From: Peng Fan <peng.fan@xxxxxxx>
Since commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra
allocated kmalloc space than requested"), setting orig_size treats
the wasted space (object_size - orig_size) as a redzone. However with
init_on_free=1 we clear the full object->size, including the redzone.
Additionally we clear the object metadata, including the stored orig_size,
making it zero, which makes check_object() treat the whole object as a
redzone.
These issues lead to the following BUG report with "slub_debug=FUZ
init_on_free=1":
[ 0.000000] =============================================================================
[ 0.000000] BUG kmalloc-8 (Not tainted): kmalloc Redzone overwritten
[ 0.000000] -----------------------------------------------------------------------------
[ 0.000000]
[ 0.000000] 0xffff000010032858-0xffff00001003285f @offset=2136. First byte 0x0 instead of 0xcc
[ 0.000000] FIX kmalloc-8: Restoring kmalloc Redzone 0xffff000010032858-0xffff00001003285f=0xcc
[ 0.000000] Slab 0xfffffdffc0400c80 objects=36 used=23 fp=0xffff000010032a18 flags=0x3fffe0000000200(workingset|node=0|zone=0|lastcpupid=0x1ffff)
[ 0.000000] Object 0xffff000010032858 @offset=2136 fp=0xffff0000100328c8
[ 0.000000]
[ 0.000000] Redzone ffff000010032850: cc cc cc cc cc cc cc cc ........
[ 0.000000] Object ffff000010032858: cc cc cc cc cc cc cc cc ........
[ 0.000000] Redzone ffff000010032860: cc cc cc cc cc cc cc cc ........
[ 0.000000] Padding ffff0000100328b4: 00 00 00 00 00 00 00 00 00 00 00 00 ............
[ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.11.0-rc3-next-20240814-00004-g61844c55c3f4 #144
[ 0.000000] Hardware name: NXP i.MX95 19X19 board (DT)
[ 0.000000] Call trace:
[ 0.000000] dump_backtrace+0x90/0xe8
[ 0.000000] show_stack+0x18/0x24
[ 0.000000] dump_stack_lvl+0x74/0x8c
[ 0.000000] dump_stack+0x18/0x24
[ 0.000000] print_trailer+0x150/0x218
[ 0.000000] check_object+0xe4/0x454
[ 0.000000] free_to_partial_list+0x2f8/0x5ec
To address the issue, use orig_size to clear the used area. And restore
the value of orig_size after clear the remaining area.
When CONFIG_SLUB_DEBUG not defined, (get_orig_size()' directly returns
s->object_size. So when using memset to init the area, the size can simply
be orig_size, as orig_size returns object_size when CONFIG_SLUB_DEBUG not
enabled. And orig_size can never be bigger than object_size.
Fixes: 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested")
Reviewed-by: Feng Tang <feng.tang@xxxxxxxxx>
Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
---
V1->V2:
Update commit log (Per Vlastimil)
Move get_orig_size/set_orig_size out of CONFIG_SLUB_DEBUG (Per Vlastimil and Feng)
Add R-b from Feng
RFC->V1:
Update commit log (Per Hyeonggon)
Use orig_size to do memset(Per Hyeonggon)
Add get_orig_size and set_orig_size when CONFIG_SLUB_DEBUG not enabled(kernel test robot)
https://lore.kernel.org/all/20240819064115.385086-1-peng.fan@xxxxxxxxxxx/
mm/slub.c | 100 +++++++++++++++++++++++++++++-------------------------
1 file changed, 53 insertions(+), 47 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 668ea1e998a4..d63f39a5a1f8 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -756,6 +756,50 @@ static inline bool slab_update_freelist(struct kmem_cache *s, struct slab *slab,
return false;
}
+/*
+ * kmalloc caches has fixed sizes (mostly power of 2), and kmalloc() API
+ * family will round up the real request size to these fixed ones, so
+ * there could be an extra area than what is requested. Save the original
+ * request size in the meta data area, for better debug and sanity check.
+ */
+static inline void set_orig_size(struct kmem_cache *s,
+ void *object, unsigned int orig_size)
+{
+ void *p = kasan_reset_tag(object);
+ unsigned int kasan_meta_size;
+
+ if (!slub_debug_orig_size(s))
+ return;
+
+ /*
+ * KASAN can save its free meta data inside of the object at offset 0.
