linux-kernel - Re: [linux-usb-devel] [PATCH] USB Pegasus driver - avoid a potential NULL pointer dereference.

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Message-ID: <alpine.LFD.0.999.0707292346150.30928@enigma.security.iitk.ac.in>
Date:	Sun, 29 Jul 2007 23:48:24 +0530 (IST)
From:	Satyam Sharma <satyam@...radead.org>
To:	Oliver Neukum <oliver@...kum.org>
cc:	linux-usb-devel@...ts.sourceforge.net,
	Jesper Juhl <jesper.juhl@...il.com>,
	Greg Kroah-Hartman <greg@...ah.com>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Petko Manolov <petkan@...rs.sourceforge.net>
Subject: Re: [linux-usb-devel] [PATCH] USB Pegasus driver - avoid a potential
 NULL pointer dereference.



On Sun, 29 Jul 2007, Oliver Neukum wrote:

> Am Sonntag 29 Juli 2007 schrieb Jesper Juhl:
> > On 29/07/07, Satyam Sharma <satyam.sharma@...il.com> wrote:
> > > Hi,
> > >
> > > On 7/29/07, Jesper Juhl <jesper.juhl@...il.com> wrote:
> > > > Hello,
> > > >
> > > > This patch makes sure we don't dereference a NULL pointer in
> > > > drivers/net/usb/pegasus.c::write_bulk_callback() in the initial
> > > > struct net_device *net = pegasus->net; assignment.
> > > > The existing code checks if 'pegasus' is NULL and bails out if
> > > > it is, so we better not touch that pointer until after that check.
> > > > [...]
> > >
> > > Is it really possible that we're called into this function with
> > > urb->context == NULL? If not, I'd suggest let's just get rid of
> > > the check itself, instead.
> > >
> > I'm not sure. I am not very familiar with this code. I just figured
> > that moving the assignment is potentially a little safer and it is
> > certainly no worse than the current code, so that's a safe and
> > potentially benneficial change. Removing the check may be safe but I'm
> > not certain enough to make that call...
> 
> pegasus == NULL there would be a kernel bug. Silently ignoring
> it, like the code now wants to do is bad. As the oops has never been
> reported, I figure turning it into an explicit debugging test is overkill,
> so removal seems to be the best option.

Ok, thanks. Updated patch below.

[PATCH] pegasus: Remove bogus checks in urb->complete() callbacks

urb->complete() callbacks registered in drivers/net/usb/pegasus.c needlessly
check for urb->context != NULL, but that is not possible (the only way that
can be possible would be a kernel bug elsewhere, and these checks would
simply end up hiding that). So let's remove the bogus checks.

Signed-off-by: Satyam Sharma <satyam@...radead.org>

---

 drivers/net/usb/pegasus.c |    9 +--------
 1 files changed, 1 insertions(+), 8 deletions(-)

diff --git a/drivers/net/usb/pegasus.c b/drivers/net/usb/pegasus.c
index a05fd97..439ef9f 100644
--- a/drivers/net/usb/pegasus.c
+++ b/drivers/net/usb/pegasus.c
@@ -770,9 +770,6 @@ static void write_bulk_callback(struct urb *urb)
 	pegasus_t *pegasus = urb->context;
 	struct net_device *net = pegasus->net;
 
-	if (!pegasus)
-		return;
-
 	if (!netif_device_present(net) || !netif_running(net))
 		return;
 
@@ -805,13 +802,9 @@ static void write_bulk_callback(struct urb *urb)
 static void intr_callback(struct urb *urb)
 {
 	pegasus_t *pegasus = urb->context;
-	struct net_device *net;
+	struct net_device *net = pegasus->net;
 	int status;
 
-	if (!pegasus)
-		return;
-	net = pegasus->net;
-
 	switch (urb->status) {
 	case 0:
 		break;
-
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