netdev - [PATCH net-next] usbnet: ipheth: prevent OoB reads of NDP16

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Message-ID: <20240907230108.978355-1-forst@pen.gy>
Date: Sun,  8 Sep 2024 01:01:08 +0200
From: Foster Snowhill <forst@....gy>
To: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Georgi Valkov <gvalkov@...il.com>,
	Simon Horman <horms@...nel.org>,
	netdev@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: [PATCH net-next] usbnet: ipheth: prevent OoB reads of NDP16

There were a few potential out of bounds reads when processing
malformed URBs received from a connected device in NCM mode:

* Only the start of NDP16 (wNdpIndex) was checked to fit in the URB
  buffer.
* Datagram length check as part of DPEs could overflow.
* DPEs could be read past the end of NDP16 and even end of URB buffer
  if a trailer DPE wasn't encountered.

The above is not expected to happen in normal device operation.

To address the above issues without reimplementing more of CDC NCM,
rely on and check for a specific fixed format of incoming URBs
expected from an iOS device:

* 12-byte NTH16
* 96-byte NDP16, allowing up to 22 DPEs (up to 21 datagrams + trailer)

On iOS, NDP16 directly follows NTH16, and its length is constant
regardless of the DPE count.

Adapt the driver to use the fixed URB format. Set an upper bound for
the DPE count based on the expected header size. Always expect a null
trailer DPE.

The minimal URB length of 108 bytes (IPHETH_NCM_HEADER_SIZE) in NCM mode
is already enforced in ipheth since introduction of NCM support.

Signed-off-by: Foster Snowhill <forst@....gy>
Tested-by: Georgi Valkov <gvalkov@...il.com>
---
This should perhaps go into "net" rather than "net-next"? I submitted
the previous patch series to "net-next", but it got merged into "net"
[1]. However it's quite late in the 6.11-rc cycle, I see that 6.11-rc7
net stuff was already merged into Linus' tree ~two days ago.

[1]: https://lore.kernel.org/netdev/172320844026.3782387.2037318141249570355.git-patchwork-notify@kernel.org/
---
 drivers/net/usb/ipheth.c | 64 ++++++++++++++++++++++------------------
 1 file changed, 36 insertions(+), 28 deletions(-)

diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
index 46afb95ffabe..8c62501f47a9 100644
--- a/drivers/net/usb/ipheth.c
+++ b/drivers/net/usb/ipheth.c
@@ -61,7 +61,16 @@
 #define IPHETH_USBINTF_PROTO    1
 
 #define IPHETH_IP_ALIGN		2	/* padding at front of URB */
-#define IPHETH_NCM_HEADER_SIZE  (12 + 96) /* NCMH + NCM0 */
+/* On iOS devices, NCM headers in RX have a fixed size:
+ * - NTH16 (NCMH): 12 bytes, as per CDC NCM 1.0 spec
+ * - NDP16 (NCM0): 96 bytes
+ */
+#define IPHETH_NDP16_HEADER_SIZE 96
+#define IPHETH_NDP16_MAX_DPE	((IPHETH_NDP16_HEADER_SIZE - \
+				  sizeof(struct usb_cdc_ncm_ndp16)) / \
+				 sizeof(struct usb_cdc_ncm_dpe16))
+#define IPHETH_NCM_HEADER_SIZE	(sizeof(struct usb_cdc_ncm_nth16) + \
+				 IPHETH_NDP16_HEADER_SIZE)
 #define IPHETH_TX_BUF_SIZE      ETH_FRAME_LEN
 #define IPHETH_RX_BUF_SIZE_LEGACY (IPHETH_IP_ALIGN + ETH_FRAME_LEN)
 #define IPHETH_RX_BUF_SIZE_NCM	65536
@@ -213,9 +222,9 @@ static int ipheth_rcvbulk_callback_ncm(struct urb *urb)
 	struct usb_cdc_ncm_ndp16 *ncm0;
 	struct usb_cdc_ncm_dpe16 *dpe;
 	struct ipheth_device *dev;
+	u16 dg_idx, dg_len;
 	int retval = -EINVAL;
 	char *buf;
-	int len;
 
 	dev = urb->context;
 
@@ -225,41 +234,40 @@ static int ipheth_rcvbulk_callback_ncm(struct urb *urb)
 	}
 
 	ncmh = urb->transfer_buffer;
-	if (ncmh->dwSignature != cpu_to_le32(USB_CDC_NCM_NTH16_SIGN) ||
-	    le16_to_cpu(ncmh->wNdpIndex) >= urb->actual_length) {
-		dev->net->stats.rx_errors++;
-		return retval;
-	}
+	if (ncmh->dwSignature != cpu_to_le32(USB_CDC_NCM_NTH16_SIGN))
+		goto rx_error;
 
-	ncm0 = urb->transfer_buffer + le16_to_cpu(ncmh->wNdpIndex);
-	if (ncm0->dwSignature != cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN) ||
-	    le16_to_cpu(ncmh->wHeaderLength) + le16_to_cpu(ncm0->wLength) >=
-	    urb->actual_length) {
-		dev->net->stats.rx_errors++;
-		return retval;
-	}
+	/* On iOS, NDP16 directly follows NTH16 */
+	ncm0 = urb->transfer_buffer + sizeof(struct usb_cdc_ncm_nth16);
+	if (ncm0->dwSignature != cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN))
+		goto rx_error;
 
 	dpe = ncm0->dpe16;
-	while (le16_to_cpu(dpe->wDatagramIndex) != 0 &&
-	       le16_to_cpu(dpe->wDatagramLength) != 0) {
-		if (le16_to_cpu(dpe->wDatagramIndex) >= urb->actual_length ||
-		    le16_to_cpu(dpe->wDatagramIndex) +
-		    le16_to_cpu(dpe->wDatagramLength) > urb->actual_length) {
-			dev->net->stats.rx_length_errors++;
-			return retval;
-		}
+	for (int dpe_i = 0; dpe_i < IPHETH_NDP16_MAX_DPE; ++dpe_i, ++dpe) {
+		dg_idx = le16_to_cpu(dpe->wDatagramIndex);
+		dg_len = le16_to_cpu(dpe->wDatagramLength);
+
+		/* Null DPE must be present after last datagram pointer entry
+		 * (3.3.1 USB CDC NCM spec v1.0)
+		 */
+		if (dg_idx == 0 && dg_len == 0)
+			return 0;
+
+		if (dg_idx < IPHETH_NCM_HEADER_SIZE ||
+		    dg_idx >= urb->actual_length ||
+		    dg_len > urb->actual_length - dg_idx)
+			goto rx_error;
 
-		buf = urb->transfer_buffer + le16_to_cpu(dpe->wDatagramIndex);
-		len = le16_to_cpu(dpe->wDatagramLength);
+		buf = urb->transfer_buffer + dg_idx;
 
-		retval = ipheth_consume_skb(buf, len, dev);
+		retval = ipheth_consume_skb(buf, dg_len, dev);
 		if (retval != 0)
 			return retval;
-
-		dpe++;
 	}
 
-	return 0;
+rx_error:
+	dev->net->stats.rx_errors++;
+	return retval;
 }
 
 static void ipheth_rcvbulk_callback(struct urb *urb)
-- 
2.45.1