linux-kernel - [PATCH 2/5] soundwire: bus_type: protect cases where no driver name is provided

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Message-Id: <20200320162947.17663-3-pierre-louis.bossart@linux.intel.com>
Date:   Fri, 20 Mar 2020 11:29:44 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     alsa-devel@...a-project.org
Cc:     linux-kernel@...r.kernel.org, tiwai@...e.de, broonie@...nel.org,
        vkoul@...nel.org, gregkh@...uxfoundation.org, jank@...ence.com,
        srinivas.kandagatla@...aro.org, slawomir.blauciak@...el.com,
        Bard liao <yung-chuan.liao@...ux.intel.com>,
        Rander Wang <rander.wang@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Hui Wang <hui.wang@...onical.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: [PATCH 2/5] soundwire: bus_type: protect cases where no driver name is provided

When the implementation only creates a sdw_master_device and does not
provide a master_name, we have a risk of kernel oopses with dereferences
of a NULL pointer.

Protect with explicit tests.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
---
 drivers/soundwire/bus_type.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/soundwire/bus_type.c b/drivers/soundwire/bus_type.c
index 09a25075e770..c01d74c709d5 100644
--- a/drivers/soundwire/bus_type.c
+++ b/drivers/soundwire/bus_type.c
@@ -48,12 +48,14 @@ static int sdw_bus_match(struct device *dev, struct device_driver *ddrv)
 		md = dev_to_sdw_master_device(dev);
 		mdrv = drv_to_sdw_master_driver(ddrv);
 
-		/*
-		 * we don't have any hardware information so
-		 * match with a hopefully unique string
-		 */
-		ret = !strncmp(md->master_name, mdrv->driver.name,
-			       strlen(md->master_name));
+		if (md->master_name) {
+			/*
+			 * we don't have any hardware information so
+			 * match with a hopefully unique string
+			 */
+			ret = !strncmp(md->master_name, mdrv->driver.name,
+				       strlen(md->master_name));
+		}
 	}
 	return ret;
 }
@@ -71,9 +73,11 @@ static int sdw_master_modalias(const struct sdw_master_device *md,
 			       char *buf, size_t size)
 {
 	/* modalias is sdw:<string> since we don't have any hardware info */
-
-	return snprintf(buf, size, "sdw:%s\n",
-			md->master_name);
+	if (md->master_name)
+		return snprintf(buf, size, "sdw:%s\n",
+				md->master_name);
+	else
+		return snprintf(buf, size, "sdw:no_master_driver\n");
 }
 
 static int sdw_uevent(struct device *dev, struct kobj_uevent_env *env)
-- 
2.20.1