From 8d2b1a1ec9f559d30b724877da4ce592edc41fdc Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@suse.com>
Date: Tue, 15 Feb 2022 11:35:47 +0100
Subject: [PATCH] CDC-NCM: avoid overflow in sanity checking
Git-commit: 8d2b1a1ec9f559d30b724877da4ce592edc41fdc
References: git-fixes
Patch-mainline: v5.17-rc5

A broken device may give an extreme offset like 0xFFF0
and a reasonable length for a fragment. In the sanity
check as formulated now, this will create an integer
overflow, defeating the sanity check. Both offset
and offset + len need to be checked in such a manner
that no overflow can occur.
And those quantities should be unsigned.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 drivers/net/usb/cdc_ncm.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -1474,10 +1474,10 @@ int cdc_ncm_rx_fixup(struct usbnet *dev,
 {
 	struct sk_buff *skb;
 	struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
-	int len;
+	unsigned int len;
 	int nframes;
 	int x;
-	int offset;
+	unsigned int offset;
 	struct usb_cdc_ncm_ndp16 *ndp16;
 	struct usb_cdc_ncm_dpe16 *dpe16;
 	int ndpoffset;
@@ -1517,8 +1517,8 @@ next_ndp:
 			break;
 		}
 
-		/* sanity checking */
-		if (((offset + len) > skb_in->len) ||
+		/* sanity checking - watch out for integer wrap*/
+		if ((offset > skb_in->len) || (len > skb_in->len - offset) ||
 				(len > ctx->rx_max) || (len < ETH_HLEN)) {
 			netif_dbg(dev, rx_err, dev->net,
 				  "invalid frame detected (ignored) offset[%u]=%u, length=%u, skb=%p\n",