linux-kernel - [PATCH 5.15 026/139] CDC-NCM: avoid overflow in sanity checking

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Message-Id: <20220228172350.528117345@linuxfoundation.org>
Date:   Mon, 28 Feb 2022 18:23:20 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Oliver Neukum <oneukum@...e.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 5.15 026/139] CDC-NCM: avoid overflow in sanity checking

From: Oliver Neukum <oneukum@...e.com>

commit 8d2b1a1ec9f559d30b724877da4ce592edc41fdc upstream.

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@...e.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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
@@ -1715,10 +1715,10 @@ 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;
 	union {
 		struct usb_cdc_ncm_ndp16 *ndp16;
 		struct usb_cdc_ncm_ndp32 *ndp32;
@@ -1790,8 +1790,8 @@ 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",