Re: [PATCH 1/3] cpufreq: fix broken buffer overflow detection in trans_stats

[Rafael J. Wysocki]

On Thu, Oct 26, 2023 at 12:54 PM Christian Marangi <ansuelsmth@xxxxxxxxx> wrote:
>
> On Tue, Oct 24, 2023 at 10:03:35PM +0200, Rafael J. Wysocki wrote:
> > On Tue, Oct 24, 2023 at 8:30 PM Christian Marangi <ansuelsmth@xxxxxxxxx> wrote:
> > >
> > > Commit 3c0897c180c6 ("cpufreq: Use scnprintf() for avoiding potential
> > > buffer overflow") switched from snprintf to the more secure scnprintf
> > > but never updated the exit condition for PAGE_SIZE.
> > >
> > > As the commit say and as scnprintf document, what scnprintf returns what
> > > is actually written not counting the '\0' end char. This results in the
> > > case of len exceeding the size, len set to PAGE_SIZE - 1, as it can be
> > > written at max PAGESIZE - 1 (as '\0' is not counted)
> > >
> > > Because of len is never set to PAGE_SIZE, the function never break early,
> > > never print the warning and never return -EFBIG.
> > >
> > > Fix this by fixing the condition to PAGE_SIZE -1 to correctly trigger
> > > the error condition.
> > >
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Fixes: 3c0897c180c6 ("cpufreq: Use scnprintf() for avoiding potential buffer overflow")
> > > Signed-off-by: Christian Marangi <ansuelsmth@xxxxxxxxx>
> > > ---
> > >  drivers/cpufreq/cpufreq_stats.c | 14 +++++++-------
> > >  1 file changed, 7 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
> > > index a33df3c66c88..40a9ff18da06 100644
> > > --- a/drivers/cpufreq/cpufreq_stats.c
> > > +++ b/drivers/cpufreq/cpufreq_stats.c
> > > @@ -131,23 +131,23 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
> > >         len += sysfs_emit_at(buf, len, "   From  :    To\n");
> > >         len += sysfs_emit_at(buf, len, "         : ");
> > >         for (i = 0; i < stats->state_num; i++) {
> > > -               if (len >= PAGE_SIZE)
> > > +               if (len >= PAGE_SIZE - 1)
> > >                         break;
> > >                 len += sysfs_emit_at(buf, len, "%9u ", stats->freq_table[i]);
> > >         }
> > > -       if (len >= PAGE_SIZE)
> > > -               return PAGE_SIZE;
> > > +       if (len >= PAGE_SIZE - 1)
> > > +               return PAGE_SIZE - 1;
> > >
> > >         len += sysfs_emit_at(buf, len, "\n");
> > >
> > >         for (i = 0; i < stats->state_num; i++) {
> > > -               if (len >= PAGE_SIZE)
> > > +               if (len >= PAGE_SIZE - 1)
> > >                         break;
> > >
> > >                 len += sysfs_emit_at(buf, len, "%9u: ", stats->freq_table[i]);
> > >
> > >                 for (j = 0; j < stats->state_num; j++) {
> > > -                       if (len >= PAGE_SIZE)
> > > +                       if (len >= PAGE_SIZE - 1)
> > >                                 break;
> > >
> > >                         if (pending)
> > > @@ -157,12 +157,12 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
> > >
> > >                         len += sysfs_emit_at(buf, len, "%9u ", count);
> > >                 }
> > > -               if (len >= PAGE_SIZE)
> > > +               if (len >= PAGE_SIZE - 1)
> > >                         break;
> > >                 len += sysfs_emit_at(buf, len, "\n");
> > >         }
> > >
> > > -       if (len >= PAGE_SIZE) {
> > > +       if (len >= PAGE_SIZE - 1) {
> > >                 pr_warn_once("cpufreq transition table exceeds PAGE_SIZE. Disabling\n");
> > >                 return -EFBIG;
> > >         }
> > > --
> >
> > Applied (with some edits in the subject and changelog) as 6.7 material, thanks!
>
> Hi, I just notice this landed in linux-next but I can't find the devfreq
> change. Only the cpufreq patch has been taken and the devfreq ones are
> still pending?

That's correct AFAICS.  I've only picked up the cpufreq change.