On Mon, Aug 1, 2016 at 4:45 PM, Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxxxxxxxxx>
> Reported-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> Reported-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Acked-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
> 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);
This is exactly the patch I was going to send in a couple of minutes :)
> return true;
> case KASAN_STATE_QUARANTINE:
> case KASAN_STATE_FREE:
> --
> 2.7.3
>
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
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