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 <orcohen@paloaltonetworks.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
(backported from
https://patchwork.ozlabs.org/project/netdev/patch/20200904040528.3635711-1-edumazet@google.com/)
Signed-off-by: Robert Kolchmeyer <rkolchmeyer@google.com>

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/20200904040528.3635711-1-edumazet@google.com/)

Change-Id: Ifc451bdd97c124917e49023db2d7f3a0356d4801
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/5043
Tested-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Roy Yang <royyang@google.com>
(cherry picked from commit c46f8a87c479cd2e964513992d3eab92eff5c160)
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/5022
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
1 file changed