[PATCH v2 2/2] net: usb: cdc_ncm: add ndpoffset to NDP32 nframes bounds check

[tobgaertner <tob.gaertner@me.com>]

The same bounds-check bug fixed for NDP16 in the previous patch also
exists in cdc_ncm_rx_verify_ndp32(). The DPE array size is validated
against the total skb length without accounting for ndpoffset, allowing
out-of-bounds reads when the NDP32 is placed near the end of the NTB.

Add ndpoffset to the nframes bounds check and use struct_size_t() to
express the NDP-plus-DPE-array size more clearly.

Fixes: 0fa81b304a79 ("cdc_ncm: Implement the 32-bit version of NCM Transfer Block")
Signed-off-by: Tobi Gaertner <tob.gaertner@me.com>compile-tested only.
---
 drivers/net/usb/cdc_ncm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 846f8b997..0689169d3 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -1711,8 +1711,8 @@ int cdc_ncm_rx_verify_ndp32(struct sk_buff *skb_in, int ndpoffset)
 					sizeof(struct usb_cdc_ncm_dpe32));
 	ret--; /* we process NDP entries except for the last one */
 
-	if ((sizeof(struct usb_cdc_ncm_ndp32) +
-	     ret * (sizeof(struct usb_cdc_ncm_dpe32))) > skb_in->len) {
+	if (ndpoffset + struct_size_t(struct usb_cdc_ncm_ndp32,
+				     dpe32, ret) > skb_in->len) {
 		netif_dbg(dev, rx_err, dev->net, "Invalid nframes = %d\n", ret);
 		ret = -EINVAL;
 	}
-- 
2.43.0