Re: KASAN: use-after-free in membarrier_mm_sync_core_before_usermode

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On Nov 15, 2017, at 8:05 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:

> ----- On Nov 15, 2017, at 5:44 AM, Dmitry Vyukov dvyukov@google.com wrote:
> 
>> Hello,
>> 
>> I've tried to run latest linux-next on:
>> 
>> commit 63fb091c80188ec51f53514d07de907c1dd3d61d
>> Author: Stephen Rothwell <sfr@...>
>> Date:   Wed Nov 15 16:44:31 2017 +1100
>>    Add linux-next specific files for 20171115
>> 
>> and it crashes during boot with:
> 
> The line:
> 
> membarrier_mm_sync_core_before_usermode(mm);
> 
> should be
> 
> membarrier_mm_sync_core_before_usermode(current->mm);
> 
> Given that we want to check the flags on the next mm at this point.
> 
> I'll run this through KASAN and update the patchset.

Actually "mm" is prev_mm and is the right mm. I just needed
to move this call before mmdrop(mm). I'm currently booting and
running the selftests with kasan enabled and it works fine now.
I'll update the patch.

Thanks!

Mathieu



> 
> Thanks!
> 
> Mathieu
> 
> 
>> 
>> ==================================================================
>> BUG: KASAN: use-after-free in __read_once_size
>> include/linux/compiler.h:183 [inline]
>> BUG: KASAN: use-after-free in atomic_read
>> arch/x86/include/asm/atomic.h:27 [inline]
>> BUG: KASAN: use-after-free in membarrier_mm_sync_core_before_usermode
>> include/linux/sched/mm.h:216 [inline]
>> BUG: KASAN: use-after-free in finish_task_switch+0x61f/0x7c0
>> kernel/sched/core.c:2712
>> Read of size 4 at addr ffff880064fe5170 by task rc/1535
>> 
>> CPU: 0 PID: 1535 Comm: rc Not tainted 4.14.0-next-20171115 #22
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> Call Trace:
>> __dump_stack lib/dump_stack.c:17 [inline]
>> dump_stack+0x194/0x257 lib/dump_stack.c:53
>> print_address_description+0x73/0x250 mm/kasan/report.c:252
>> kasan_report_error mm/kasan/report.c:351 [inline]
>> kasan_report+0x25b/0x340 mm/kasan/report.c:409
>> __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
>> __read_once_size include/linux/compiler.h:183 [inline]
>> atomic_read arch/x86/include/asm/atomic.h:27 [inline]
>> membarrier_mm_sync_core_before_usermode include/linux/sched/mm.h:216 [inline]
>> finish_task_switch+0x61f/0x7c0 kernel/sched/core.c:2712
>> schedule_tail+0xe/0x100 kernel/sched/core.c:2789
>> ret_from_fork+0x8/0x30 arch/x86/entry/entry_64.S:422
>> RIP: 0033:0x7fee2a8fdf46
>> RSP: 002b:00007ffddfd435b0 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
>> RAX: 0000000000000000 RBX: 00007ffddfd435b0 RCX: 00007fee2a8fdf46
>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
>> RBP: 00007ffddfd435f0 R08: 0000000000000000 R09: 00000000000005fc
>> R10: 00007fee2adf59d0 R11: 0000000000000246 R12: 0000000000000000
>> R13: 0000000000000000 R14: 0000000000415d62 R15: 0000000000000001
>> 
>> Allocated by task 1532:
>> save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>> set_track mm/kasan/kasan.c:459 [inline]
>> kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
>> kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
>> kmem_cache_alloc+0x12e/0x760 mm/slab.c:3548
>> dup_mm kernel/fork.c:1230 [inline]
>> copy_mm+0x30a/0x1310 kernel/fork.c:1293
>> copy_process.part.36+0x1f31/0x4d70 kernel/fork.c:1797
>> copy_process kernel/fork.c:1610 [inline]
>> _do_fork+0x1ef/0xff0 kernel/fork.c:2091
>> SYSC_clone kernel/fork.c:2201 [inline]
>> SyS_clone+0x37/0x50 kernel/fork.c:2195
>> do_syscall_64+0x26c/0x920 arch/x86/entry/common.c:286
>> return_from_SYSCALL_64+0x0/0x75
>> 
>> Freed by task 1535:
>> save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>> set_track mm/kasan/kasan.c:459 [inline]
>> kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
>> __cache_free mm/slab.c:3492 [inline]
>> kmem_cache_free+0x77/0x280 mm/slab.c:3750
>> __mmdrop+0x242/0x3d0 kernel/fork.c:604
>> mmdrop+0x28/0x30 kernel/fork.c:610
>> finish_task_switch+0x204/0x7c0 kernel/sched/core.c:2711
>> schedule_tail+0xe/0x100 kernel/sched/core.c:2789
>> ret_from_fork+0x8/0x30 arch/x86/entry/entry_64.S:422
>> 
>> The buggy address belongs to the object at ffff880064fe4d00
>> which belongs to the cache mm_struct of size 1368
>> The buggy address is located 1136 bytes inside of
>> 1368-byte region [ffff880064fe4d00, ffff880064fe5258)
>> The buggy address belongs to the page:
>> page:ffffea000193f900 count:1 mapcount:0 mapping:ffff880064fe4100
>> index:0x0 compound_mapcount: 0
>> flags: 0x1fffc0000008100(slab|head)
>> raw: 01fffc0000008100 ffff880064fe4100 0000000000000000 0000000100000005
>> raw: ffffea000193eba0 ffff88006c9f8f50 ffff88006c9f7b40 0000000000000000
>> page dumped because: kasan: bad access detected
>> 
>> Memory state around the buggy address:
>> ffff880064fe5000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff880064fe5080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>ffff880064fe5100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>                                                             ^
>> ffff880064fe5180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff880064fe5200: fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc
>> ==================================================================
> 
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com