Re: usercopy whitelist woe in scsi_sense_cache

[Kees Cook]

On Thu, Apr 12, 2018 at 8:02 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Thu, Apr 12, 2018 at 3:47 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> After fixing up some build issues in the middle of the 4.16 cycle, I
>> get an unhelpful bisect result of commit 0a4b6e2f80aa ("Merge branch
>> 'for-4.16/block'"). Instead of letting the test run longer, I'm going
>> to switch to doing several shorter test boots per kernel and see if
>> that helps. One more bisect coming...
>
> Okay, so I can confirm the bisect points at the _merge_ itself, not a
> specific patch. I'm not sure how to proceed here. It looks like some
> kind of interaction between separate trees? Jens, do you have
> suggestions on how to track this down?

Turning off HARDENED_USERCOPY and turning on KASAN, I see the same report:

[   38.274106] BUG: KASAN: slab-out-of-bounds in _copy_to_user+0x42/0x60
[   38.274841] Read of size 22 at addr ffff8800122b8c4b by task smartctl/1064
[   38.275630]
[   38.275818] CPU: 2 PID: 1064 Comm: smartctl Not tainted 4.17.0-rc1-ARCH+ #266
[   38.276631] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[   38.277690] Call Trace:
[   38.277988]  dump_stack+0x71/0xab
[   38.278397]  ? _copy_to_user+0x42/0x60
[   38.278833]  print_address_description+0x6a/0x270
[   38.279368]  ? _copy_to_user+0x42/0x60
[   38.279800]  kasan_report+0x243/0x360
[   38.280221]  _copy_to_user+0x42/0x60
[   38.280635]  sg_io+0x459/0x660
...

Though we get slightly more details (some we already knew):

[   38.301330] Allocated by task 329:
[   38.301734]  kmem_cache_alloc_node+0xca/0x220
[   38.302239]  scsi_mq_init_request+0x64/0x130 [scsi_mod]
[   38.302821]  blk_mq_alloc_rqs+0x2cf/0x370
[   38.303265]  blk_mq_sched_alloc_tags.isra.4+0x7d/0xb0
[   38.303820]  blk_mq_init_sched+0xf0/0x220
[   38.304268]  elevator_switch+0x17a/0x2c0
[   38.304705]  elv_iosched_store+0x173/0x220
[   38.305171]  queue_attr_store+0x72/0xb0
[   38.305602]  kernfs_fop_write+0x188/0x220
[   38.306049]  __vfs_write+0xb6/0x330
[   38.306436]  vfs_write+0xe9/0x240
[   38.306804]  ksys_write+0x98/0x110
[   38.307181]  do_syscall_64+0x6d/0x1d0
[   38.307590]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   38.308142]
[   38.308316] Freed by task 0:
[   38.308652] (stack is not available)
[   38.309060]
[   38.309243] The buggy address belongs to the object at ffff8800122b8c00
[   38.309243]  which belongs to the cache scsi_sense_cache of size 96
[   38.310625] The buggy address is located 75 bytes inside of
[   38.310625]  96-byte region [ffff8800122b8c00, ffff8800122b8c60)


-Kees

-- 
Kees Cook
Pixel Security