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

I have the same problem in my development..

Somewhere  in my code:

	unsigned char *data = urb->transfer_buffer ;
....
        if ( data == NULL )
	                dbg("%s - data is NULL !!!",__FUNCTION__ );

	if ( urb->actual_length == 1  && data != NULL )
		len = (int) data[0];


If I don’t do this check in a usb callback function, I have kernel panic
deference to null pointer !
But the fun stuff in this story is that I never see the debug " data is NULL
!!! " so This never happen if I do this check....


Any idea ?

Alain



-----Message d'origine-----
De : [email protected]
[mailto:[email protected]] De la part de Satyam
Sharma
Envoyé : dimanche 29 juillet 2007 20:18
À : Oliver Neukum
Cc : [email protected]; Petko Manolov; Greg
Kroah-Hartman; Jesper Juhl; Linux Kernel Mailing List;
[email protected]
Objet : 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 <[email protected]> wrote:
> > > Hi,
> > >
> > > On 7/29/07, Jesper Juhl <[email protected]> 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 <[email protected]>

---

 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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