linux-kernel - Re: [PATCH 2/2] Eliminate double kfree

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Date:	Thu, 29 May 2008 11:33:39 -0400
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Julia Lawall <julia@...u.dk>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 2/2] Eliminate double kfree

Hi Julia,

On Thu, May 29, 2008 at 03:05:07PM +0200, Julia Lawall wrote:
> From: Julia Lawall <julia@...u.dk>
> 
> The variable report is only non-NULL and non-freed in a small region of
> code, so it should only be freed in error handling code that comes from
> that region.
> 

Thank you for your patch. There isn't a double-kfree though, as far
as I can see. Because we need to free the report in both success and
failure cases the error handling is a bit unwieldy I agree. I don't
want to apply your patch though because I don't like when we bypass
parts of error handling path that weren't bypassed if we aborted
earlier, if you follow me.

What do you think about the patch below?

-- 
Dmitry

Input: gtco - clean up error handling in gtco_probe

Thanks to Julia Lawall for noticing ugliness.

Signed-off-by: Dmitry Torokhov <dtor@...l.ru>
---
 drivers/input/tablet/gtco.c |   17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

Index: linux/drivers/input/tablet/gtco.c
===================================================================
--- linux.orig/drivers/input/tablet/gtco.c
+++ linux/drivers/input/tablet/gtco.c
@@ -830,7 +830,7 @@ static int gtco_probe(struct usb_interfa
 	struct gtco             *gtco;
 	struct input_dev        *input_dev;
 	struct hid_descriptor   *hid_desc;
-	char                    *report = NULL;
+	char                    *report;
 	int                     result = 0, retry;
 	int			error;
 	struct usb_endpoint_descriptor *endpoint;
@@ -916,12 +916,16 @@ static int gtco_probe(struct usb_interfa
 					 le16_to_cpu(hid_desc->wDescriptorLength),
 					 5000); /* 5 secs */
 
-		if (result == le16_to_cpu(hid_desc->wDescriptorLength))
+		dbg("usb_control_msg result: %d", result);
+		if (result == le16_to_cpu(hid_desc->wDescriptorLength)) {
+			parse_hid_report_descriptor(gtco, report, result);
 			break;
+		}
 	}
 
+	kfree(report);
+
 	/* If we didn't get the report, fail */
-	dbg("usb_control_msg result: :%d", result);
 	if (result != le16_to_cpu(hid_desc->wDescriptorLength)) {
 		err("Failed to get HID Report Descriptor of size: %d",
 		    hid_desc->wDescriptorLength);
@@ -929,12 +933,6 @@ static int gtco_probe(struct usb_interfa
 		goto err_free_urb;
 	}
 
-	/* Now we parse the report */
-	parse_hid_report_descriptor(gtco, report, result);
-
-	/* Now we delete it */
-	kfree(report);
-
 	/* Create a device file node */
 	usb_make_path(gtco->usbdev, gtco->usbpath, sizeof(gtco->usbpath));
 	strlcat(gtco->usbpath, "/input0", sizeof(gtco->usbpath));
@@ -988,7 +986,6 @@ static int gtco_probe(struct usb_interfa
 	usb_buffer_free(gtco->usbdev, REPORT_MAX_SIZE,
 			gtco->buffer, gtco->buf_dma);
  err_free_devs:
-	kfree(report);
 	input_free_device(input_dev);
 	kfree(gtco);
 	return error;
--
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