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libstore: Make our sandbox pivot_root directory accessible to ourself

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If you have the Nix store mounted from a nonlocal filesystem whose
exporter is not running as root, making the directory mode 000 makes it
inaccessible to that remote unprivileged user and therefore breaks the
build. (Specifically, I am running into this with a virtiofs mount using
Apple Virtualization.framework as a non-root user, but I expect the
same thing would happen with virtiofs in qemu on Linux as a non-root
user or with various userspace network file servers.)

Make the directory mode 500 (dr-x------) to make the sandbox work in
this use case, which explicitly conveys our intention to read and search
the directory.  The code only works because root can already bypass
directory checks, so this does not actually grant more permissions to
the directory owner / does not make the sandbox less secure.

(cherry picked from commit 5a794d9366)
This commit is contained in:
Geoffrey Thomas 2024-10-12 19:55:58 -04:00 • committed by Mergify
parent e0c8b0fc4f
commit 24542a7b96
1 changed files with 1 additions and 1 deletions
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2
src/libstore/unix/build/local-derivation-goal.cc
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@ -1966,7 +1966,7 @@ void LocalDerivationGoal::runChild()
if (chdir(chrootRootDir.c_str()) == -1)
throw SysError("cannot change directory to '%1%'", chrootRootDir);
if (mkdir("real-root", 0) == -1)
if (mkdir("real-root", 0500) == -1)
throw SysError("cannot create real-root directory");
if (pivot_root(".", "real-root") == -1)