linux-kernel - Re: [PATCH 1/6] pstore: Add console log messages support

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Date:	Wed, 16 May 2012 17:47:00 -0700
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>, Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Shuah Khan <shuahkhan@...il.com>, arve@...roid.com,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	Jesper Juhl <jj@...osbits.net>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Thomas Meyer <thomas@...3r.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com
Subject: Re: [PATCH 1/6] pstore: Add console log messages support

On Wed, May 16, 2012 at 03:33:45PM -0700, Anton Vorontsov wrote:
> On Wed, May 16, 2012 at 09:49:11AM -0700, Kees Cook wrote:
> [...]
> > > +#ifdef CONFIG_PSTORE_CONSOLE
> > > +static void pstore_console_write(struct console *con, const char *s, unsigned c)
> > > +{
> > > +       strncpy(psinfo->buf, s, c);
> > 
> > The size of psinfo->buf needs to be the length argument to strncpy,
> > not the size of "s". If "s" isn't NULL terminated, then the min of c
> > and buf's size should be used. And if this should be NULL terminated
> > in buf, that needs to be added manually since strncpy won't do it if
> > it hits the max length argument.
> 
> Whoops. Will fix it, thanks!

Actually, we shouldn't bother with NUL-termination at all. We should
do, is just carefully copy all 'c' elements of 's' into pstore in
'pstore->bufsize' chunks.

So, the code should be something along these lines:

static void pstore_console_write(struct console *con, const char *s, unsigned c)
{
        const char *e = s + c;

        while (s < e) {
                if (c > psinfo->bufsize)
                        c = psinfo->bufsize;
                memcpy(psinfo->buf, s, c);
                psinfo->write(PSTORE_TYPE_CONSOLE, 0, NULL, 0, c, psinfo);
                s += c;
                c = e - s;
        }
}

Here, in case of c > bufsize, we can't just copy bufsize bytes once and
exit, since 'bufsize' doesn't tell anything about TYPE_CONSOLE's internal
storage size (today console's persistent ram zone size and pstore's
bufsize are equal, but this is something we may change soon, i.e. make
TYPE_DMESG and TYPE_CONSOLE record sizes configurable).

Thanks,

-- 
Anton Vorontsov
Email: cbouatmailru@...il.com
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