Re: BUG: bad usercopy in memdup_user

[Dmitry Vyukov]

On Tue, Dec 19, 2017 at 1:57 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Mon, Dec 18, 2017 at 6:22 AM, Tetsuo Handa
> <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
>> On 2017/12/18 22:40, syzbot wrote:
>>> Hello,
>>>
>>> syzkaller hit the following crash on 6084b576dca2e898f5c101baef151f7bfdbb606d
>>> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
>>> compiler: gcc (GCC) 7.1.1 20170620
>>> .config is attached
>>> Raw console output is attached.
>>>
>>> Unfortunately, I don't have any reproducer for this bug yet.
>>>
>>>
>>
>> This BUG is reporting
>>
>> [   26.089789] usercopy: kernel memory overwrite attempt detected to 0000000022a5b430 (kmalloc-1024) (1024 bytes)
>>
>> line. But isn't 0000000022a5b430 strange for kmalloc(1024, GFP_KERNEL)ed kernel address?
>
> The address is hashed (see the %p threads for 4.15).


+Tobin, is there a way to disable hashing entirely? The only
designation of syzbot is providing crash reports to kernel developers
with as much info as possible. It's fine for it to leak whatever.


> There's something strange going on with the slab allocator (I haven't
> tracked it down yet, unfortunately).
>
> -Kees
>
>>
>>> netlink: 1 bytes leftover after parsing attributes in process `syz-executor5'.
>>> ------------[ cut here ]------------
>>> kernel BUG at mm/usercopy.c:84!
>>> invalid opcode: 0000 [#1] SMP
>>> Dumping ftrace buffer:
>>>    (ftrace buffer empty)
>>> Modules linked in:
>>> CPU: 0 PID: 3943 Comm: syz-executor0 Not tainted 4.15.0-rc3-next-20171214+ #67
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>> RIP: 0010:report_usercopy mm/usercopy.c:76 [inline]
>>> RIP: 0010:__check_object_size+0x1e2/0x250 mm/usercopy.c:276
>>> RSP: 0018:ffffc90000d6fca8 EFLAGS: 00010292
>>> RAX: 0000000000000062 RBX: ffffffff82e57be7 RCX: ffffffff8123dede
>>> RDX: 0000000000006340 RSI: ffffc900036c9000 RDI: ffff88021fc136f8
>>> RBP: ffffc90000d6fce0 R08: 0000000000000000 R09: 0000000000000000
>>> R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801e076dc50
>>> R13: 0000000000000400 R14: 0000000000000000 R15: ffffffff82edf8a5
>>> FS:  00007fe747e20700(0000) GS:ffff88021fc00000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 000000002000bffa CR3: 00000001dbd02006 CR4: 00000000001626f0
>>> DR0: 0000000020000000 DR1: 0000000000010000 DR2: 000000000000f004
>>> DR3: 0000000000000000 DR6: 00000000fffe0ff3 DR7: 0000000000000600
>>> Call Trace:
>>>  check_object_size include/linux/thread_info.h:112 [inline]
>>>  check_copy_size include/linux/thread_info.h:143 [inline]
>>>  copy_from_user include/linux/uaccess.h:146 [inline]
>>>  memdup_user+0x46/0x90 mm/util.c:168
>>>  kvm_arch_vcpu_ioctl+0xc85/0x1810 arch/x86/kvm/x86.c:3499
>>>  kvm_vcpu_ioctl+0xf3/0x820 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2715
>>>  vfs_ioctl fs/ioctl.c:46 [inline]
>>>  do_vfs_ioctl+0xaf/0x840 fs/ioctl.c:686
>>>  SYSC_ioctl fs/ioctl.c:701 [inline]
>>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>>>  entry_SYSCALL_64_fastpath+0x1f/0x96
>>> RIP: 0033:0x452a09
>>> RSP: 002b:00007fe747e1fc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
>>> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452a09
>>> RDX: 0000000020ebec00 RSI: 000000004400ae8f RDI: 0000000000000019
>>> RBP: 000000000000023b R08: 0000000000000000 R09: 0000000000000000
>>> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f0628
>>> R13: 00000000ffffffff R14: 00007fe747e206d4 R15: 0000000000000000
>>> Code: 7b e5 82 48 0f 44 da e8 8d 82 eb ff 48 8b 45 d0 4d 89 e9 4c 89 e1 4c 89 fa 48 89 de 48 c7 c7 a8 51 e6 82 49 89 c0 e8 76 b7 e3 ff <0f> 0b 48 c7 c0 43 51 e6 82 eb a1 48 c7 c0 53 51 e6 82 eb 98 48
>>> RIP: report_usercopy mm/usercopy.c:76 [inline] RSP: ffffc90000d6fca8
>>> RIP: __check_object_size+0x1e2/0x250 mm/usercopy.c:276 RSP: ffffc90000d6fca8
>>> ---[ end trace 189465b430781fff ]---
>>> Kernel panic - not syncing: Fatal exception
>>> Dumping ftrace buffer:
>>>    (ftrace buffer empty)
>>> Kernel Offset: disabled
>>> Rebooting in 86400 seconds..
>
>
>
> --
> Kees Cook
> Pixel Security
>
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