[PATCH 3.16.y-ckt 078/130] Fix firmware loader uevent buffer NULL pointer dereference

[Luis Henriques]

3.16.7-ckt17 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Torvalds <torvalds at linux-foundation.org>

commit 6f957724b94cb19f5c1c97efd01dd4df8ced323c upstream.

The firmware class uevent function accessed the "fw_priv->buf" buffer
without the proper locking and testing for NULL.  This is an old bug
(looks like it goes back to 2012 and commit 1244691c73b2: "firmware
loader: introduce firmware_buf"), but for some reason it's triggering
only now in 4.2-rc1.

Shuah Khan is trying to bisect what it is that causes this to trigger
more easily, but in the meantime let's just fix the bug since others are
hitting it too (at least Ingo reports having seen it as well).

Reported-and-tested-by: Shuah Khan <shuahkh at osg.samsung.com>
Acked-by: Ming Lei <ming.lei at canonical.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/base/firmware_class.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 2a1d1ae5c11d..d8e585a62caa 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -544,10 +544,8 @@ static void fw_dev_release(struct device *dev)
 	kfree(fw_priv);
 }
 
-static int firmware_uevent(struct device *dev, struct kobj_uevent_env *env)
+static int do_firmware_uevent(struct firmware_priv *fw_priv, struct kobj_uevent_env *env)
 {
-	struct firmware_priv *fw_priv = to_firmware_priv(dev);
-
 	if (add_uevent_var(env, "FIRMWARE=%s", fw_priv->buf->fw_id))
 		return -ENOMEM;
 	if (add_uevent_var(env, "TIMEOUT=%i", loading_timeout))
@@ -558,6 +556,18 @@ static int firmware_uevent(struct device *dev, struct kobj_uevent_env *env)
 	return 0;
 }
 
+static int firmware_uevent(struct device *dev, struct kobj_uevent_env *env)
+{
+	struct firmware_priv *fw_priv = to_firmware_priv(dev);
+	int err = 0;
+
+	mutex_lock(&fw_lock);
+	if (fw_priv->buf)
+		err = do_firmware_uevent(fw_priv, env);
+	mutex_unlock(&fw_lock);
+	return err;
+}
+
 static struct class firmware_class = {
 	.name		= "firmware",
 	.class_attrs	= firmware_class_attrs,