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0a9cecc35a
Our more thorough parametrised tests uncovered that with the changes for supporting DynamicUser, we now have the situation that for static users the root directory within the confined environment is now writable for the user in question. This is obviously not what we want and I'd consider that a regression. However while discussing this with @ju1m and my suggestion being to set TemporaryFileSystem to "/" (as we had previously), they had an even better idea[1]: > The goal is to deny write access to / to non-root users, > > * TemporaryFileSystem=/ gives us that through the ownership of / by > root (instead of the service's user inherited from > RuntimeDirectory=). > * ProtectSystem=strict gives us that by mounting / read-only (while > keeping its ownership to the service's user). > > To avoid the incompatibilities of TemporaryFileSystem=/ mentioned > above, I suggest to mount / read-only in all cases with > ReadOnlyPaths = [ "+/" ]: > > ... > > I guess this would require at least two changes to the current tests: > > 1. to no longer expect root to be able to write to some paths (like > /bin) (at least not without first remounting / in read-write > mode). > 2. to no longer expect non-root users to fail to write to certain > paths with a "permission denied" error code, but with a > "read-only file system" error code. I like the solution with ReadOnlyPaths even more because it further reduces the attack surface if the user is root. In chroot-only mode this is especially useful, since if there are no other bind-mounted paths involved in the unit configuration, the whole file system within the confined environment is read-only. [1]: https://github.com/NixOS/nixpkgs/pull/289593#discussion_r1586794215 Signed-off-by: aszlig <aszlig@nix.build> |
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