linux-kernel - [PATCH] slab: store tagged freelist for off-slab slabmgmt

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Date:   Tue,  2 Apr 2019 22:28:58 -0400
From:   Qian Cai <cai@....pw>
To:     akpm@...ux-foundation.org
Cc:     andreyknvl@...gle.com, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        aryabinin@...tuozzo.com, glider@...gle.com, dvyukov@...gle.com,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Qian Cai <cai@....pw>
Subject: [PATCH] slab: store tagged freelist for off-slab slabmgmt

The commit 51dedad06b5f ("kasan, slab: make freelist stored without
tags") calls kasan_reset_tag() for off-slab slab management object
leading to freelist being stored non-tagged. However, cache_grow_begin()
-> alloc_slabmgmt() -> kmem_cache_alloc_node() which assigns a tag for
the address and stores in the shadow address. As the result, it causes
endless errors below during boot due to drain_freelist() ->
slab_destroy() -> kasan_slab_free() which compares already untagged
freelist against the stored tag in the shadow address. Since off-slab
slab management object freelist is such a special case, so just store it
tagged. Non-off-slab management object freelist is still stored untagged
which has not been assigned a tag and should not cause any other
troubles with this inconsistency.

BUG: KASAN: double-free or invalid-free in slab_destroy+0x84/0x88
Pointer tag: [ff], memory tag: [99]

CPU: 0 PID: 1376 Comm: kworker/0:4 Tainted: G        W
5.1.0-rc3+ #8
Hardware name: HPE Apollo 70             /C01_APACHE_MB         , BIOS
L50_5.13_1.0.6 07/10/2018
Workqueue: cgroup_destroy css_killed_work_fn
Call trace:
 dump_backtrace+0x0/0x450
 show_stack+0x20/0x2c
 dump_stack+0xe0/0x16c
 print_address_description+0x74/0x2a4
 kasan_report_invalid_free+0x80/0xc0
 __kasan_slab_free+0x204/0x208
 kasan_slab_free+0xc/0x18
 kmem_cache_free+0xe4/0x254
 slab_destroy+0x84/0x88
 drain_freelist+0xd0/0x104
 __kmem_cache_shrink+0x1ac/0x224
 __kmemcg_cache_deactivate+0x1c/0x28
 memcg_deactivate_kmem_caches+0xa0/0xe8
 memcg_offline_kmem+0x8c/0x3d4
 mem_cgroup_css_offline+0x24c/0x290
 css_killed_work_fn+0x154/0x618
 process_one_work+0x9cc/0x183c
 worker_thread+0x9b0/0xe38
 kthread+0x374/0x390
 ret_from_fork+0x10/0x18

Allocated by task 1625:
 __kasan_kmalloc+0x168/0x240
 kasan_slab_alloc+0x18/0x20
 kmem_cache_alloc_node+0x1f8/0x3a0
 cache_grow_begin+0x4fc/0xa24
 cache_alloc_refill+0x2f8/0x3e8
 kmem_cache_alloc+0x1bc/0x3bc
 sock_alloc_inode+0x58/0x334
 alloc_inode+0xb8/0x164
 new_inode_pseudo+0x20/0xec
 sock_alloc+0x74/0x284
 __sock_create+0xb0/0x58c
 sock_create+0x98/0xb8
 __sys_socket+0x60/0x138
 __arm64_sys_socket+0xa4/0x110
 el0_svc_handler+0x2c0/0x47c
 el0_svc+0x8/0xc

Freed by task 1625:
 __kasan_slab_free+0x114/0x208
 kasan_slab_free+0xc/0x18
 kfree+0x1a8/0x1e0
 single_release+0x7c/0x9c
 close_pdeo+0x13c/0x43c
 proc_reg_release+0xec/0x108
 __fput+0x2f8/0x784
 ____fput+0x1c/0x28
 task_work_run+0xc0/0x1b0
 do_notify_resume+0xb44/0x1278
 work_pending+0x8/0x10

The buggy address belongs to the object at ffff809681b89e00
 which belongs to the cache kmalloc-128 of size 128
The buggy address is located 0 bytes inside of
 128-byte region [ffff809681b89e00, ffff809681b89e80)
The buggy address belongs to the page:
page:ffff7fe025a06e00 count:1 mapcount:0 mapping:01ff80082000fb00
index:0xffff809681b8fe04
flags: 0x17ffffffc000200(slab)
raw: 017ffffffc000200 ffff7fe025a06d08 ffff7fe022ef7b88 01ff80082000fb00
raw: ffff809681b8fe04 ffff809681b80000 00000001000000e0 0000000000000000
page dumped because: kasan: bad access detected
page allocated via order 0, migratetype Unmovable, gfp_mask
0x2420c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_COMP|__GFP_THISNODE)
 prep_new_page+0x4e0/0x5e0
 get_page_from_freelist+0x4ce8/0x50d4
 __alloc_pages_nodemask+0x738/0x38b8
 cache_grow_begin+0xd8/0xa24
 ____cache_alloc_node+0x14c/0x268
 __kmalloc+0x1c8/0x3fc
 ftrace_free_mem+0x408/0x1284
 ftrace_free_init_mem+0x20/0x28
 kernel_init+0x24/0x548
 ret_from_fork+0x10/0x18

Memory state around the buggy address:
 ffff809681b89c00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
 ffff809681b89d00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
>ffff809681b89e00: 99 99 99 99 99 99 99 99 fe fe fe fe fe fe fe fe
                   ^
 ffff809681b89f00: 43 43 43 43 43 fe fe fe fe fe fe fe fe fe fe fe
 ffff809681b8a000: 6d fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe

Fixes: 51dedad06b5f ("kasan, slab: make freelist stored without tags")
Signed-off-by: Qian Cai <cai@....pw>
---
 mm/slab.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index 329bfe67f2ca..46a6e084222b 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2374,7 +2374,6 @@ static void *alloc_slabmgmt(struct kmem_cache *cachep,
 		/* Slab management obj is off-slab. */
 		freelist = kmem_cache_alloc_node(cachep->freelist_cache,
 					      local_flags, nodeid);
-		freelist = kasan_reset_tag(freelist);
 		if (!freelist)
 			return NULL;
 	} else {
-- 
2.17.2 (Apple Git-113)