
*/
- s->offset = ALIGN(freepointer_area / 2, sizeof(void *));
+ s->offset = ALIGN_DOWN(s->object_size / 2, sizeof(void *));
}
#ifdef CONFIG_SLUB_DEBUG