linux-kernel - Re: [PATCH -next] cpufreq: Fix reserved space in cpufreq_show

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Date:   Tue, 14 Jun 2022 15:37:20 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Yi Yang <yiyang13@...wei.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] cpufreq: Fix reserved space in cpufreq_show_cpus()

On Tue, May 24, 2022 at 9:10 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 21-05-22, 14:35, Yi Yang wrote:
> > Function scnprintf() would reserve space for the trailing '\0' and return
> > value is the number of characters written into buf not including the
> > trailing '\0'. internally meaning the next scnprintf() would write begin
> > the trailing '\0'. The code specifying "PAGE_SIZE - i - 2" here is trying
> > to reserve space for "\n\0" which would cause scnprintf() to reserve an
> > additional byte making the tail of the buf looks like this: "\n\0\0".
> > Thus. we should reserve only the space for one '\0'. passing in
> > "PAGE_SIZE - i - 1".
> >
> > Additionally, each iteration would replace the trailing '\0' from the last
> > iteration with a space, and append 4 additional bytes to the string making
> > it a total of 5 additional bytes. That means we should stop printing into
> > the buffer if the remaining size is less than 7 bytes(1 for the ' ', 4 for
> > the %u and 2 for the tailing "\n\0")
> >
> > Signed-off-by: Yi Yang <yiyang13@...wei.com>
> > ---
> >  drivers/cpufreq/cpufreq.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 1f6667ce43bd..60c005c9961e 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -844,9 +844,9 @@ ssize_t cpufreq_show_cpus(const struct cpumask *mask, char *buf)
> >
> >       for_each_cpu(cpu, mask) {
> >               if (i)
> > -                     i += scnprintf(&buf[i], (PAGE_SIZE - i - 2), " ");
> > -             i += scnprintf(&buf[i], (PAGE_SIZE - i - 2), "%u", cpu);
> > -             if (i >= (PAGE_SIZE - 5))
> > +                     i += scnprintf(&buf[i], (PAGE_SIZE - i - 1), " ");
> > +             i += scnprintf(&buf[i], (PAGE_SIZE - i - 1), "%u", cpu);
> > +             if (i >= (PAGE_SIZE - 6))
> >                       break;
> >       }
> >       i += sprintf(&buf[i], "\n");
>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

Applied as 5.20 material, thanks!