Re: KASAN: use-after-free Read in __do_page_fault

From: Vlastimil Babka
Date: Tue Oct 31 2017 - 09:58:05 EST

Next message: Dmitry Vyukov: "Re: general protection fault in gfn_to_rmap"
Previous message: Roger Quadros: "[PATCH v2][RESEND] usb: gadget: core: Fix ->udc_set_speed() speed handling"
In reply to: Vlastimil Babka: "Re: KASAN: use-after-free Read in __do_page_fault"
Next in thread: Kirill A. Shutemov: "Re: KASAN: use-after-free Read in __do_page_fault"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

+CC Andrea, Thorsten, Linus

On 10/31/2017 02:20 PM, Vlastimil Babka wrote:
> On 10/31/2017 01:42 PM, Dmitry Vyukov wrote:
>>> My vm_area_struct is 192 bytes, could be your layout is different due to
>>> .config. At offset 80 I have vma->vm_flags. That is checked by
>>> __do_page_fault(), but only after vma->vm_start (offset 0). Of course,
>>> reordering is possible.
>>
>>
>> It seems that compiler over-optimizes things and messes debug info.
>> I just re-reproduced this on upstream
>> 15f859ae5c43c7f0a064ed92d33f7a5bc5de6de0 and got the same report:
>>
>> ==================================================================
>> BUG: KASAN: use-after-free in arch_local_irq_enable
>> arch/x86/include/asm/paravirt.h:787 [inline]
>> BUG: KASAN: use-after-free in __do_page_fault+0xc03/0xd60
>> arch/x86/mm/fault.c:1357
>> Read of size 8 at addr ffff880064d19aa0 by task syz-executor/8001
>>
>> CPU: 0 PID: 8001 Comm: syz-executor Not tainted 4.14.0-rc6+ #12
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> Call Trace:
>> __dump_stack lib/dump_stack.c:16 [inline]
>> dump_stack+0x194/0x257 lib/dump_stack.c:52
>> 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_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>> arch_local_irq_enable arch/x86/include/asm/paravirt.h:787 [inline]
>> __do_page_fault+0xc03/0xd60 arch/x86/mm/fault.c:1357
>> do_page_fault+0xee/0x720 arch/x86/mm/fault.c:1520
>> do_async_page_fault+0x82/0x110 arch/x86/kernel/kvm.c:273
>> async_page_fault+0x22/0x30 arch/x86/entry/entry_64.S:1069
>> RIP: 0033:0x441bd0
>> RSP: 002b:00007f2ed8229798 EFLAGS: 00010202
>> RAX: 00007f2ed82297c0 RBX: 0000000000000000 RCX: 000000000000000e
>> RDX: 0000000000000400 RSI: 0000000020012fe0 RDI: 00007f2ed82297c0
>> RBP: 0000000000748020 R08: 0000000000000400 R09: 0000000000000000
>> R10: 0000000020012fee R11: 0000000000000246 R12: 00000000ffffffff
>> R13: 0000000000008430 R14: 00000000006ec4d0 R15: 00007f2ed822a700
>>
>> Allocated by task 8001:
>> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
>> 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:3561
>> kmem_cache_zalloc include/linux/slab.h:656 [inline]
>> mmap_region+0x7ee/0x15a0 mm/mmap.c:1658
>> do_mmap+0x69b/0xd40 mm/mmap.c:1468
>> do_mmap_pgoff include/linux/mm.h:2150 [inline]
>> vm_mmap_pgoff+0x1de/0x280 mm/util.c:333
>> SYSC_mmap_pgoff mm/mmap.c:1518 [inline]
>> SyS_mmap_pgoff+0x23b/0x5f0 mm/mmap.c:1476
>> SYSC_mmap arch/x86/kernel/sys_x86_64.c:99 [inline]
>> SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:90
>> entry_SYSCALL_64_fastpath+0x1f/0xbe
>>
>> Freed by task 8007:
>> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
>> 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:3503 [inline]
>> kmem_cache_free+0x77/0x280 mm/slab.c:3763
>> remove_vma+0x162/0x1b0 mm/mmap.c:176
>> remove_vma_list mm/mmap.c:2475 [inline]
>> do_munmap+0x82a/0xdf0 mm/mmap.c:2714
>> mmap_region+0x59e/0x15a0 mm/mmap.c:1631
>> do_mmap+0x69b/0xd40 mm/mmap.c:1468
>> do_mmap_pgoff include/linux/mm.h:2150 [inline]
>> vm_mmap_pgoff+0x1de/0x280 mm/util.c:333
>> SYSC_mmap_pgoff mm/mmap.c:1518 [inline]
>> SyS_mmap_pgoff+0x23b/0x5f0 mm/mmap.c:1476
>> SYSC_mmap arch/x86/kernel/sys_x86_64.c:99 [inline]
>> SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:90
>> entry_SYSCALL_64_fastpath+0x1f/0xbe
>>
>> The buggy address belongs to the object at ffff880064d19a50
>> which belongs to the cache vm_area_struct of size 200
>> The buggy address is located 80 bytes inside of
>> 200-byte region [ffff880064d19a50, ffff880064d19b18)
>> The buggy address belongs to the page:
>> page:ffffea0001934640 count:1 mapcount:0 mapping:ffff880064d19000 index:0x0
>> flags: 0x100000000000100(slab)
>> raw: 0100000000000100 ffff880064d19000 0000000000000000 000000010000000f
>> raw: ffffea00018a3a60 ffffea0001940be0 ffff88006c5f79c0 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>> ffff880064d19980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff880064d19a00: fb fb fc fc fc fc fc fc fc fc fb fb fb fb fb fb
>>> ffff880064d19a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ^
>> ffff880064d19b00: fb fb fb fc fc fc fc fc fc fc fc fb fb fb fb fb
>> ffff880064d19b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ==================================================================
>>
>>
>> Here is disasm of the function:
>> https://gist.githubusercontent.com/dvyukov/5a56c66ce605168c951a321d94df6e3a/raw/538d4ce72ceb5631dfcc866ccde46c74543de1cf/gistfile1.txt
>>
>> Seems to be vma->vm_flags at offset 80.
>
> You can see it from the disasm? I can't make much of it, unfortunately,
> the added kasan calls obscure it a lot for me. But I suspect it might be
> the vma_pkey() thing which reads from vma->vm_flags. What happens when
> CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS is disabled? (or is it already?)

