Re: BUG: bad usercopy in memdup_user

[Dmitry Vyukov]

On Tue, Dec 19, 2017 at 9:37 AM, Tobin C. Harding <me@xxxxxxxx> wrote:
>> > <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.
>
> We have new specifier %px to print addresses in hex if leaking info is
> not a worry.

This is not a per-printf-site thing. It's per-machine thing.