From: Peng Fan <peng.fan@xxxxxxx>
With 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
redzones. But (in check_object()) when orig_size is set to zero, the entire
object is perceived as a redzone. To a valid allocated kmalloc space,
when init_on_free=1, the wasted space and the orig_size should
not be cleared to 0, otherwise there will be kernel dump:
[ 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")
Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
---
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 | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 94f5a4143825..a5fbeb2835b1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1895,6 +1895,15 @@ static inline void inc_slabs_node(struct kmem_cache *s, int node,
static inline void dec_slabs_node(struct kmem_cache *s, int node,
int objects) {}
+static inline unsigned int get_orig_size(struct kmem_cache *s, void *object)
+{
+ return s->object_size;
+}
+
+static inline void set_orig_size(struct kmem_cache *s, void *object,
+ unsigned int orig_size)
+{}
+
#ifndef CONFIG_SLUB_TINY
static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
void **freelist, void *nextfree)
@@ -2282,14 +2291,21 @@ 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
