Re: [PATCH v7 00/10] vsprintf: Prevent silent crashes and consolidate error handling

From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"Tobin C . Harding" <me@tobin.cc>, Joe Perches <joe@perches.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.cz>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 00/10] vsprintf: Prevent silent crashes and consolidate error handling
Date: Wed, 24 Apr 2019 15:53:06 +0200	[thread overview]
Message-ID: <20190424135306.xiuhj6dmzrgytulp@pathway.suse.cz> (raw)
In-Reply-To: <20190419015112.GA18748@jagdpanzerIV>

On Fri 2019-04-19 10:51:12, Sergey Senozhatsky wrote:
> On (04/17/19 13:53), Petr Mladek wrote:
> > Crash in vsprintf() might be silent when it happens under logbuf_lock
> > in vprintk_emit(). This patch set prevents most of the crashes by probing
> > the address. The check is done only by %s and some %p* specifiers that need
> > to dereference the address.
> >
> > Only the first byte of the address is checked to keep it simple. It should
> > be enough to catch most problems.
> >
> > The check is explicitly done in each function that does the dereference.
> > It helps to avoid the questionable strchr() of affected specifiers. This
> > change motivated me to do some preparation patches that consolidated
> > the error handling and cleaned the code a bit.
> 
> The patch set looks OK to me.
> 
> I got confused by 'pC?' error string, but once you start looking
> at it as a regex (? - zero or one occurrences) things look OK.
> Regex in dmesg/serial output might be something very new to people,
> stack traces, after all, is a rather common error reporting mechanism.
> So the previous "WARN_ON() + exact unrecognized fmt[N] char" was not
> totally awful or wrong (well, it was, before we introduced printk_safe()),
> but I don't have strong objections against that new regex thing.
> 
> FWIW,
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

Thanks a lot for review.

I have pushed the entire patchset into printk.git,
branch for-5.2-vsprintf-hardening to get some
test coverage via linux-next.

I still expect some feedback, especially from Andy
who seems to have a vacation these days.
I think that Andy wanted these changes rather sooner
than later, so I hope that he would be fine with it.
I could take it back in case of disagreement.

Best Regards,
Petr