[PATCH] slub: untag object before slab end
From: Qian Cai
Date: Tue Feb 12 2019 - 21:06:06 EST
get_freepointer() could return NULL if there is no more free objects in
the slab. However, it could return a tagged pointer (like
0x2200000000000000) with KASAN_SW_TAGS which would escape the NULL
object checking in check_valid_pointer() and trigger errors below, so
untag the object before checking for a NULL object there.
[ 35.797667] BUG kmalloc-256 (Not tainted): Freepointer corrupt
[ 35.803584] -----------------------------------------------------------------------------
[ 35.803584]
[ 35.813368] Disabling lock debugging due to kernel taint
[ 35.818766] INFO: Allocated in build_sched_domains+0x28c/0x495c age=92 cpu=0 pid=1
[ 35.826443] __kmalloc_node+0x4ac/0x508
[ 35.830343] build_sched_domains+0x28c/0x495c
[ 35.834764] sched_init_domains+0x184/0x1d8
[ 35.839012] sched_init_smp+0x38/0xd4
[ 35.842732] kernel_init_freeable+0x67c/0x1104
[ 35.847243] kernel_init+0x18/0x2a4
[ 35.850790] ret_from_fork+0x10/0x18
[ 35.854423] INFO: Freed in destroy_sched_domain+0xa0/0xcc age=11 cpu=0 pid=1
[ 35.861569] destroy_sched_domain+0xa0/0xcc
[ 35.865814] cpu_attach_domain+0x304/0xb34
[ 35.869971] build_sched_domains+0x4654/0x495c
[ 35.874480] sched_init_domains+0x184/0x1d8
[ 35.878724] sched_init_smp+0x38/0xd4
[ 35.882443] kernel_init_freeable+0x67c/0x1104
[ 35.886953] kernel_init+0x18/0x2a4
[ 35.890495] ret_from_fork+0x10/0x18
[ 35.894128] INFO: Slab 0x(____ptrval____) objects=85 used=0 fp=0x(____ptrval____) flags=0x7ffffffc000200
[ 35.903733] INFO: Object 0x(____ptrval____) @offset=38528 fp=0x(____ptrval____)
[ 35.903733]
[ 35.912637] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 35.922155] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 35.931672] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 35.941190] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 35.950707] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 35.960224] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 35.969741] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 35.979258] Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 35.988776] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 35.998206] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.007636] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.017065] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.026494] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.035923] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.045353] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.054783] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.064212] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.073642] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.083071] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.092501] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.101930] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.111359] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.120788] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
[ 36.130218] Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk.
[ 36.139647] Redzone (____ptrval____): bb bb bb bb bb bb bb bb ........
[ 36.148462] Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
[ 36.157979] Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
[ 36.167496] Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
[ 36.177021] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G B 5.0.0-rc6+ #41
[ 36.184854] Call trace:
[ 36.187328] dump_backtrace+0x0/0x450
[ 36.191032] show_stack+0x20/0x2c
[ 36.194385] __dump_stack+0x20/0x28
[ 36.197911] dump_stack+0xa0/0xfc
[ 36.201265] print_trailer+0x1a8/0x1bc
[ 36.205057] object_err+0x40/0x50
[ 36.208408] check_object+0x214/0x2b8
[ 36.212111] __free_slab+0x9c/0x31c
[ 36.215638] discard_slab+0x78/0xa8
[ 36.219165] kfree+0x918/0x980
[ 36.222259] destroy_sched_domain+0xa0/0xcc
[ 36.226489] cpu_attach_domain+0x304/0xb34
[ 36.230631] build_sched_domains+0x4654/0x495c
[ 36.235125] sched_init_domains+0x184/0x1d8
[ 36.239357] sched_init_smp+0x38/0xd4
[ 36.243060] kernel_init_freeable+0x67c/0x1104
[ 36.247555] kernel_init+0x18/0x2a4
[ 36.251083] ret_from_fork+0x10/0x18
Signed-off-by: Qian Cai <cai@xxxxxx>
---
Depends on slub-fix-slab_consistency_checks-kasan_sw_tags.patch.
mm/slub.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/slub.c b/mm/slub.c
index 4a61959e1887..2fd1cf39914c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -503,11 +503,11 @@ static inline int check_valid_pointer(struct kmem_cache *s,
{
void *base;
+ object = kasan_reset_tag(object);
if (!object)
return 1;
base = page_address(page);
- object = kasan_reset_tag(object);
object = restore_red_left(s, object);
if (object < base || object >= base + page->objects * s->size ||
(object - base) % s->size) {
--
2.17.2 (Apple Git-113)