[PATCH V2 1/2] tools/perf: Fix out of bound access to affinity "sched_cpus"

[Athira Rajeev]

The affinity code in "affinity_set" function access array
named "sched_cpus". The size for this array is allocated in
affinity_setup function which is nothing but value from
get_cpu_set_size. This is used to contain the cpumask value
for each cpu. While setting bit for each cpu, it calls
"set_bit" function which access index in sched_cpus array.
If we provide a command-line option to -C which is more than
the number of CPU's present in the system, the set_bit could
access an array member which is out-of the array size. This
is because currently, there is no boundary check for the CPU.
This will result in seg fault:

<<>>
 ./perf stat -C 12323431 ls
Perf can support 2048 CPUs. Consider raising MAX_NR_CPUS
Segmentation fault (core dumped)
<<>>

Fix this by adding boundary check for the array.

After the fix from powerpc system:

<<>>
./perf stat -C 12323431 ls 1>out
Perf can support 2048 CPUs. Consider raising MAX_NR_CPUS

 Performance counter stats for 'CPU(s) 12323431':

   <not supported> msec cpu-clock
   <not supported>      context-switches
   <not supported>      cpu-migrations
   <not supported>      page-faults
   <not supported>      cycles
   <not supported>      instructions
   <not supported>      branches
   <not supported>      branch-misses

       0.001192373 seconds time elapsed
<<>>

Reported-by: Nageswara Sastry <rnsastry at linux.ibm.com>
Tested-by: Nageswara Sastry <rnsastry at linux.ibm.com>
Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
---
Changelog:
 From v1 -> v2:
 Addressed review comment from Jiri Olsa by changing condition
 check to directly use "cpu_set_size * 8" for comparing with the
 cpu number.

 tools/perf/util/affinity.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/affinity.c b/tools/perf/util/affinity.c
index 4d216c0dc425..4ee96b3c755b 100644
--- a/tools/perf/util/affinity.c
+++ b/tools/perf/util/affinity.c
@@ -49,8 +49,14 @@ void affinity__set(struct affinity *a, int cpu)
 {
 	int cpu_set_size = get_cpu_set_size();
 
-	if (cpu == -1)
+	/*
+	 * Return:
+	 * - if cpu is -1
+	 * - restrict out of bound access to sched_cpus
+	 */
+	if (cpu == -1 || ((cpu >= (cpu_set_size * 8))))
 		return;
+
 	a->changed = true;
 	set_bit(cpu, a->sched_cpus);
 	/*
-- 
2.35.1