ipvlan: Fix out-of-bound bugs caused by unset skb->mac_header

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

ipvlan: Fix out-of-bound bugs caused by unset skb->mac_header

If an AF_PACKET socket is used to send packets through ipvlan and the

default xmit function of the AF_PACKET socket is changed from

dev_queue_xmit() to packet_direct_xmit() via setsockopt() with the option

name of PACKET_QDISC_BYPASS, the skb->mac_header may not be reset and

remains as the initial value of 65535, this may trigger slab-out-of-bounds

bugs as following:

=================================================================

UG: KASAN: slab-out-of-bounds in ipvlan_xmit_mode_l2+0xdb/0x330 [ipvlan]

PU: 2 PID: 1768 Comm: raw_send Kdump: loaded Not tainted 6.0.0-rc4+ #6

ardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33

all Trace:

print_address_description.constprop.0+0x1d/0x160

print_report.cold+0x4f/0x112

kasan_report+0xa3/0x130

ipvlan_xmit_mode_l2+0xdb/0x330 [ipvlan]

ipvlan_start_xmit+0x29/0xa0 [ipvlan]

__dev_direct_xmit+0x2e2/0x380

packet_direct_xmit+0x22/0x60

packet_snd+0x7c9/0xc40

sock_sendmsg+0x9a/0xa0

__sys_sendto+0x18a/0x230

__x64_sys_sendto+0x74/0x90

do_syscall_64+0x3b/0x90

entry_SYSCALL_64_after_hwframe+0x63/0xcd

The root cause is:

1. packet_snd() only reset skb->mac_header when sock->type is SOCK_RAW

and skb->protocol is not specified as in packet_parse_headers()

2. packet_direct_xmit() doesn't reset skb->mac_header as dev_queue_xmit()

In this case, skb->mac_header is 65535 when ipvlan_xmit_mode_l2() is

called. So when ipvlan_xmit_mode_l2() gets mac header with eth_hdr() which

use "skb->head + skb->mac_header", out-of-bound access occurs.

This patch replaces eth_hdr() with skb_eth_hdr() in ipvlan_xmit_mode_l2()

and reset mac header in multicast to solve this out-of-bound bug.