Re: BUG: bad usercopy in memdup_user

[Tobin C. Harding]

On Tue, Dec 19, 2017 at 09:12:58AM +0100, Dmitry Vyukov wrote:
> On Tue, Dec 19, 2017 at 1:57 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > 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).
> 
> 
> +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.

Hope this helps,
Tobin.