+ * If this meta data size is larger than 'orig_size', it will overlap
+ * the data redzone in [orig_size+1, object_size]. Thus, we adjust
+ * 'orig_size' to be as at least as big as KASAN's meta data.
+ */
+ kasan_meta_size = kasan_metadata_size(s, true);
+ if (kasan_meta_size > orig_size)
+ orig_size = kasan_meta_size;
+
+ p += get_info_end(s);
+ p += sizeof(struct track) * 2;
+
+ *(unsigned int *)p = orig_size;
+}
+
+static inline unsigned int get_orig_size(struct kmem_cache *s, void *object)
+{
+ void *p = kasan_reset_tag(object);
+
+ if (!slub_debug_orig_size(s))
+ return s->object_size;
+
+ p += get_info_end(s);
+ p += sizeof(struct track) * 2;
+
+ return *(unsigned int *)p;
+}
+
#ifdef CONFIG_SLUB_DEBUG
static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
static DEFINE_SPINLOCK(object_map_lock);
@@ -985,50 +1029,6 @@ static void print_slab_info(const struct slab *slab)
&slab->__page_flags);
}
-/*
- * kmalloc caches has fixed sizes (mostly power of 2), and kmalloc() API
- * family will round up the real request size to these fixed ones, so
- * there could be an extra area than what is requested. Save the original
- * request size in the meta data area, for better debug and sanity check.
- */
-static inline void set_orig_size(struct kmem_cache *s,
- void *object, unsigned int orig_size)
-{
- void *p = kasan_reset_tag(object);
- unsigned int kasan_meta_size;
-
- if (!slub_debug_orig_size(s))
- return;
-
- /*
- * KASAN can save its free meta data inside of the object at offset 0.
- * If this meta data size is larger than 'orig_size', it will overlap
- * the data redzone in [orig_size+1, object_size]. Thus, we adjust
- * 'orig_size' to be as at least as big as KASAN's meta data.
- */
- kasan_meta_size = kasan_metadata_size(s, true);
- if (kasan_meta_size > orig_size)
- orig_size = kasan_meta_size;
-
- p += get_info_end(s);
- p += sizeof(struct track) * 2;
-
- *(unsigned int *)p = orig_size;
-}
-
-static inline unsigned int get_orig_size(struct kmem_cache *s, void *object)
-{
- void *p = kasan_reset_tag(object);
-
- if (!slub_debug_orig_size(s))
- return s->object_size;
-
- p += get_info_end(s);
- p += sizeof(struct track) * 2;
-
- return *(unsigned int *)p;
-}
-
void skip_orig_size_check(struct kmem_cache *s, const void *object)
{
set_orig_size(s, (void *)object, s->object_size);
@@ -1894,7 +1894,6 @@ static inline void inc_slabs_node(struct kmem_cache *s, int node,
int objects) {}
static inline void dec_slabs_node(struct kmem_cache *s, int node,
int objects) {}
-
#ifndef CONFIG_SLUB_TINY
static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
void **freelist, void *nextfree)
@@ -2286,14 +2285,21 @@ bool slab_free_hook(struct kmem_cache *s, void *x, bool init,
*/
if (unlikely(init)) {
int rsize;
- unsigned int inuse;
+ unsigned int inuse, orig_size;
inuse = get_info_end(s);
+ orig_size = get_orig_size(s, x);
if (!kasan_has_integrated_init())
- memset(kasan_reset_tag(x), 0, s->object_size);
+ memset(kasan_reset_tag(x), 0, orig_size);
rsize = (s->flags & SLAB_RED_ZONE) ? s->red_left_pad : 0;
memset((char *)kasan_reset_tag(x) + inuse, 0,
s->size - inuse - rsize);
+ /*
+ * Restore orig_size, otherwize kmalloc redzone overwritten
+ * would be reported
+ */
+ set_orig_size(s, x, orig_size);
+
}
/* KASAN might put x into memory quarantine, delaying its reuse. */
return !kasan_slab_free(s, x, init, still_accessible);
--
2.37.1
