linux-kernel - RE: [PATCH] perf cpumap: Use scnprintf instead of snprintf

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Date:   Mon, 23 Mar 2020 15:11:40 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christophe JAILLET' <christophe.jaillet@...adoo.fr>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
        "zhe.he@...driver.com" <zhe.he@...driver.com>,
        "dzickus@...hat.com" <dzickus@...hat.com>,
        "jstancek@...hat.com" <jstancek@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: RE: [PATCH] perf cpumap: Use scnprintf instead of snprintf

From: Christophe JAILLET
> Sent: 22 March 2020 17:25
> 'scnprintf' returns the number of characters written in the output buffer
> excluding the trailing '\0', instead of the number of characters which
> would be generated for the given input.
> 
> Both function return a number of characters, excluding the trailing '\0'.
> So comparaison to check if it overflows, should be done against max_size-1.
> Comparaison against max_size can never match.

NACK.
Since snprintf() returns the number of characters it would have
written to an infinite buffer the comparison can 'match'.

However it should test for (ret >= PATH_MAX).

	David

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