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")
Cc: stable@vger.kernel.org
Signed-off-by: Foster Snowhill <forst@pen.gy>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c
index 46afb95ffabe3b0075fdf9782af9803610d43016..45daae234cb856d921f66d53494983c44999daee 100644 (file)
--- a/drivers/net/usb/ipheth.c
+++ b/drivers/net/usb/ipheth.c
@@ -243,8 +243,8 @@ 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;
                }