linux-kernel - Re: [PATCH 2/2] perf tools: Fix strbuf_addf() when the buffer needs to grow

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Date:	Wed, 24 Oct 2012 09:49:42 +0200
From:	Andrew Jones <drjones@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] perf tools: Fix strbuf_addf() when the buffer needs
 to grow

On Tue, Oct 23, 2012 at 10:44:50PM +0900, Namhyung Kim wrote:
> This was found during chasing down the header output regression.
> The strbuf_addf() was checking buffer length with a result of
> vscnprintf() which cannot be greater than that of strbuf_avail().
> 
> Since numa topology and pmu mapping info in header were converted
> to use strbuf, it sometimes caused uninteresting behaviors with the
> broken strbuf.
> 
> Fix it by using vsnprintf() which returns desired output string
> length regardless of the available buffer size and grow the buffer
> if needed.
> 
> Reported-by: Andrew Jones <drjones@...hat.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/util/strbuf.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/strbuf.c b/tools/perf/util/strbuf.c
> index 2eeb51baf077..cfa906882e2c 100644
> --- a/tools/perf/util/strbuf.c
> +++ b/tools/perf/util/strbuf.c
> @@ -90,17 +90,17 @@ void strbuf_addf(struct strbuf *sb, const char *fmt, ...)
>  	if (!strbuf_avail(sb))
>  		strbuf_grow(sb, 64);
>  	va_start(ap, fmt);
> -	len = vscnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
> +	len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
>  	va_end(ap);
>  	if (len < 0)
> -		die("your vscnprintf is broken");
> +		die("your vsnprintf is broken");
>  	if (len > strbuf_avail(sb)) {
>  		strbuf_grow(sb, len);
>  		va_start(ap, fmt);
> -		len = vscnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
> +		len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
>  		va_end(ap);
>  		if (len > strbuf_avail(sb)) {
> -			die("this should not happen, your snprintf is broken");
> +			die("this should not happen, your vsnprintf is broken");
>  		}
>  	}
>  	strbuf_setlen(sb, sb->len + len);
> -- 
> 1.7.9.2
>

Tested-by: Andrew Jones <drjones@...hat.com> 
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