Fix firmware loader uevent buffer NULL pointer dereference

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@osg.samsung.com>
Acked-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 9cf8dc7448e257446a54c0b4d904b37ae4321463..30d575a09ad17e62f345a3520f2b480519c800c2 100644 (file)
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -543,10 +543,8 @@ static void fw_dev_release(struct device *dev)
        module_put(THIS_MODULE);
 }
 
-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))
@@ -557,6 +555,18 @@ 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,