net: usb: ax88179_178a: Fix out-of-bounds accesses in RX fixup

ax88179_rx_fixup() contains several out-of-bounds accesses that can be
triggered by a malicious (or defective) USB device, in particular:

 - The metadata array (hdr_off..hdr_off+2*pkt_cnt) can be out of bounds,
   causing OOB reads and (on big-endian systems) OOB endianness flips.
 - A packet can overlap the metadata array, causing a later OOB
   endianness flip to corrupt data used by a cloned SKB that has already
   been handed off into the network stack.
 - A packet SKB can be constructed whose tail is far beyond its end,
   causing out-of-bounds heap data to be considered part of the SKB's
   data.

I have tested that this can be used by a malicious USB device to send a
bogus ICMPv6 Echo Request and receive an ICMPv6 Echo Reply in response
that contains random kernel heap data.
It's probably also possible to get OOB writes from this on a
little-endian system somehow - maybe by triggering skb_cow() via IP
options processing -, but I haven't tested that.

Fixes: e2ca90c2

 ("ax88179_178a: ASIX AX88179_178A USB 3.0/2.0 to gigabit ethernet adapter driver")
Cc: stable@kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>