Allow root uid/gid (0) in sandbox userns when allowNewPrivileges #2525
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If Nix is run with the --allow-new-privileges option then it should be possible to run setuid binaries to gain root access. However, this did not work in practice because the root user/group did not exist in the sandbox due to exclusion from the kernel user-namespace. The uid would always be nixbld (1000) even when executing a setuid-root binary. This change adds uid/gid 0 to the sandbox userns only when --allow-new-privileges is enabled and makes setuid work as expected. Note: This makes it effective to *run* setuid executables but it does not make it possible to create them. This means that in practice to gain root in the sandbox you must both provide --allow-new-privileges and also add a suitable binary to the Nix sandbox path. Resolves NixOS#2522.
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Maybe there should also be an entry added to |
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I marked this as stale due to inactivity. → More info |
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I closed this issue due to inactivity. → More info |
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If Nix is run with the
--allow-new-privilegesoption then it should be possible to run setuid binaries to gain root access. However, this did not work in practice because the root user/group did not exist in the sandbox due to exclusion from the kernel user-namespace. The uid would always be nixbld (1000) even when executing a setuid-root binary.This change adds uid/gid 0 to the sandbox userns only when
--allow-new-privilegesis enabled and makes setuid work as expected.Note: This makes it effective to run setuid executables but it does not make it possible to create them. This means that in practice to gain root in the sandbox you must both provide
--allow-new-privilegesand also add a suitable binary to the Nix sandbox path.Resolves #2522.