[PATCH] request_firmware(): avoid race conditions

Avoid race occurs when some process have open file descriptor for class
device attributes and already firmware allocated memory are freed. Don't
allow negative loading timeout.

Signed-off-by: Stanislaw W. Gruszka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/base/firmware_class.c

···
 firmware_timeout_store(struct class *class, const char *buf, size_t count)
 {
 	loading_timeout = simple_strtol(buf, NULL, 10);
+	if (loading_timeout < 0)
+		loading_timeout = 0;
 	return count;
 }
 
···
 	switch (loading) {
 	case 1:
 		down(&fw_lock);
+		if (!fw_priv->fw) {
+			up(&fw_lock);
+			break;
+		}
 		vfree(fw_priv->fw->data);
 		fw_priv->fw->data = NULL;
 		fw_priv->fw->size = 0;
···
 
 	down(&fw_lock);
 	fw = fw_priv->fw;
-	if (test_bit(FW_STATUS_DONE, &fw_priv->status)) {
+	if (!fw || test_bit(FW_STATUS_DONE, &fw_priv->status)) {
 		ret_count = -ENODEV;
 		goto out;
 	}
···
 
 	if (!capable(CAP_SYS_RAWIO))
 		return -EPERM;
+
 	down(&fw_lock);
 	fw = fw_priv->fw;
-	if (test_bit(FW_STATUS_DONE, &fw_priv->status)) {
+	if (!fw || test_bit(FW_STATUS_DONE, &fw_priv->status)) {
 		retval = -ENODEV;
 		goto out;
 	}
···
 
 	fw_priv = class_get_devdata(class_dev);
 
-	if (loading_timeout) {
+	if (loading_timeout > 0) {
 		fw_priv->timeout.expires = jiffies + loading_timeout * HZ;
 		add_timer(&fw_priv->timeout);
 	}