linux-kernel - Re: BUG: bad usercopy in old_dev

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Date:   Tue, 19 Dec 2017 07:57:54 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot 
        <bot+5e56fb40e0f2bc3f20402f782f0b3913cb959acc@...kaller.appspotmail.com>,
        David Windsor <dave@...lcore.net>,
        James Morse <james.morse@....com>, keun-o.park@...kmatter.ae,
        Laura Abbott <labbott@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Mark Rutland <mark.rutland@....com>,
        Ingo Molnar <mingo@...nel.org>, syzkaller-bugs@...glegroups.com
Subject: Re: BUG: bad usercopy in old_dev_ioctl

On Tue, Dec 19, 2017 at 12:49 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Sun, Dec 17, 2017 at 5:45 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Sat, Dec 16, 2017 at 11:47 PM, syzbot
>> <bot+5e56fb40e0f2bc3f20402f782f0b3913cb959acc@...kaller.appspotmail.com>
>> 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.

-Kees

>
>
>>>  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@...glegroups.com.
>>> Please credit me with: Reported-by: syzbot <syzkaller@...glegroups.com>
>>>
>>> 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