USB: gadget: f_ncm: add bounds checks to ncm_unwrap_ntb()

Some values extracted by ncm_unwrap_ntb() could possibly lead to several
different out of bounds reads of memory.  Specifically the values passed
to netdev_alloc_skb_ip_align() need to be checked so that memory is not
overflowed.

Resolve this by applying bounds checking to a number of different
indexes and lengths of the structure parsing logic.
Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: Brooke Basile <brookebasile@gmail.com>
Acked-by: Felipe Balbi <balbi@kernel.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_ncm.c

@@ -1181,12 +1181,15 @@ static int ncm_unwrap_ntb(struct gether *port,
 	int		ndp_index;
 	unsigned	dg_len, dg_len2;
 	unsigned	ndp_len;
+	unsigned	block_len;
 	struct sk_buff	*skb2;
 	int		ret = -EINVAL;
-	unsigned	max_size = le32_to_cpu(ntb_parameters.dwNtbOutMaxSize);
+	unsigned	ntb_max = le32_to_cpu(ntb_parameters.dwNtbOutMaxSize);
+	unsigned	frame_max = le16_to_cpu(ecm_desc.wMaxSegmentSize);
 	const struct ndp_parser_opts *opts = ncm->parser_opts;
 	unsigned	crc_len = ncm->is_crc ? sizeof(uint32_t) : 0;
 	int		dgram_counter;
+	bool		ndp_after_header;
 
 	/* dwSignature */
 	if (get_unaligned_le32(tmp) != opts->nth_sign) {
@@ -1205,25 +1208,37 @@ static int ncm_unwrap_ntb(struct gether *port,
 	}
 	tmp++; /* skip wSequence */
 
+	block_len = get_ncm(&tmp, opts->block_length);
 	/* (d)wBlockLength */
-	if (get_ncm(&tmp, opts->block_length) > max_size) {
+	if (block_len > ntb_max) {
 		INFO(port->func.config->cdev, "OUT size exceeded\n");
 		goto err;
 	}
 
 	ndp_index = get_ncm(&tmp, opts->ndp_index);
+	ndp_after_header = false;
 
 	/* Run through all the NDP's in the NTB */
 	do {
-		/* NCM 3.2 */
-		if (((ndp_index % 4) != 0) &&
-				(ndp_index < opts->nth_size)) {
+		/*
+		 * NCM 3.2
+		 * dwNdpIndex
+		 */
+		if (((ndp_index % 4) != 0) ||
+				(ndp_index < opts->nth_size) ||
+				(ndp_index > (block_len -
+					      opts->ndp_size))) {
 			INFO(port->func.config->cdev, "Bad index: %#X\n",
 			     ndp_index);
 			goto err;
 		}
+		if (ndp_index == opts->nth_size)
+			ndp_after_header = true;
 
-		/* walk through NDP */
+		/*
+		 * walk through NDP
+		 * dwSignature
+		 */
 		tmp = (void *)(skb->data + ndp_index);
 		if (get_unaligned_le32(tmp) != ncm->ndp_sign) {
 			INFO(port->func.config->cdev, "Wrong NDP SIGN\n");
@@ -1234,14 +1249,15 @@ static int ncm_unwrap_ntb(struct gether *port,
 		ndp_len = get_unaligned_le16(tmp++);
 		/*
 		 * NCM 3.3.1
+		 * wLength
 		 * entry is 2 items
 		 * item size is 16/32 bits, opts->dgram_item_len * 2 bytes
 		 * minimal: struct usb_cdc_ncm_ndpX + normal entry + zero entry
 		 * Each entry is a dgram index and a dgram length.
 		 */
 		if ((ndp_len < opts->ndp_size
-				+ 2 * 2 * (opts->dgram_item_len * 2))
-				|| (ndp_len % opts->ndplen_align != 0)) {
+				+ 2 * 2 * (opts->dgram_item_len * 2)) ||
+				(ndp_len % opts->ndplen_align != 0)) {
 			INFO(port->func.config->cdev, "Bad NDP length: %#X\n",
 			     ndp_len);
 			goto err;
@@ -1258,8 +1274,21 @@ static int ncm_unwrap_ntb(struct gether *port,
 
 		do {
 			index = index2;
+			/* wDatagramIndex[0] */
+			if ((index < opts->nth_size) ||
+					(index > block_len - opts->dpe_size)) {
+				INFO(port->func.config->cdev,
+				     "Bad index: %#X\n", index);
+				goto err;
+			}
+
 			dg_len = dg_len2;
-			if (dg_len < 14 + crc_len) { /* ethernet hdr + crc */
+			/*
+			 * wDatagramLength[0]
+			 * ethernet hdr + crc or larger than max frame size
+			 */
+			if ((dg_len < 14 + crc_len) ||
+					(dg_len > frame_max)) {
 				INFO(port->func.config->cdev,
 				     "Bad dgram length: %#X\n", dg_len);
 				goto err;
@@ -1283,6 +1312,37 @@ static int ncm_unwrap_ntb(struct gether *port,
 			index2 = get_ncm(&tmp, opts->dgram_item_len);
 			dg_len2 = get_ncm(&tmp, opts->dgram_item_len);
 
+			if (index2 == 0 || dg_len2 == 0)
+				break;
+
+			/* wDatagramIndex[1] */
+			if (ndp_after_header) {
+				if (index2 < opts->nth_size + opts->ndp_size) {
+					INFO(port->func.config->cdev,
+					     "Bad index: %#X\n", index2);
+					goto err;
+				}
+			} else {
+				if (index2 < opts->nth_size + opts->dpe_size) {
+					INFO(port->func.config->cdev,
+					     "Bad index: %#X\n", index2);
+					goto err;
+				}
+			}
+			if (index2 > block_len - opts->dpe_size) {
+				INFO(port->func.config->cdev,
+				     "Bad index: %#X\n", index2);
+				goto err;
+			}
+
+			/* wDatagramLength[1] */
+			if ((dg_len2 < 14 + crc_len) ||
+					(dg_len2 > frame_max)) {
+				INFO(port->func.config->cdev,
+				     "Bad dgram length: %#X\n", dg_len);
+				goto err;
+			}
+
 			/*
 			 * Copy the data into a new skb.
 			 * This ensures the truesize is correct
@@ -1299,9 +1359,6 @@ static int ncm_unwrap_ntb(struct gether *port,
 			ndp_len -= 2 * (opts->dgram_item_len * 2);
 
 			dgram_counter++;
-
-			if (index2 == 0 || dg_len2 == 0)
-				break;
 		} while (ndp_len > 2 * (opts->dgram_item_len * 2));
 	} while (ndp_index);