[PATCH 1/6] mm/kasan: fix corruptions and false positive reports

Andrey Ryabinin
2016-08-01T17:25:43Z

Once object put in quarantine, we no longer own it, i.e. object could leave
the quarantine and be reallocated. So having set_track() call after the
quarantine_put() may corrupt slab objects.

BUG kmalloc-4096 (Not tainted): Poison overwritten
-----------------------------------------------------------------------------
Disabling lock debugging due to kernel taint
INFO: 0xffff8804540de850-0xffff8804540de857. First byte 0xb5 instead of 0x6b
...
INFO: Freed in qlist_free_all+0x42/0x100 age=75 cpu=3 pid=24492
__slab_free+0x1d6/0x2e0
___cache_free+0xb6/0xd0
qlist_free_all+0x83/0x100
quarantine_reduce+0x177/0x1b0
kasan_kmalloc+0xf3/0x100
kasan_slab_alloc+0x12/0x20
kmem_cache_alloc+0x109/0x3e0
mmap_region+0x53e/0xe40
do_mmap+0x70f/0xa50
vm_mmap_pgoff+0x147/0x1b0
SyS_mmap_pgoff+0x2c7/0x5b0
SyS_mmap+0x1b/0x30
do_syscall_64+0x1a0/0x4e0
return_from_SYSCALL_64+0x0/0x7a
INFO: Slab 0xffffea0011503600 objects=7 used=7 fp=0x (null) flags=0x8000000000004080
INFO: Object 0xffff8804540de848 @offset=26696 fp=0xffff8804540dc588
Redzone ffff8804540de840: bb bb bb bb bb bb bb bb ........
Object ffff8804540de848: 6b 6b 6b 6b 6b 6b 6b 6b b5 52 00 00 f2 01 60 cc kkkkkkkk.R....`.

Similarly, poisoning after the quarantine_put() leads to false positive
use-after-free reports:

BUG: KASAN: use-after-free in anon_vma_interval_tree_insert+0x304/0x430 at addr ffff880405c540a0
Read of size 8 by task trinity-c0/3036
CPU: 0 PID: 3036 Comm: trinity-c0 Not tainted 4.7.0-think+ #9
ffff880405c54200 00000000c5c4423e ffff88044a5ef9f0 ffffffffaea48532
ffff88044a5efa88 ffff880461497a00 ffff88044a5efa78 ffffffffae57cfe2
ffff88046501c958 ffff880436aa5440 0000000000000282 0000000000000007
Call Trace:
[<ffffffffaea48532>] dump_stack+0x68/0x96
[<ffffffffae57cfe2>] kasan_report_error+0x222/0x600
[<ffffffffae57d571>] __asan_report_load8_noabort+0x61/0x70
[<ffffffffae4f8924>] anon_vma_interval_tree_insert+0x304/0x430
[<ffffffffae52f811>] anon_vma_chain_link+0x91/0xd0
[<ffffffffae536e46>] anon_vma_clone+0x136/0x3f0
[<ffffffffae537181>] anon_vma_fork+0x81/0x4c0
[<ffffffffae125663>] copy_process.part.47+0x2c43/0x5b20
[<ffffffffae12895d>] _do_fork+0x16d/0xbd0
[<ffffffffae129469>] SyS_clone+0x19/0x20
[<ffffffffae0064b0>] do_syscall_64+0x1a0/0x4e0
[<ffffffffafa09b1a>] entry_SYSCALL64_slow_path+0x25/0x25

Fix this by putting an object in the quarantine after all other operations.

Fixes: 80a9201a5965 ("mm, kasan: switch SLUB to stackdepot, enable memory quarantine for SLUB")
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Reported-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
mm/kasan/kasan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index b6f99e8..3019cec 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -543,9 +543,9 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)
switch (alloc_info->state) {
case KASAN_STATE_ALLOC:
alloc_info->state = KASAN_STATE_QUARANTINE;
- quarantine_put(free_info, cache);
set_track(&free_info->track, GFP_NOWAIT);
kasan_poison_slab_free(cache, object);
+ quarantine_put(free_info, cache);
return true;
case KASAN_STATE_QUARANTINE:
case KASAN_STATE_FREE:
--
2.7.3