linux-kernel - [PATCH] USB: Avoid NULL pointer dereference in usb

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Message-ID: <alpine.LNX.2.00.1107111119080.4462@swampdragon.chaosbits.net>
Date:	Mon, 11 Jul 2011 11:21:18 +0200 (CEST)
From:	Jesper Juhl <jj@...osbits.net>
To:	linux-kernel@...r.kernel.org
cc:	linux-usb@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Andiry Xu <andiry.xu@....com>, Luben Tuikov <ltuikov@...oo.com>
Subject: [PATCH] USB: Avoid NULL pointer dereference in usb_disconnect()

If, in drivers/usb/core/hub.c::usb_disconnect(), 'udev' is NULL, then
we'll never get to the printing of a debug message and returning from
the function since we'll have already dereferenced the NULL pointer in
the bus_to_hcd(udev->bus) call.
This patch moves the dereference to after the test for NULL, thus
avoiding that potential crash.

Signed-off-by: Jesper Juhl <jj@...osbits.net>
---
 drivers/usb/core/hub.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

 disclaimer: compile tested only.

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index a428aa0..0a98c76 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1634,13 +1634,15 @@ void usb_disconnect(struct usb_device **pdev)
 {
 	struct usb_device	*udev = *pdev;
 	int			i;
-	struct usb_hcd		*hcd = bus_to_hcd(udev->bus);
+	struct usb_hcd		*hcd;
 
 	if (!udev) {
 		pr_debug ("%s nodev\n", __func__);
 		return;
 	}
 
+	hcd = bus_to_hcd(udev->bus);
+
 	/* mark the device as inactive, so any further urb submissions for
 	 * this device (and any of its children) will fail immediately.
 	 * this quiesces everything except pending urbs.
-- 
1.7.6


-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
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