[PATCH] PM / devfreq: Fix out of bounds access of transition table array

[Saravana Kannan]

The previous_freq value for a device could be an invalid frequency that
results in a error value being returned from devfreq_get_freq_level().
Check for an error value before using that to index into the transition
table.

Not doing this check will result in memory corruption when previous_freq is
not a valid frequency.

Signed-off-by: Saravana Kannan <skannan at codeaurora.org>
---
 drivers/devfreq/devfreq.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index a0b2f7e..f91ea29 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -101,14 +101,20 @@ static int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
 	cur_time = jiffies;
 	devfreq->time_in_state[lev] +=
 			 cur_time - devfreq->last_stat_updated;
-	if (freq != devfreq->previous_freq) {
-		prev_lev = devfreq_get_freq_level(devfreq,
-						devfreq->previous_freq);
+	devfreq->last_stat_updated = cur_time;
+
+	if (freq == devfreq->previous_freq)
+		return 0;
+
+	prev_lev = devfreq_get_freq_level(devfreq, devfreq->previous_freq);
+	if (prev_lev < 0)
+		return 0;
+
+	if (lev != prev_lev) {
 		devfreq->trans_table[(prev_lev *
 				devfreq->profile->max_state) + lev]++;
 		devfreq->total_trans++;
 	}
-	devfreq->last_stat_updated = cur_time;
 
 	return 0;
 }
-- 
1.8.2.1

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