netdev - [PATCH net v3 2/6] usbnet: ipheth: fix possible overflow in DPE length check

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Message-ID: <20241123235432.821220-2-forst@pen.gy>
Date: Sun, 24 Nov 2024 00:54:28 +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 2/6] usbnet: ipheth: fix possible overflow in DPE length check

Originally, it was possible for the DPE length check to overflow if
wDatagramIndex + wDatagramLength > U16_MAX. This could lead to an OoB
read.

Move the wDatagramIndex term to the other side of the inequality.

An existing condition ensures that wDatagramIndex < urb->actual_length.

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 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
index 2084b940b4ea..4b590a5269fd 100644
--- a/drivers/net/usb/ipheth.c
+++ b/drivers/net/usb/ipheth.c
@@ -254,8 +254,8 @@ static int ipheth_rcvbulk_callback_ncm(struct urb *urb)
 	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) {
+		    le16_to_cpu(dpe->wDatagramLength) > urb->actual_length -
+		    le16_to_cpu(dpe->wDatagramIndex)) {
 			dev->net->stats.rx_length_errors++;
 			return retval;
 		}
-- 
2.45.1