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

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Message-ID: <20190419015112.GA18748@jagdpanzerIV>
Date:   Fri, 19 Apr 2019 10:51:12 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 00/10] vsprintf: Prevent silent crashes and
 consolidate error handling

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>

	-ss