netdev - [PATCH net v3 4/6] usbnet: ipheth: use static NDP16 location in URB

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Message-ID: <20241123235432.821220-4-forst@pen.gy>
Date: Sun, 24 Nov 2024 00:54:30 +0100
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>,
	Oliver Neukum <oneukum@...e.com>,
	netdev@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: [PATCH net v3 4/6] usbnet: ipheth: use static NDP16 location in URB

Original code allowed for the start of NDP16 to be anywhere within the
URB based on the `wNdpIndex` value in NTH16. Only the start position of
NDP16 was checked, so it was possible for even the fixed-length part
of NDP16 to extend past the end of URB, leading to an out-of-bounds
read.

On iOS devices, the NDP16 header always directly follows NTH16. Rely on
and check for this specific format.

This, along with NCM-specific minimal URB length check that already
exists, will ensure that the fixed-length part of NDP16 plus a set
amount of DPEs fit within the URB.

Note that this commit alone does not fully address the OoB read.
The limit on the amount of DPEs needs to be enforced separately.

Fixes: a2d274c62e44 ("usbnet: ipheth: add CDC NCM support")
Signed-off-by: Foster Snowhill <forst@....gy>
---
v3:
    Split out from a monolithic patch in v2 as an atomic change.
v2: https://lore.kernel.org/netdev/20240912211817.1707844-1-forst@pen.gy/
    No code changes. Update commit message to further clarify that
    `ipheth` is not and does not aim to be a complete or spec-compliant
    CDC NCM implementation.
v1: https://lore.kernel.org/netdev/20240907230108.978355-1-forst@pen.gy/
---
 drivers/net/usb/ipheth.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
index 48c79e69bb7b..3f9ea6546720 100644
--- a/drivers/net/usb/ipheth.c
+++ b/drivers/net/usb/ipheth.c
@@ -236,16 +236,14 @@ 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) {
+	if (ncmh->dwSignature != cpu_to_le32(USB_CDC_NCM_NTH16_SIGN)) {
 		dev->net->stats.rx_errors++;
 		return retval;
 	}
 
-	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) {
+	/* 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)) {
 		dev->net->stats.rx_errors++;
 		return retval;
 	}
-- 
2.45.1