linux-kernel - [PATCH AUTOSEL for 4.15 026/124] PM / devfreq: Fix potential NULL pointer dereference in governor

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Message-ID: <20180319154645.11350-26-alexander.levin@microsoft.com>
Date:   Mon, 19 Mar 2018 15:47:25 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.15 026/124] PM / devfreq: Fix potential NULL
 pointer dereference in governor_store

From: "Gustavo A. R. Silva" <garsilva@...eddedor.com>

[ Upstream commit 63f1e05f7fe9ca509c60154d6a833abf96eecdc9 ]

df->governor is being dereferenced before it is null checked,
hence there is a potential null pointer dereference.

Notice that df->governor is being null checked at line 1004:
if (df->governor) {, which implies it might be null.

Fix this by null checking df->governor before dereferencing it.

Addresses-Coverity-ID: 1401988 ("Dereference before null check")
Fixes: bcf23c79c4e4 ("PM / devfreq: Fix available_governor sysfs")
Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@...sung.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/devfreq/devfreq.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 99c4021fc33b..fe2af6aa88fc 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -996,7 +996,8 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
 	if (df->governor == governor) {
 		ret = 0;
 		goto out;
-	} else if (df->governor->immutable || governor->immutable) {
+	} else if ((df->governor && df->governor->immutable) ||
+					governor->immutable) {
 		ret = -EINVAL;
 		goto out;
 	}
-- 
2.14.1