Re: BUG: bad usercopy in old_dev_ioctl

[Dmitry Vyukov]

On Tue, Dec 19, 2017 at 4:57 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>> <bot+5e56fb40e0f2bc3f20402f782f0b3913cb959acc@xxxxxxxxxxxxxxxxxxxxxxxxx>
>>> 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.
>>>>
>>>>
>>>> device gre0 entered promiscuous mode
>>>> usercopy: kernel memory exposure attempt detected from 00000000a6830059
>>>> (kmalloc-1024) (1024 bytes)
>>>> ------------[ cut here ]------------
>>>> kernel BUG at mm/usercopy.c:84!
>>>> invalid opcode: 0000 [#1] SMP
>>>> Dumping ftrace buffer:
>>>>    (ftrace buffer empty)
>>>> Modules linked in:
>>>> CPU: 1 PID: 28799 Comm: syz-executor4 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:ffffc9000116fc50 EFLAGS: 00010286
>>>> RAX: 0000000000000063 RBX: ffffffff82e6518f RCX: ffffffff8123dede
>>>> RDX: 0000000000004c58 RSI: ffffc900050ed000 RDI: ffff88021fd136f8
>>>> RBP: ffffc9000116fc88 R08: 0000000000000000 R09: 0000000000000000
>>>> R10: 0000000000000000 R11: 0000000000000000 R12: ffff880216bb6050
>>>> R13: 0000000000000400 R14: 0000000000000001 R15: ffffffff82eda864
>>>> FS:  00007f61a06bc700(0000) GS:ffff88021fd00000(0000) knlGS:0000000000000000
>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> CR2: 0000000020a5afd8 CR3: 000000020f8a9000 CR4: 00000000001406e0
>>>> Call Trace:
>>>>  check_object_size include/linux/thread_info.h:112 [inline]
>>>>  check_copy_size include/linux/thread_info.h:143 [inline]
>>>>  copy_to_user include/linux/uaccess.h:154 [inline]
>>>>  old_dev_ioctl.isra.1+0x21d/0x9a0 net/bridge/br_ioctl.c:178
>>>
>>> Uhh, this doesn't make sense, much like the other report...
>>>
>>>                 indices = kcalloc(num, sizeof(int), GFP_KERNEL);
>>>                 if (indices == NULL)
>>>                         return -ENOMEM;
>>>
>>>                 get_port_ifindices(br, indices, num);
>>>                 if (copy_to_user((void __user *)args[1], indices,
>>> num*sizeof(int)))
>>>
>>> offset is 0. size overlaps. usercopy checks in -next must be broken. I
>>> will double-check.
>>
>>
>> Start of heap object ending at 0x59 looks bogus, right?
>
> No, that's a hashed address. %p doesn't report real addresses any more.

Ah, for some reason I thought that 64-bit hashing just strips upper
part (because what would be a reason to strip it from a hash? and
showing lower bytes is useful and does not reveal too much).

>>>>  br_dev_ioctl+0x3f/0xa0 net/bridge/br_ioctl.c:392
>>>>  dev_ifsioc+0x175/0x520 net/core/dev_ioctl.c:354
>>>>  dev_ioctl+0x548/0x7a0 net/core/dev_ioctl.c:589
>>>>  sock_ioctl+0x150/0x320 net/socket.c:998
>>>>  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: 0033:0x452a39
>>>> RSP: 002b:00007f61a06bbc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
>>>> RAX: ffffffffffffffda RBX: 00007f61a06bc700 RCX: 0000000000452a39
>>>> RDX: 0000000020a59fd8 RSI: 00000000000089f0 RDI: 0000000000000014
>>>> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
>>>> R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
>>>> R13: 0000000000a6f7ff R14: 00007f61a06bc9c0 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: ffffc9000116fc50
>>>> RIP: __check_object_size+0x1e2/0x250 mm/usercopy.c:276 RSP: ffffc9000116fc50
>>>> ---[ end trace 5fadb883cda020dc ]---
>>>> Kernel panic - not syncing: Fatal exception
>>>> Dumping ftrace buffer:
>>>>    (ftrace buffer empty)
>>>> Kernel Offset: disabled
>>>> Rebooting in 86400 seconds..
>>>>
>>>>
>>>> ---
>>>> 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
>>>> Please credit me with: Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
>>>>
>>>> syzbot will keep track of this bug report.
>>>> Once a fix for this bug is merged into any tree, 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.
>>>> Note: all commands must start from beginning of the line in the email body.
>>>
>>>
>>>
>>> --
>>> Kees Cook
>>> Pixel Security
>>>
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>
>
>
> --
> Kees Cook
> Pixel Security