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mm/slub: avoid zeroing outside-object freepointer for single free 

Commit 284f17ac13 ("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().

During bulk free, slab_free_freelist_hook() isn't affected as it always
sets it objects freepointer using set_freepointer() to maintain its
reconstructed freelist after `init_on_free`.

For single free, object's freepointer thus needs to be avoided when
stored outside the object if `init_on_free` is set. The freepointer left
as is, check_object() may later detect an invalid pointer value due to
objects overflow.

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

Fixes: 284f17ac13 ("mm/slub: handle bulk and single object freeing separately")
Cc: <stable@vger.kernel.org>
Co-developed-by: Chengming Zhou <chengming.zhou@linux.dev>
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
This commit is contained in:
Nicolas Bouchinet 2024-04-30 13:34:59 +02:00 committed by Vlastimil Babka
parent e67572cd22
commit 8f828aa488
1 changed files with 29 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
mm/slub.c
View File

@ -557,6 +557,26 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
*(freeptr_t *)freeptr_addr = freelist_ptr_encode(s, fp, freeptr_addr);
}
/*
* See comment in calculate_sizes().
*/
static inline bool freeptr_outside_object(struct kmem_cache *s)
{
return s->offset >= s->inuse;
}
/*
* Return offset of the end of info block which is inuse + free pointer if
* not overlapping with object.
*/
static inline unsigned int get_info_end(struct kmem_cache *s)
{
if (freeptr_outside_object(s))
return s->inuse + sizeof(void *);
else
return s->inuse;
}
/* Loop over all objects in a slab */
#define for_each_object(__p, __s, __addr, __objects) \
for (__p = fixup_red_left(__s, __addr); \
@ -845,26 +865,6 @@ static void print_section(char *level, char *text, u8 *addr,
metadata_access_disable();
}
/*
* See comment in calculate_sizes().
*/
static inline bool freeptr_outside_object(struct kmem_cache *s)
{
return s->offset >= s->inuse;
}
/*
* Return offset of the end of info block which is inuse + free pointer if
* not overlapping with object.
*/
static inline unsigned int get_info_end(struct kmem_cache *s)
{
if (freeptr_outside_object(s))
return s->inuse + sizeof(void *);
else
return s->inuse;
}
static struct track *get_track(struct kmem_cache *s, void *object,
enum track_item alloc)
{
@ -2092,15 +2092,20 @@ 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);
@ -3722,7 +3727,8 @@ 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 *));
}