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Message-ID: <20171219090418.GS19604@eros> Date: Tue, 19 Dec 2017 20:04:18 +1100 From: "Tobin C. Harding" <me@...in.cc> To: Dmitry Vyukov <dvyukov@...gle.com> Cc: Kees Cook <keescook@...omium.org>, Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Linux-MM <linux-mm@...ck.org>, syzbot <bot+719398b443fd30155f92f2a888e749026c62b427@...kaller.appspotmail.com>, David Windsor <dave@...lcore.net>, keun-o.park@...kmatter.ae, Laura Abbott <labbott@...hat.com>, LKML <linux-kernel@...r.kernel.org>, Mark Rutland <mark.rutland@....com>, Ingo Molnar <mingo@...nel.org>, syzkaller-bugs@...glegroups.com, Will Deacon <will.deacon@....com> Subject: Re: BUG: bad usercopy in memdup_user On Tue, Dec 19, 2017 at 09:41:39AM +0100, Dmitry Vyukov wrote: > On Tue, Dec 19, 2017 at 9:37 AM, Tobin C. Harding <me@...in.cc> wrote: > >> > <penguin-kernel@...ove.sakura.ne.jp> 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. There is no way to disable the hashing currently built into the system. Tobin
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