Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Qian Cai <cai@lca.pw>
To:     akpm@linux-foundation.org, cl@linux.com, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com
Cc:     andreyknvl@google.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Qian Cai <cai@lca.pw>
Subject: [PATCH] slub: untag object before slab end
Date:   Tue, 12 Feb 2019 21:05:50 -0500
Message-Id: <20190213020550.82453-1-cai@lca.pw>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@lca.pw>
---

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)