[PATCH net v5 6/7] usbnet: ipheth: fix DPE OoB read

[Foster Snowhill <forst@pen.gy>]

Fix an out-of-bounds DPE read, limit the number of processed DPEs to
the amount that fits into the fixed-size NDP16 header.

Fixes: a2d274c62e44 ("usbnet: ipheth: add CDC NCM support")
Cc: stable@vger.kernel.org
Signed-off-by: Foster Snowhill <forst@pen.gy>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
---
v5:
    No code changes. Added Cc to stable and Reviewed-by Jakub tags.
v4: https://lore.kernel.org/netdev/20250105010121.12546-7-forst@pen.gy/
    Split from "usbnet: ipheth: refactor NCM datagram loop, fix DPE OoB
    read" in v3. This commit is responsible for addressing the potential
    OoB read.
v3: https://lore.kernel.org/netdev/20241123235432.821220-5-forst@pen.gy/
    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, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
index 03249208612e..5347cd7e295b 100644
--- a/drivers/net/usb/ipheth.c
+++ b/drivers/net/usb/ipheth.c
@@ -246,7 +246,7 @@ static int ipheth_rcvbulk_callback_ncm(struct urb *urb)
 		goto rx_error;
 
 	dpe = ncm0->dpe16;
-	while (true) {
+	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);
 
@@ -268,8 +268,6 @@ static int ipheth_rcvbulk_callback_ncm(struct urb *urb)
 		retval = ipheth_consume_skb(buf, dg_len, dev);
 		if (retval != 0)
 			return retval;
-
-		dpe++;
 	}
 
 rx_error:
-- 
2.45.1