Re: KASAN: use-after-free in membarrier_mm_sync_core_before_usermode

[Mathieu Desnoyers]

----- On Nov 15, 2017, at 5:44 AM, Dmitry Vyukov dvyukov@xxxxxxxxxx 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.

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