r-vdpandRasheeq Azad
1ac3c5dc99
Writing a multi-line /proc/<pid>/[ug]id_map only requires
CAP_SETUID/CAP_SETGID over the parent user namespace, not full root.
shadow's own --with-fcaps install mode (70971457b761) sets exactly
cap_setuid+ep / cap_setgid+ep, and Arch, Fedora and Debian have shipped
these binaries with file capabilities instead of setuid for years.
The setuid variant already drops to the same single capability before
the uid_map write (see lib/idmapping.c), so the privilege at the point
attacker-controlled data reaches the kernel is unchanged. The reduction
is in the startup window: with file capabilities the process never has
euid 0 and never holds the full capability set during NSS lookups,
/etc/subuid parsing and /proc/<pid> opening.
The only functional difference is that mapping host uid 0 into a child
namespace additionally needs CAP_SETFCAP, which the setuid path got
implicitly. NixOS never puts uid 0 into auto-allocated subuid ranges,
and granting it manually is a deliberate root-equivalent configuration;
the release notes document the override for that case.
nixosTests.{shadow,podman,docker-rootless} pass; the latter two
exercise newuidmap/newgidmap via rootless containers.
Supersedes #461172.
Co-authored-by: Rasheeq Azad <rasheeqhere@gmail.com>
Nixpkgs is a collection of over 120,000 software packages that can be installed with the Nix package manager. It also implements NixOS, a purely-functional Linux distribution.
Manuals
- NixOS Manual - how to install, configure, and maintain a purely-functional Linux distribution
- Nixpkgs Manual - contributing to Nixpkgs and using programming-language-specific Nix expressions
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Artifacts successfully built with Hydra are published to cache at https://cache.nixos.org/. When successful build and test criteria are met, the Nixpkgs expressions are distributed via Nix channels.
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