tools/thermal: tmon: fix for segfault

Fixes a segfault occurring when e.g. <TAB> is pressed multiple times in the
ncurses tmon application. The segfault is caused by incrementing
cur_thermal_record in the main function without checking if it's value reached
NR_THERMAL_RECORD immediately. Since the boundary check only occurred in
update_thermal_data a race condition existed, which lead to an attempted read
beyond the last element of the trec array.

The fix was implemented by moving the cur_thermal_record incrementation to the
update_thermal_data function using a temporary variable on which the boundary
condition is checked before updating cur_thread_record, so that the variable is
never incremented beyond the trec array's boundary.

It seems the segfault does not occur on every machine: On a HP EliteBook G4 the
segfault happens, while it does not happen on a Thinkpad T540p.

Signed-off-by: Frank Asseg <frank.asseg@objecthunter.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

2 files changed, 7 insertions, 6 deletions

diff --git a/tools/thermal/tmon/sysfs.c b/tools/thermal/tmon/sysfs.c
index 1c12536f2081..18f523557983 100644
--- a/tools/thermal/tmon/sysfs.c
+++ b/tools/thermal/tmon/sysfs.c
@@ -486,6 +486,7 @@ int zone_instance_to_index(int zone_inst)
 int update_thermal_data()
 {
         int i;
+        int next_thermal_record = cur_thermal_record + 1;
         char tz_name[256];
         static unsigned long samples;
 
@@ -495,9 +496,9 @@ int update_thermal_data()
         }
 
         /* circular buffer for keeping historic data */
-        if (cur_thermal_record >= NR_THERMAL_RECORDS)
-                cur_thermal_record = 0;
-        gettimeofday(&trec[cur_thermal_record].tv, NULL);
+        if (next_thermal_record >= NR_THERMAL_RECORDS)
+                next_thermal_record = 0;
+        gettimeofday(&trec[next_thermal_record].tv, NULL);
         if (tmon_log) {
                 fprintf(tmon_log, "%lu ", ++samples);
                 fprintf(tmon_log, "%3.1f ", p_param.t_target);
@@ -507,11 +508,12 @@ int update_thermal_data()
                 snprintf(tz_name, 256, "%s/%s%d", THERMAL_SYSFS, TZONE,
                         ptdata.tzi[i].instance);
                 sysfs_get_ulong(tz_name, "temp",
-                                &trec[cur_thermal_record].temp[i]);
+                                &trec[next_thermal_record].temp[i]);
                 if (tmon_log)
                         fprintf(tmon_log, "%lu ",
-                                trec[cur_thermal_record].temp[i]/1000);
+                                trec[next_thermal_record].temp[i] / 1000);
         }
+        cur_thermal_record = next_thermal_record;
         for (i = 0; i < ptdata.nr_cooling_dev; i++) {
                 char cdev_name[256];
                 unsigned long val;
diff --git a/tools/thermal/tmon/tmon.c b/tools/thermal/tmon/tmon.c
index 9aa19652e8e8..b43138f8b862 100644
--- a/tools/thermal/tmon/tmon.c
+++ b/tools/thermal/tmon/tmon.c
@@ -336,7 +336,6 @@ int main(int argc, char **argv)
                         show_data_w();
                         show_cooling_device();
                 }
-                cur_thermal_record++;
                 time_elapsed += ticktime;
                 controller_handler(trec[0].temp[target_tz_index] / 1000,
                                 &yk);