bpf: Make remote_port field in struct bpf_sk_lookup 16-bit wide

bpf: Make remote_port field in struct bpf_sk_lookup 16-bit wide

BugLink: https://bugs.launchpad.net/bugs/1969107
commit 9a69e2b385f443f244a7e8b8bcafe5ccfb0866b4 upstream.

remote_port is another case of a BPF context field documented as a 32-bit
value in network byte order for which the BPF context access converter
generates a load of a zero-padded 16-bit integer in network byte order.

First such case was dst_port in bpf_sock which got addressed in commit
4421a582718a ("bpf: Make dst_port field in struct bpf_sock 16-bit wide").

Loading 4-bytes from the remote_port offset and converting the value with
bpf_ntohl() leads to surprising results, as the expected value is shifted
by 16 bits.

Reduce the confusion by splitting the field in two - a 16-bit field holding
a big-endian integer, and a 16-bit zero-padding anonymous field that
follows it.

Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220209184333.654927-2-jakub@cloudflare.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 0c64645e6373761f1f8f292dc122742827f1240e)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>