linux-kernel - Re: Inconsistency in usb_add_gadget_udc

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Date:   Wed, 16 Aug 2017 11:24:52 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Alexey Khoroshilov <khoroshilov@...ras.ru>
cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Opasiak <k.opasiak@...sung.com>,
        Anton Vasilyev <vasilyev@...ras.ru>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <ldv-project@...uxtesting.org>
Subject: Re: Inconsistency in usb_add_gadget_udc_release() interface

On Wed, 16 Aug 2017, Alexey Khoroshilov wrote:

> Hello,
> 
> usb_add_gadget_udc_release() gets release() argument that allows to
> release user resources.
> 
> As far as I can see, the release() is called on error paths 
> of usb_add_gadget_udc_release() as a result of
> put_device(&gadget->dev);
> except for the only path going via err1.
> 
> As a result a caller of the usb_add_gadget_udc_release() have no chance
> to know if the release() was invoked or not.
> 
> It may lead to memory leaks (drivers/usb/gadget/udc/snps_udc_core.c)
> or to double free (drivers/usb/gadget/udc/fsl_udc_core.c).
> 
> Is my reading correct? If so, should we always call release() on error paths?

How about this (untested)?

Alan Stern


Index: usb-4.x/drivers/usb/gadget/udc/core.c
===================================================================
--- usb-4.x.orig/drivers/usb/gadget/udc/core.c
+++ usb-4.x/drivers/usb/gadget/udc/core.c
@@ -1137,10 +1137,6 @@ int usb_add_gadget_udc_release(struct de
 	struct usb_udc		*udc;
 	int			ret = -ENOMEM;
 
-	udc = kzalloc(sizeof(*udc), GFP_KERNEL);
-	if (!udc)
-		goto err1;
-
 	dev_set_name(&gadget->dev, "gadget");
 	INIT_WORK(&gadget->work, usb_gadget_state_work);
 	gadget->dev.parent = parent;
@@ -1150,7 +1146,13 @@ int usb_add_gadget_udc_release(struct de
 	else
 		gadget->dev.release = usb_udc_nop_release;
 
-	ret = device_register(&gadget->dev);
+	device_initialize(&gadget->dev);
+
+	udc = kzalloc(sizeof(*udc), GFP_KERNEL);
+	if (!udc)
+		goto err1;
+
+	ret = device_add(&gadget->dev);
 	if (ret)
 		goto err2;
 
@@ -1197,10 +1199,10 @@ err3:
 	device_del(&gadget->dev);
 
 err2:
-	put_device(&gadget->dev);
 	kfree(udc);
 
 err1:
+	put_device(&gadget->dev);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(usb_add_gadget_udc_release);