Description: net/packet: fix overflow in tpacket_rcv
References:
 https://www.openwall.com/lists/oss-security/2020/09/03/3
Notes:
 carnil> To create AF_PACKET sockets one needs CAP_NET_RAW in the
 carnil> network namepsace, which could be aquired by unprivileged
 carnil> processes on systems where unprivileged namespaces are enabled.
 carnil> Debian does not enable those.
Bugs:
upstream: needed
4.19-upstream-stable: needed
4.9-upstream-stable: needed
sid: needed
4.19-buster-security: needed
4.9-stretch-security: needed