usbnet: ipheth: use static NDP16 location in URB

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: 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.

References

• https://git.kernel.org/stable/c/8fb062178e1ce180e2cfdc9abc83a1b9fea381ca
• https://git.kernel.org/stable/c/cf1ac7f7cf601ac31d1580559c002b5e37b733b7
• https://git.kernel.org/stable/c/2b619445dcb6dab97d8ed033fb57225aca1288c4
• https://git.kernel.org/stable/c/86586dcb75cb8fd062a518aca8ee667938b91efb