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

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Message-ID: <alpine.LNX.2.00.1101132229260.11347@swampdragon.chaosbits.net>
Date:	Thu, 13 Jan 2011 22:40:11 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	linux-kernel@...r.kernel.org
cc:	Oliver Neukum <oliver@...kum.name>,
	Greg Kroah-Hartman <gregkh@...e.de>, linux-usb@...r.kernel.org,
	netdev@...r.kernel.org,
	Alexey Orishko <alexey.orishko@...ricsson.com>,
	Hans Petter Selasky <hans.petter.selasky@...ricsson.com>
Subject: [PATCH] USB CDC NCM: Don't deref NULL in cdc_ncm_rx_fixup() and
 don't use uninitialized variable.

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@...osbits.net>
---
 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@...osbits.net>            http://www.chaosbits.net/
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