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

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Message-ID: <20190426142710.s6j2wjum2viwjf4j@pathway.suse.cz>
Date:   Fri, 26 Apr 2019 16:27:10 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 00/10] vsprintf: Prevent silent crashes and
 consolidate error handling

On Fri 2019-04-26 16:02:04, Andy Shevchenko wrote:
> On Wed, Apr 24, 2019 at 03:53:06PM +0200, Petr Mladek wrote:
> > 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@...il.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.
> 
> They are good enough to me, thanks!
> FWIW,
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

Thanks a lot. I have added the tag to the commits
in printk.git, branch for-5.2-vsprintf-hardening.

Best Regards,
Petr