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Date:   Sun, 31 Dec 2017 09:10:13 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Kees Cook <keescook@...omium.org>
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 5:35 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Tue, Dec 19, 2017 at 4:57 PM, Kees Cook <keescook@...omium.org> wrote:
>>>> <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.
>
> 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@...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.

Bad things on kmalloc-1024 are most likely caused by an invalid free
in pcrypt, it freed a pointer into a middle of a 1024 byte heap object
which was undetected by KASAN (now there is a patch for this in mm
tree) and later caused all kinds of bad things:
https://groups.google.com/forum/#!topic/syzkaller-bugs/NKn_ivoPOpk
https://patchwork.kernel.org/patch/10126761/

#syz dup: KASAN: use-after-free Read in __list_del_entry_valid (2)

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