syslogd: Open forwarding socket descriptors

[jfree]

Summary

Previously, when forwarding a message to a remote address, the target's
addrinfo was saved at config-parse-time. When message-deliver-time came,
the message's addrinfo was passed into sendmsg(2) and delivered by the
first available inet socket.

The use of sendmsg(2) is prohibited in Capsicum capability mode, so
sockets are now opened and connected to their remote peers at
config-parse-time when executing outside of the capability sandbox.

These sockets are then used with send(2), allowing forwarding to be
performed inside of the capability sandbox.

[markj]

This looks good to me, thanks. A couple of minor nits.

usr.sbin/syslogd/syslogd.c

367

Hopefully f->f_addr_fds == NULL implies f->f_num_addr_fds == 0, in which case there's no need to check this condition explicitly.

3051

It'd be nicer to use calloc() here IMO.

[jfree]

Address Mark's comments: use calloc() instead of malloc() for
memory allocations. This is done to avoid potential integer overflow
in total allocation size.

[jfree]

usr.sbin/syslogd/syslogd.c

367

Yes. f->f_addr_fds == NULL does imply f->f_num_addr_fds == 0

[markj]

usr.sbin/syslogd/syslogd_cap_config.c

218

Same here, it'd be nice to use calloc().