OK, so I opened the google groups link in the report's signature and
looked at the attached config there, which says protkeys are enabled.
Also looked at the repro.txt attachment:
#{Threaded:true Collide:true Repeat:true Procs:8 Sandbox:none Fault:false FaultCall:-1 FaultNth:0 EnableTun:true UseTmpDir:true HandleSegv:true WaitRepeat:true Debug:false Repro:false}
mmap(&(0x7f0000000000/0xfff000)=nil, 0xfff000, 0x3, 0x32, 0xffffffffffffffff, 0x0)
mmap(&(0x7f0000011000/0x3000)=nil, 0x3000, 0x1, 0x32, 0xffffffffffffffff, 0x0)
r0 = userfaultfd(0x0)
ioctl$UFFDIO_API(r0, 0xc018aa3f, &(0x7f0000002000-0x18)={0xaa, 0x0, 0x0})
ioctl$UFFDIO_REGISTER(r0, 0xc020aa00, &(0x7f0000019000)={{&(0x7f0000012000/0x2000)=nil, 0x2000}, 0x1, 0x0})
r1 = gettid()
syz_open_dev$evdev(&(0x7f0000013000-0x12)="2f6465762f696e7075742f6576656e742300", 0x0, 0x0)
tkill(r1, 0x7)

The userfaultfd() caught my attention so I checked handle_userfault()
which seems to do up_read(&mm->mmap_sem); and in some cases later
followed by down_read(&mm->mmap_sem); return VM_FAULT_NOPAGE.
However, __do_page_fault() only expects that mmap_sem to be released
when handle_mm_fault() returns with VM_FAULT_RETRY. It doesn't expect it
to be released and then acquired again, because then vma can be indeed
gone. It seems vma hasn't been touched after that point until the
vma_pkey() was added by commit a3c4fb7c9c2e ("x86/mm: Fix fault error
path using unsafe vma pointer") in rc3. Which tried to fix a similar
problem, but run into this corner case?

