packet: validate address length

Packet sockets with SOCK_DGRAM may pass an address for use in
dev_hard_header. Ensure that it is of sufficient length.
Reported-by: Nsyzbot <syzkaller@googlegroups.com>
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -2627,6 +2627,8 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		proto	= saddr->sll_protocol;
 		addr	= saddr->sll_addr;
 		dev = dev_get_by_index(sock_net(&po->sk), saddr->sll_ifindex);
+		if (addr && dev && saddr->sll_halen < dev->addr_len)
+			goto out;
 	}
 
 	err = -ENXIO;
@@ -2825,6 +2827,8 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 		proto	= saddr->sll_protocol;
 		addr	= saddr->sll_addr;
 		dev = dev_get_by_index(sock_net(sk), saddr->sll_ifindex);
+		if (addr && dev && saddr->sll_halen < dev->addr_len)
+			goto out;
 	}
 
 	err = -ENXIO;