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

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Message-Id: <201903190041.x2J0ff1x060125@www262.sakura.ne.jp>
Date:   Tue, 19 Mar 2019 09:41:41 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        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 ..."

Dmitry Vyukov wrote:
> On Mon, Mar 18, 2019 at 1:32 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > Wait, but isn't SYSLOG_ACTION_CONSOLE_LEVEL what we are looking for?
> > syzkaller knows about the syslog syscall:
> > https://github.com/google/syzkaller/blob/13026d10f09f0e801c342e6c009ff580d49b894b/sys/linux/sys.txt#L322
> > and even though it does not know SYSLOG_ACTION_CONSOLE_LEVEL const, it
> > can guess that number.
> 
> I've restricted fuzzer from invoking SYSLOG_ACTION_CONSOLE_LEVEL.
> Let's see if it helps.
> 

Oh, coverage page says that

        /* Set level of messages printed to console */
        case SYSLOG_ACTION_CONSOLE_LEVEL:
                if (len < 1 || len > 8) /*covered*/
                        return -EINVAL;
                if (len < minimum_console_loglevel) /*covered*/
                        len = minimum_console_loglevel;
                console_loglevel = len;
                /* Implicitly re-enable logging to console */
                saved_console_loglevel = LOGLEVEL_DEFAULT;
                break;

fuzzer was indeed testing SYSLOG_ACTION_CONSOLE_LEVEL case. ;-)