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

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Date:   Mon, 23 Mar 2020 15:16:42 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, kan.liang@...ux.intel.com,
        zhe.he@...driver.com, dzickus@...hat.com, jstancek@...hat.com,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] perf cpumap: Use scnprintf instead of snprintf

On Mon, Mar 23, 2020 at 01:08:47PM +0100, Christophe JAILLET wrote:
> Le 23/03/2020 à 12:03, Dan Carpenter a écrit :
> > On Sun, Mar 22, 2020 at 06:25:23PM +0100, Christophe JAILLET wrote:
> > > '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.
> > > 
> > > Fixes: 7780c25bae59f ("perf tools: Allow ability to map cpus to nodes easily")
> > > Fixes: a24020e6b7cf6 ("perf tools: Change cpu_map__fprintf output")
> > > Fixes: 92a7e1278005b ("perf cpumap: Add cpu__max_present_cpu()")
> > > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > > ---
> > >   tools/perf/util/cpumap.c | 39 ++++++++++++++++++++-------------------
> > >   1 file changed, 20 insertions(+), 19 deletions(-)
> > > 
> > > diff --git a/tools/perf/util/cpumap.c b/tools/perf/util/cpumap.c
> > > index 983b7388f22b..b87e7ef4d130 100644
> > > --- a/tools/perf/util/cpumap.c
> > > +++ b/tools/perf/util/cpumap.c
> > > @@ -316,8 +316,8 @@ static void set_max_cpu_num(void)
> > >   		goto out;
> > >   	/* get the highest possible cpu number for a sparse allocation */
> > > -	ret = snprintf(path, PATH_MAX, "%s/devices/system/cpu/possible", mnt);
> > > -	if (ret == PATH_MAX) {
> > > +	ret = scnprintf(path, PATH_MAX, "%s/devices/system/cpu/possible", mnt);
> > > +	if (ret == PATH_MAX-1) {
> > This should be a static analysis warning.
> > 
> > But isn't this stuff userspace?  I can't figure out how to compile it on
> > Debian so I'm not sure.  There is no scnprintf() in user space.
> > 
> > regards,
> > dan carpenter
> 
> I compiled it with:
> 
>     make tools/perf
> 

Ah.  You're absolutely right.  My bad.  Sorry for that.

I was doing "cd tools/perf; make" and it told me to install glibc-dev.

regards,
dan carpenter