Re:Giving up on Julia (2016)
by ghusbands on Sunday August 18, 2019 @11:51PM
(#20734750)
A long-running background interpreter carries significant security risks, though. A process that lacks most linux capabilities could use it to regain access to things it shouldn't have access to. A process could interpose itself and get access to data and code it shouldn't. If there are multiple users involved, one could bypass ACLs and similar. Essentially, you're removing a significant proportion of the security guarantees the OS provides around isolated processes.
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Some of the concerns you raise can be addressed. For example, make the daemon and socket per-user and give the socket 600 permissions. Also, the SCM_CREDENTIALS message (on Linux) or LOCAL_PEERCRED/getpeereid (macOS/*BSD) can be used to validate the caller has expected UID.
The issue with missing-normal-capability processes is more difficult to address. One possibility, at least on Linux, would be to get the pid from SCM_CREDENTIALS message, and then read /proc/$PID/status to check capability bits. It could default to denying access to processes with less capabilities than it itself has.
(SCM_SECURITY can be used to pass the SELinux security label from client to server, which could also be used as a security measure; maybe the server could refuse access to processes running with a different label, or have a whitelist of allowed labels; if SELinux is being used to sandbox a process, that would prevent it from accessing the background interpreter unless that was explicitly allowed by whitelisting.)