privsep: Enable Capsicum for all processes.

Except for the priviledged process.
This is quite an in-depth change:
 * ARP is now one process per address
 * BPF flags are now returned via privsep
 * BPF write filters are locked when supported
 * The root process sends to the network

The last step is done by opening RAW sockets and then sending a UDP
header (where applicable) to avoid binding to an address
which is already in use by the reader sockets.

This is slightly wasteful for OS's without sandboxing but does
have the very nice side effect of not needing a source address
to unicast DHCPs replies from which makes the code smaller.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/if.h b/src/if.h
index 73f8b915..23d94914 100644
--- a/src/if.h
+++ b/src/if.h
@@ -210,6 +210,9 @@ int if_setmac(struct interface *ifp, void *, uint8_t);
 #else
 # define SOCK_NONBLOCK	0x20000000
 #endif
+#ifndef SOCK_CXNB
+#define	SOCK_CXNB	SOCK_CLOEXEC | SOCK_NONBLOCK
+#endif
 
 int if_route(unsigned char, const struct rt *rt);
 int if_initrt(struct dhcpcd_ctx *, rb_tree_t *, int);