linux-kernel - [PATCH] USB: Gadget core: fix inconsistency in the interface tousb_add_gadget_udc

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Date:   Thu, 17 Aug 2017 14:49:55 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Felipe Balbi <balbi@...nel.org>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Opasiak <k.opasiak@...sung.com>,
        Anton Vasilyev <vasilyev@...ras.ru>,
        USB list <linux-usb@...r.kernel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        <ldv-project@...uxtesting.org>
Subject: [PATCH] USB: Gadget core: fix inconsistency in the interface
 tousb_add_gadget_udc_release()

The usb_add_gadget_udc_release() routine in the USB gadget core will
sometimes but not always call the gadget's release function when an
error occurs.  More specifically, if the struct usb_udc allocation
fails then the release function is not called, and for other errors it
is.

As a result, users of this routine cannot know whether they need to
deallocate the memory containing the gadget structure following an
error.  This leads to unavoidable memory leaks or double frees.

This patch fixes the problem by splitting the existing
device_register() call into device_initialize() and device_add(), and
doing the udc allocation in between.  That way, even if the allocation
fails it is still possible to call device_del(), and so the release
function will be always called following an error.

Signed-off-by: Alan Stern <stern@...land.harvard.edu>
Reported-by: Alexey Khoroshilov <khoroshilov@...ras.ru>

---


[as1837]


 drivers/usb/gadget/udc/core.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

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
@@ -1130,6 +1130,7 @@ static int check_pending_gadget_drivers(
  * @release: a gadget release function.
  *
  * Returns zero on success, negative errno otherwise.
+ * Calls the gadget release function in the latter case.
  */
 int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
 		void (*release)(struct device *dev))
@@ -1137,10 +1138,6 @@ 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 +1147,13 @@ 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 +1200,10 @@ 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);