tree fb9b89044fc29512c4bc74647183c6323c2b854e
parent 5fd498f32134f8369936c2b35550f3d092be3421
author Ghanan Gowripalan <ghanan@google.com> 1616518497 -0700
committer gVisor bot <gvisor-bot@google.com> 1616518621 -0700

Explicitly allow martian loopback packets

...instead of opting out of them.

Loopback traffic should be stack-local but gVisor has some clients
that depend on the ability to receive loopback traffic that originated
from outside of the stack. Because of this, we guard this change behind
IP protocol options.

A previous change provided the facility to deny these martian loopback
packets but this change requires client to opt-in to accepting martian
loopback packets as accepting martian loopback packets are not meant
to be accepted, as per RFC 1122 section 3.2.1.3.g:

        (g)  { 127, <any> }

             Internal host loopback address.  Addresses of this form
             MUST NOT appear outside a host.

PiperOrigin-RevId: 364581174