[PATCH] USB CDC NCM: Don't deref NULL in cdc_ncm_rx_fixup() and don't use uninitialized variable.

[PATCH] USB CDC NCM: Don't deref NULL in cdc_ncm_rx_fixup() and don't use uninitialized variable.

[Jesper Juhl]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1831 bytes --]

skb_clone() dynamically allocates memory and may fail. If it does it 
returns NULL. This means we'll dereference a NULL pointer in 
drivers/net/usb/cdc_ncm.c::cdc_ncm_rx_fixup().
As far as I can tell, the proper way to deal with this is simply to goto 
the error label.

Furthermore gcc complains that 'skb' may be used uninitialized:
  drivers/net/usb/cdc_ncm.c: In function ‘cdc_ncm_rx_fixup’:
  drivers/net/usb/cdc_ncm.c:922:18: warning: ‘skb’ may be used uninitialized in this function
and I believe it is right. On the line where we
  pr_debug("invalid frame detected (ignored)" ...
we are using the local variable 'skb' but nothing has ever been assigned 
to that variable yet. I believe the correct fix for that is to use 
'skb_in' instead.

Signed-off-by: Jesper Juhl <jj-IYz4IdjRLj0sV2N9l4h3zg@public.gmane.org>
---
 cdc_ncm.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

  compile tested only.

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 593c104..d776c4a 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -1021,13 +1021,15 @@ static int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
 		    (temp > CDC_NCM_MAX_DATAGRAM_SIZE) || (temp < ETH_HLEN)) {
 			pr_debug("invalid frame detected (ignored)"
 				"offset[%u]=%u, length=%u, skb=%p\n",
-							x, offset, temp, skb);
+							x, offset, temp, skb_in);
 			if (!x)
 				goto error;
 			break;
 
 		} else {
 			skb = skb_clone(skb_in, GFP_ATOMIC);
+			if (!skb)
+				goto error;
 			skb->len = temp;
 			skb->data = ((u8 *)skb_in->data) + offset;
 			skb_set_tail_pointer(skb, temp);



-- 
Jesper Juhl <jj-IYz4IdjRLj0sV2N9l4h3zg@public.gmane.org>            http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.

Re: [PATCH] USB CDC NCM: Don't deref NULL in cdc_ncm_rx_fixup() and don't use uninitialized variable.

[David Miller]

From: Jesper Juhl <jj@chaosbits.net>
Date: Thu, 13 Jan 2011 22:40:11 +0100 (CET)

> skb_clone() dynamically allocates memory and may fail. If it does it 
> returns NULL. This means we'll dereference a NULL pointer in 
> drivers/net/usb/cdc_ncm.c::cdc_ncm_rx_fixup().
> As far as I can tell, the proper way to deal with this is simply to goto 
> the error label.
> 
> Furthermore gcc complains that 'skb' may be used uninitialized:
>   drivers/net/usb/cdc_ncm.c: In function ‘cdc_ncm_rx_fixup’:
>   drivers/net/usb/cdc_ncm.c:922:18: warning: ‘skb’ may be used uninitialized in this function
> and I believe it is right. On the line where we
>   pr_debug("invalid frame detected (ignored)" ...
> we are using the local variable 'skb' but nothing has ever been assigned 
> to that variable yet. I believe the correct fix for that is to use 
> 'skb_in' instead.
> 
> Signed-off-by: Jesper Juhl <jj@chaosbits.net>

Applied.