cpufreq: Avoid potential buffer overrun and leak

If set_px_pminfo is called a second time with a larger state_count than
the first call, calls to PMSTAT_get_pxstat will read beyond the end of
the pt and trans_pt buffers allocated in cpufreq_statistic_init() since
they would have been allocated with the original state_count.

Secondly, the states array leaks on each subsequent call of
set_px_pminfo.

Fix both these issues by ignoring subsequent calls to set_px_pminfo if
it completed successfully previously. Return success rather than an
error to avoid errors in the dom0 kernel log when reloading the
xen_acpi_processor module.

At the same time, fix a leak of the states array on error.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/drivers/cpufreq/cpufreq.c

@@ -517,7 +517,7 @@ int set_px_pminfo(uint32_t acpi_id, struct xen_processor_performance *perf)
         }
     }
 
-    if ( perf->flags & XEN_PX_PSS )
+    if ( perf->flags & XEN_PX_PSS && !pxpt->states )
     {
         /* capability check */
         if ( perf->state_count <= 1 )
@@ -534,6 +534,7 @@ int set_px_pminfo(uint32_t acpi_id, struct xen_processor_performance *perf)
         }
         if ( copy_from_guest(pxpt->states, perf->states, perf->state_count) )
         {
+            XFREE(pxpt->states);
             ret = -EFAULT;
             goto out;
         }