Debugging why ping was Broken in Docker Images(cyphar.com) |
Debugging why ping was Broken in Docker Images(cyphar.com) |
...no. Privileged ports are a way to prevent an unprivileged user from turning a service crash into a service takeover.
Windows Firewall seems to sort of mitigate this by only permitting a given program to communicate on a port, but -from what my testing revealed- it does not prevent other programs from _binding_ to that port. So, I strongly suspect that on Windows systems, an unprivileged user can turn a service crash into a service DoS by racing to bind to the service's port.
Whilst privileged ports are indeed used for that purpose, that doesn't mean they aren't a wart.
There's no necessary technical reason why unprivileged users can't bind to port 80, except that the designers of the network API decided to equate successfully binding to a port with having permission to receive connection requests for that port.
This leads to unpleasant situations like a web server having to run as root, even if (usually) only temporarily, solely because it needs to bind port 80.
This makes less sense especially with Docker, since even if a containerized web server binds to port 80, it won't receive connections from the outside world unless the container is configured to forward the "real" port 80 to it.
not on modern linux. see CAP_NET_BIND_SERVICE in `man 7 capabilities`.
I agree that there are situations that not-infrequently arise that require additional IP port access restrictions. However, do you agree that removing the notion of privileged ports [0] would
1) Not give you the more-fine grained access restrictions that you're looking for
2) Actually weaken security on Linux systems
? (Additionally, GRSecurity, SELinux, and -apparently- AppArmor all appear to provide the finer-grained control that you're looking for. There is also this [1] which lets you do something like what Windows Firewall does and use iptables to restrict which uid/gids can do certain types of IP communication.)
[0] That is to say, remove the restriction that one must run as root to bind to ports < 1024.
[1] https://www.debian-administration.org/article/120/Applicatio... [2]
[2] Even though the kconfig option has changed names, it appears to serve the same function (see the Owner section of [3])
It's a good thing raw sockets require root. Raw sockets are incredibly powerful tools that can be used for all sorts of mischief (including source address spoofing in case of udp, so perfect for various dos attacks)
It's a feature if some clueless user that just downloaded some Trojan flash player update can't fire off a DNS reflection attack against a third party
They arise quite frequently if you're running non-standard network services.
I have a service that I don't want to run as a root user, even temporarily, and therefore it needs to bind to a non-privileged port. In principle, another service could bind to the same port if it goes down.
> However, do you agree that removing the notion of privileged ports...
I'm not convinced people are suggesting only removing the privileged port restriction, but rather replacing it with something more flexible.
Just being able to lock ports down to a uid would suffice for many use cases and could work the same way as the legacy system by default, with ports <1024 reserved for root and other ports not reserved. Then, e.g.
# echo "8080 <MYUID>" > /proc/sys/net/ipv4/conf/all/portsec/register
and no-one but me can bind to 8080 on any interface.
Of course there are more extensive proposed solutions, but this would solve every problem I've ever had with binding to a privileged (or not) port.
> There is also this which lets you do something like what Windows Firewall does and use iptables to restrict which uid/gids can do certain types of IP communication
That's only a solution if I can bind to the port in the first place, and in a way that doesn't open me up to having my port hijacked by some other process, like on Windows.
It can be done in userspace with `authbind` (based on some LD_PRELOAD magic).
# apt-get install authbind
# echo '0.0.0.0,8080-8081' >> /etc/authbind/byuid/$(id -u $TARGETUSER)
$ authbind my-daemon