Date: Mon, 20 Aug 2018 21:59:14 +0700 From: Eugene Grosbein <eugen@grosbein.net> To: Stefan Bethke <stb@lassitu.de>, FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: Bind to port <1024 in jail Message-ID: <6bfc8608-946d-39eb-cc57-88b3dc3bd7c5@grosbein.net> In-Reply-To: <75536186-7D58-498C-BFC6-9284EB7CB444@lassitu.de> References: <75536186-7D58-498C-BFC6-9284EB7CB444@lassitu.de>
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20.08.2018 21:47, Stefan Bethke wrote: > I have a Go program (acme-dns) that wants to bind 53, 80, and 443, and I’d rather have it run as a non-privileged user. The program doesn’t provide a facility to drop privs after binding the ports. I’m planning to run it in a jail. > > After some googling, it appears that a couple of years ago I should have been able to do: > sysctl net.inet.ip.portrange.reservedhigh=0 > and allow all processes to bind to „low“ ports. This does not work in my jails on a 11-stable host. > > $ sudo sysctl net.inet.ip.portrange.reservedhigh=0 > net.inet.ip.portrange.reservedhigh: 1023 > sysctl: net.inet.ip.portrange.reservedhigh=0: Operation not permitted > > Securelevel should not interfere: > $ sysctl kern.securelevel > kern.securelevel: -1 > > Is there a way to allow regular processes to bind to low ports? Yes. Just use mac_portacl kernel module: kldload mac_portacl Once loaded, it duplicates net.inet.ip.portrange.reservedhigh protection with its own security.mac.portacl.port_high, so it's safe to disable "reservedhigh" for whole system by running sysctl net.inet.ip.portrange.reservedhigh=0 for host. The trick is that mac_portacl provides a way to selectively give permission for non-root UID to bind low ports: security.mac.portacl.rules=uid:88:tcp:80,uid:88:tcp:443,uid:53:tcp:53,uid:53:udp:53 It works just fine for a host and I use it for name servers utilizing port 53 for a box with dynamically created interfaces, so it may bind the port for distinct IP addresses after it dropped privilegies when new interface is created and get new IP assigned. I have not tried it for a jails, though. Please try and respond.
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