Re: BUG: bad usercopy in memdup_user

[Kees Cook]

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).

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