From: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
Commit 284f17ac13fe ("mm/slub: handle bulk and single object freeing
separately") splits single and bulk object freeing in two functions
slab_free() and slab_free_bulk() which leads slab_free() to call
slab_free_hook() directly instead of slab_free_freelist_hook().
If `init_on_free` is set, slab_free_hook() zeroes the object.
Afterward, if `slub_debug=F` and `CONFIG_SLAB_FREELIST_HARDENED` are
set, the do_slab_free() slowpath executes freelist consistency
checks and try to decode a zeroed freepointer which leads to a
"Freepointer corrupt" detection in check_object().
Object's freepointer thus needs to be avoided when stored outside the
object if init_on_free is set.
To reproduce, set `slub_debug=FU init_on_free=1 log_level=7` on the
command line of a kernel build with `CONFIG_SLAB_FREELIST_HARDENED=y`.
dmesg sample log:
[ 10.708715] =============================================================================
[ 10.710323] BUG kmalloc-rnd-05-32 (Tainted: G B T ): Freepointer corrupt
[ 10.712695] -----------------------------------------------------------------------------
[ 10.712695]
[ 10.712695] Slab 0xffffd8bdc400d580 objects=32 used=4 fp=0xffff9d9a80356f80 flags=0x200000000000a00(workingset|slab|node=0|zone=2)
[ 10.716698] Object 0xffff9d9a80356600 @offset=1536 fp=0x7ee4f480ce0ecd7c
[ 10.716698]
[ 10.716698] Bytes b4 ffff9d9a803565f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 10.720703] Object ffff9d9a80356600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 10.720703] Object ffff9d9a80356610: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 10.724696] Padding ffff9d9a8035666c: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 10.724696] Padding ffff9d9a8035667c: 00 00 00 00 ....
[ 10.724696] FIX kmalloc-rnd-05-32: Object at 0xffff9d9a80356600 not freed
Co-authored-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
---
Changes since v1:
https://lore.kernel.org/all/Zij_fGjRS_rK-65r@archlinux/
* Jump above out of object freepointer if init_on_free is set
instead of initializing it with set_freepointer() as suggested
by Vlastimil Babka.
* Adapt maybe_wipe_obj_freeptr() to avoid wiping out of object
on alloc freepointer as suggested by Chengming Zhou.
* Reword commit message.
---
mm/slub.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 3aa12b9b323d..173c340ec1d3 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2102,15 +2102,20 @@ bool slab_free_hook(struct kmem_cache *s, void *x, bool init)
*
* The initialization memset's clear the object and the metadata,
* but don't touch the SLAB redzone.
+ *
+ * The object's freepointer is also avoided if stored outside the
+ * object.
*/
if (unlikely(init)) {
int rsize;
+ unsigned int inuse;
+ inuse = get_info_end(s);
if (!kasan_has_integrated_init())
memset(kasan_reset_tag(x), 0, s->object_size);
rsize = (s->flags & SLAB_RED_ZONE) ? s->red_left_pad : 0;
- memset((char *)kasan_reset_tag(x) + s->inuse, 0,
- s->size - s->inuse - rsize);
+ memset((char *)kasan_reset_tag(x) + inuse, 0,
+ s->size - inuse - rsize);
}
/* KASAN might put x into memory quarantine, delaying its reuse. */
return !kasan_slab_free(s, x, init);
@@ -3789,7 +3794,7 @@ static void *__slab_alloc_node(struct kmem_cache *s,
static __always_inline void maybe_wipe_obj_freeptr(struct kmem_cache *s,
void *obj)
{
- if (unlikely(slab_want_init_on_free(s)) && obj)
+ if (unlikely(slab_want_init_on_free(s)) && obj && !freeptr_outside_object(s))
memset((void *)((char *)kasan_reset_tag(obj) + s->offset),
0, sizeof(void *));
}
--
2.44.0
