net/packet: fix overflow in tpacket_rcv

Using tp_reserve to calculate netoff can overflow as
tp_reserve is unsigned int and netoff is unsigned short.

This may lead to macoff receving a smaller value then
sizeof(struct virtio_net_hdr), and if po->has_vnet_hdr
is set, an out-of-bounds write will occur when
calling virtio_net_hdr_from_skb.

The bug is fixed by converting netoff to unsigned int
and checking if it exceeds USHRT_MAX.

This addresses CVE-2020-14386

Fixes: 8913336a7e8d ("packet: add PACKET_RESERVE sockopt")
Signed-off-by: Or Cohen <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
(backported from
https://patchwork.ozlabs.org/project/netdev/patch/[email protected]/)
Signed-off-by: Robert Kolchmeyer <[email protected]>

BUG=b/167730744
TEST=Manually tried the reproducer before and after this fix.
RELEASE_NOTE=Fixed overflow in tpacket_rcv, which caused CVE-2020-14386.
SOURCE=FROMLIST(https://patchwork.ozlabs.org/project/netdev/patch/[email protected]/)

Change-Id: Ifc451bdd97c124917e49023db2d7f3a0356d4801
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/5043
Tested-by: Robert Kolchmeyer <[email protected]>
Reviewed-by: Roy Yang <[email protected]>
1 file changed