So I suspect a3c4fb7c9c2e is the culprit and thus a regression.

> Also did you try the vmacache shortcut test suggested in my previous mail?
>
>> I think the size of 200 reported by slab is OK as it can do some rounding.
>> Everything points to a vma object.
>>
>>
>>>>> The buggy address belongs to the page:
>>>>> page:ffffea00072ff4c0 count:1 mapcount:0 mapping:ffff8801cbfd3040 index:0x0
>>>>> flags: 0x200000000000100(slab)
>>>>> raw: 0200000000000100 ffff8801cbfd3040 0000000000000000 000000010000000f
>>>>> raw: ffffea000730c7a0 ffffea00072ff7a0 ffff8801dae069c0 0000000000000000
>>>>> page dumped because: kasan: bad access detected
>>>>>
>>>>> Memory state around the buggy address:
>>>>> ffff8801cbfd2f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>>>> ffff8801cbfd3000: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>>>>>>
>>>>>> ffff8801cbfd3080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>>
>>>>> ^
>>>>> ffff8801cbfd3100: fb fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb
>>>>> ffff8801cbfd3180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>> ==================================================================
>>>>
>>>>
>>>> I guess this is more related to mm rather than x86, so +mm maintainers.
>>>> This continues to happen, in particular on upstream
>>>> 781402340475144bb360e32bb7437fa4b84cadc3 (Oct 28).
>>>>
>>>>
>>>>> ---
>>>>> This bug is generated by a dumb bot. It may contain errors.
>>>>> See https://goo.gl/tpsmEJ for details.
>>>>> Direct all questions to syzkaller@xxxxxxxxxxxxxxxxx
>>>>>
>>>>> syzbot will keep track of this bug report.
>>>>> Once a fix for this bug is committed, please reply to this email with:
>>>>> #syz fix: exact-commit-title
>>>>> To mark this as a duplicate of another syzbot report, please reply with:
>>>>> #syz dup: exact-subject-of-another-report
>>>>> If it's a one-off invalid bug report, please reply with:
>>>>> #syz invalid
>>>>> Note: if the crash happens again, it will cause creation of a new bug
>>>>> report.
>>>>>
>>>>> --
>>>>> You received this message because you are subscribed to the Google Groups
>>>>> "syzkaller-bugs" group.
>>>>> To unsubscribe from this group and stop receiving emails from it, send an
>>>>> email to syzkaller-bugs+unsubscribe@xxxxxxxxxxxxxxxxx
>>>>> To view this discussion on the web visit
>>>>> https://groups.google.com/d/msgid/syzkaller-bugs/94eb2c0433c8f42cac055cc86991%40google.com.
>>>>> For more options, visit https://groups.google.com/d/optout.
>>>>
>>>> --
>>>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>>>> the body to majordomo@xxxxxxxxxx For more info on Linux MM,
>>>> see: http://www.linux-mm.org/ .
>>>> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
>>>>
>>>
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@xxxxxxxxxx For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
>

Next message: Dmitry Vyukov: "Re: general protection fault in gfn_to_rmap"
Previous message: Roger Quadros: "[PATCH v2][RESEND] usb: gadget: core: Fix ->udc_set_speed() speed handling"
In reply to: Vlastimil Babka: "Re: KASAN: use-after-free Read in __do_page_fault"
Next in thread: Kirill A. Shutemov: "Re: KASAN: use-after-free Read in __do_page_fault"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]