extensions: xt_socket: add txlate support for socket match

v2: document the match semantics of -m socket.

Ignore --nowildcard if used with other options when translating
and add "wildcard 0" if the option is missing.

"-m socket" will ignore sockets bound to 0.0.0.0/:: by default,
unless --nowildcard is given.

So, xlate must always append "wildcard 0", can elide "wildcard"
if other options are present along with --nowildcard.

To emulate "-m socket --nowildcard", check for "wildcard <= 1" to
get a "socket exists" type matching.

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Phil Sutter <phil@nwl.cc>

1 files changed, 17 insertions, 0 deletions

diff --git a/extensions/libxt_socket.txlate b/extensions/libxt_socket.txlate
new file mode 100644
index 00000000..7731e42e
--- /dev/null
+++ b/extensions/libxt_socket.txlate
@@ -0,0 +1,17 @@
+# old socket match, no options.  Matches if sk can be found and it is not bound to 0.0.0.0/::
+iptables-translate -A INPUT -m socket
+nft 'add rule ip filter INPUT socket wildcard 0 counter'
+
+iptables-translate -A INPUT -m socket --transparent
+nft 'add rule ip filter INPUT socket wildcard 0 socket transparent 1 counter'
+
+# Matches if sk can be found.  Doesn't matter as to what addess it is bound to.
+# therefore, emulate "exists".
+iptables-translate -A INPUT -m socket --nowildcard
+nft 'add rule ip filter INPUT socket wildcard le 1 counter'
+
+iptables-translate -A INPUT -m socket --restore-skmark
+nft 'add rule ip filter INPUT socket wildcard 0 meta mark set socket mark counter'
+
+iptables-translate -A INPUT -m socket --transparent --nowildcard --restore-skmark
+nft 'add rule ip filter INPUT socket transparent 1 meta mark set socket mark counter'