linux-kernel - Re: [PATCH] kconfig: Add kernel config option for fuzz testing.

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Message-ID: <46e8f6b3-46ac-6600-ba40-9545b7e44016@i-love.sakura.ne.jp>
Date:   Tue, 17 Dec 2019 06:06:54 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Jiri Slaby <jslaby@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] kconfig: Add kernel config option for fuzz testing.

On 2019/12/17 5:18, Theodore Y. Ts'o wrote:
>> this case was too hard to blacklist, as explained at
>> https://lore.kernel.org/lkml/4d1a4b51-999b-63c6-5ce3-a704013cecb6@i-love.sakura.ne.jp/ .
>> syz_execute_func() can find deeper bug by executing arbitrary binary code, but
>> we cannot blacklist specific syscalls/arguments for syz_execute_func() testcases.
>> Unless we guard on the kernel side, we won't be able to re-enable syz_execute_func()
>> testcases.
> 
> I looked at the reference, but I didn't see the explanation in the
> above link about why it was "too hard to blacklist".  In fact, it
> looks like a bit earlier in the thread, Dmitry stated that adding this
> find of blacklist "is not hard"?
> 
> https://lore.kernel.org/lkml/CACT4Y+Z_+H09iOPzSzJfs=_D=dczk22gL02FjuZ6HXO+p0kRyA@mail.gmail.com/
> 

That thread handled two bugs which disabled console output.

The former bug (March 2019) was that fuzzer was calling syslog(SYSLOG_ACTION_CONSOLE_LEVEL) and
was fixed by blacklisting syslog(SYSLOG_ACTION_CONSOLE_LEVEL). This case was easy to blacklist.

The latter bug (May 2019) was that fuzzer was calling binary code (via syz_execute_func()) which
emdebbed a system call that changes console loglevel. Since it was too difficult to blacklist,
syzkaller gave up use of syz_execute_func().