Re: [PATCH v4] mm, kasan: switch SLUB to stackdepot, enable memory quarantine for SLUB

[Alexander Potapenko]

On Sat, Jun 18, 2016 at 5:32 PM, Sasha Levin <sasha.levin@xxxxxxxxxx> wrote:
> On 06/17/2016 10:27 AM, Alexander Potapenko wrote:
>> For KASAN builds:
>>  - switch SLUB allocator to using stackdepot instead of storing the
>>    allocation/deallocation stacks in the objects;
>>  - define SLAB_RED_ZONE, SLAB_POISON, SLAB_STORE_USER to zero,
>>    effectively disabling these debug features, as they're redundant in
>>    the presence of KASAN;
>>  - change the freelist hook so that parts of the freelist can be put into
>>    the quarantine.
>>
>> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
>
> Hi Alexander,
>
> I was seeing a bunch of use-after-frees detected by kasan, such as:
>
> BUG: KASAN: use-after-free in rb_next+0x117/0x1b0 at addr ffff8800b01d4f30
> Read of size 8 by task syz-executor/31594
> CPU: 2 PID: 31594 Comm: syz-executor Tainted: G        W       4.7.0-rc2-sasha-00205-g2d8a14b #3117
>  1ffff10015450f0f 000000007b9351fc ffff8800aa287900 ffffffffa002778b
>  ffffffff00000002 fffffbfff5630d30 0000000041b58ab3 ffffffffaaad5648
>  ffffffffa002761c ffffffff9e006ab6 ffffffffa8439f65 ffffffffffffffff
> Call Trace:
>  [<ffffffffa002778b>] dump_stack+0x16f/0x1d4
>  [<ffffffff9e79e8cf>] kasan_report_error+0x59f/0x8c0
>  [<ffffffff9e79ee06>] __asan_report_load8_noabort+0x66/0x90
>  [<ffffffffa003ccf7>] rb_next+0x117/0x1b0
>  [<ffffffff9e71627c>] validate_mm_rb+0xac/0xd0
>  [<ffffffff9e718594>] __vma_link_rb+0x2e4/0x310
>  [<ffffffff9e718650>] vma_link+0x90/0x1b0
>  [<ffffffff9e722870>] mmap_region+0x13a0/0x13c0
>  [<ffffffff9e7232b2>] do_mmap+0xa22/0xaf0
>  [<ffffffff9e6c86bf>] vm_mmap_pgoff+0x14f/0x1c0
>  [<ffffffff9e71ba8b>] SyS_mmap_pgoff+0x81b/0x910
>  [<ffffffff9e1bf966>] SyS_mmap+0x16/0x20
>  [<ffffffff9e006ab6>] do_syscall_64+0x2a6/0x490
>  [<ffffffffa8439f65>] entry_SYSCALL64_slow_path+0x25/0x25
> Object at ffff8800b01d4f00, in cache vm_area_struct
> Object allocated with size 192 bytes.
> Allocation:
> PID = 8855
> (stack is not available)
> Memory state around the buggy address:
>  ffff8800b01d4e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8800b01d4e80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>>ffff8800b01d4f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                      ^
>  ffff8800b01d4f80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff8800b01d5000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>
> Or:
>
> BUG: KASAN: use-after-free in validate_mm_rb+0x73/0xd0 at addr ffff8800b01d4f38
> Read of size 8 by task syz-executor/31594
> CPU: 2 PID: 31594 Comm: syz-executor Tainted: G    B   W       4.7.0-rc2-sasha-00205-g2d8a14b #3117
>  1ffff10015450f16 000000007b9351fc ffff8800aa287938 ffffffffa002778b
>  ffffffff00000002 fffffbfff5630d30 0000000041b58ab3 ffffffffaaad5648
>  ffffffffa002761c ffffffffa84399e8 0000000000000010 ffff8800b61e8000
> Call Trace:
>  [<ffffffffa002778b>] dump_stack+0x16f/0x1d4
>  [<ffffffff9e79e8cf>] kasan_report_error+0x59f/0x8c0
>  [<ffffffff9e79ee06>] __asan_report_load8_noabort+0x66/0x90
>  [<ffffffff9e716243>] validate_mm_rb+0x73/0xd0
>  [<ffffffff9e718594>] __vma_link_rb+0x2e4/0x310
>  [<ffffffff9e718650>] vma_link+0x90/0x1b0
>  [<ffffffff9e722870>] mmap_region+0x13a0/0x13c0
>  [<ffffffff9e7232b2>] do_mmap+0xa22/0xaf0
>  [<ffffffff9e6c86bf>] vm_mmap_pgoff+0x14f/0x1c0
>  [<ffffffff9e71ba8b>] SyS_mmap_pgoff+0x81b/0x910
>  [<ffffffff9e1bf966>] SyS_mmap+0x16/0x20
>  [<ffffffff9e006ab6>] do_syscall_64+0x2a6/0x490
>  [<ffffffffa8439f65>] entry_SYSCALL64_slow_path+0x25/0x25
> Object at ffff8800b01d4f00, in cache vm_area_struct
> Object allocated with size 192 bytes.
> Allocation:
> PID = 8855
> (stack is not available)
> Memory state around the buggy address:
>  ffff8800b01d4e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8800b01d4e80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>>ffff8800b01d4f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                         ^
>  ffff8800b01d4f80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff8800b01d5000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>
> And bisection pointed me to this commit. Now, I'm not sure how to
> tell if this is memory quarantine catching something, or is just a
> bug with the patch?
>
>
> Thanks,
> Sasha

Hi Sasha,

This commit delays the reuse of memory after it has been freed, so
it's intended to help people find more use-after-free errors.
But I'm puzzled why the stacks are missing.
Can you please share the reproduction steps for this bug?
I also wonder whether it's reproducible when you:
 - revert this commit?
 - build with SLAB instead of SLUB?

HTH,
Alex

-- 
Alexander Potapenko
Software Engineer

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