linux-kernel - Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CACT4Y+YEx5PF7QqaLdYpkyBCr_eBgp1n2yuY2LyrN9iZANXgzQ@mail.gmail.com>
Date:   Sat, 16 Mar 2019 15:16:38 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel
 panic - not syncing: panic_on_warn set ..."

On Sat, Mar 16, 2019 at 3:14 PM Sergey Senozhatsky
<sergey.senozhatsky@...il.com> wrote:
>
> On (03/16/19 19:18), Tetsuo Handa wrote:
> > On 2019/03/16 18:11, Dmitry Vyukov wrote:
> > > Such reports showed up always with low frequency. For all that I
> > > looked at we also always had a normal  non-truncated version, so I was
> > > never too worried.
> > >
> > > If something would write from userspace, that would show up in the
> > > output, or not?
> > >
> > > Perhaps syzkaller somehow manages to lower console output level?
> >
> > panic() calls console_verbose() before calling
> >
> >   pr_emerg("Kernel panic - not syncing: %s\n", buf);
> >
> > line. Then, someone might have changed console_loglevel enough to
> > suppress printk() output.
>
> Hmm... sysctl, may be?
>
> > > I figured out that we should restrict it from doing
> > > syslog(SYSLOG_ACTION_CONSOLE_OFF). And I also restricted its access o
> > > /dev/console. But maybe there is something else? It _should_ not be
> > > able to write to random sysctl's.
> >
> > Maybe try running with "ignore_loglevel" kernel command line option added?
>
> Right, that's something I would expect 0-day and syzkaller to do.

to double-check: enabling this won't lead to verbose/debug level of logging?