net: cdc_ncm: process chained NDPs

The NCM 1.0 spefication makes provisions for linking more than
one NDP into a single NTB. This is important for MBIM support,
where these NDPs might be of different types.

Following the chain of NDPs is also correct for NCM, and will
not change anything in the common case where there is only
one NDP

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/cdc_ncm.c

@@ -977,6 +977,8 @@ static int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
 	struct usb_cdc_ncm_nth16 *nth16;
 	struct usb_cdc_ncm_ndp16 *ndp16;
 	struct usb_cdc_ncm_dpe16 *dpe16;
+	int ndpoffset;
+	int loopcount = 50; /* arbitrary max preventing infinite loop */
 
 	if (ctx == NULL)
 		goto error;
@@ -1010,41 +1012,40 @@ static int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
 	}
 	ctx->rx_seq = le16_to_cpu(nth16->wSequence);
 
-	len = le16_to_cpu(nth16->wNdpIndex);
-	if ((len + sizeof(struct usb_cdc_ncm_ndp16)) > skb_in->len) {
-		pr_debug("invalid DPT16 index <%u>\n",
-					le16_to_cpu(nth16->wNdpIndex));
+	ndpoffset = le16_to_cpu(nth16->wNdpIndex);
+next_ndp:
+	if ((ndpoffset + sizeof(struct usb_cdc_ncm_ndp16)) > skb_in->len) {
+		pr_debug("invalid NDP offset  <%u>\n", ndpoffset);
 		goto error;
 	}
-
-	ndp16 = (struct usb_cdc_ncm_ndp16 *)(((u8 *)skb_in->data) + len);
+	ndp16 = (struct usb_cdc_ncm_ndp16 *)(skb_in->data + ndpoffset);
 
 	if (le32_to_cpu(ndp16->dwSignature) != USB_CDC_NCM_NDP16_NOCRC_SIGN) {
 		pr_debug("invalid DPT16 signature <%u>\n",
 					le32_to_cpu(ndp16->dwSignature));
-		goto error;
+		goto err_ndp;
 	}
 
 	if (le16_to_cpu(ndp16->wLength) < USB_CDC_NCM_NDP16_LENGTH_MIN) {
 		pr_debug("invalid DPT16 length <%u>\n",
 					le32_to_cpu(ndp16->dwSignature));
-		goto error;
+		goto err_ndp;
 	}
 
 	nframes = ((le16_to_cpu(ndp16->wLength) -
 					sizeof(struct usb_cdc_ncm_ndp16)) /
 					sizeof(struct usb_cdc_ncm_dpe16));
 	nframes--; /* we process NDP entries except for the last one */
 
-	len += sizeof(struct usb_cdc_ncm_ndp16);
+	ndpoffset += sizeof(struct usb_cdc_ncm_ndp16);
 
-	if ((len + nframes * (sizeof(struct usb_cdc_ncm_dpe16))) >
+	if ((ndpoffset + nframes * (sizeof(struct usb_cdc_ncm_dpe16))) >
 								skb_in->len) {
 		pr_debug("Invalid nframes = %d\n", nframes);
-		goto error;
+		goto err_ndp;
 	}
 
-	dpe16 = (struct usb_cdc_ncm_dpe16 *)(((u8 *)skb_in->data) + len);
+	dpe16 = (struct usb_cdc_ncm_dpe16 *)(skb_in->data + ndpoffset);
 
 	for (x = 0; x < nframes; x++, dpe16++) {
 		offset = le16_to_cpu(dpe16->wDatagramIndex);
@@ -1056,7 +1057,7 @@ static int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
 		 */
 		if ((offset == 0) || (len == 0)) {
 			if (!x)
-				goto error; /* empty NTB */
+				goto err_ndp; /* empty NTB */
 			break;
 		}
 
@@ -1067,7 +1068,7 @@ static int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
 					"offset[%u]=%u, length=%u, skb=%p\n",
 					x, offset, len, skb_in);
 			if (!x)
-				goto error;
+				goto err_ndp;
 			break;
 
 		} else {
@@ -1080,6 +1081,12 @@ static int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
 			usbnet_skb_return(dev, skb);
 		}
 	}
+err_ndp:
+	/* are there more NDPs to process? */
+	ndpoffset = le16_to_cpu(ndp16->wNextNdpIndex);
+	if (ndpoffset && loopcount--)
+		goto next_ndp;
+
 	return 1;
 error:
 	return 0;