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setup-root: Fix overlay permissions #294

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Merged
cgwalters merged 1 commit into from
May 15, 2026
+9 −4
Merged

setup-root: Fix overlay permissions #294

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13 changes: 9 additions & 4 deletions crates/composefs-setup-root/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -111,8 +111,8 @@ fn open_dir(dirfd: impl AsFd, name: impl AsRef<Path> + Debug) -> rustix::io::Res
})
}

fn ensure_dir(dirfd: impl AsFd, name: &str) -> rustix::io::Result<OwnedFd> {
match mkdirat(dirfd.as_fd(), name, 0o700.into()) {
fn ensure_dir(dirfd: impl AsFd, name: &str, mode: Mode) -> rustix::io::Result<OwnedFd> {
match mkdirat(dirfd.as_fd(), name, mode) {
Ok(()) | Err(Errno::EXIST) => {}
Err(err) => Err(err)?,
}
Expand Down Expand Up @@ -143,8 +143,13 @@ fn mount_tmpfs() -> Result<OwnedFd> {
}

fn overlay_state(base: impl AsFd, state: impl AsFd, source: &str) -> Result<()> {
let upper = ensure_dir(state.as_fd(), "upper")?;
let work = ensure_dir(state.as_fd(), "work")?;
// upper must be 0755: the overlayfs merged view inherits permissions from
// upperdir, so 0700 would make / (or the mounted subdir) inaccessible to
// non-root processes (dbus, anything that drops privileges).
// work is kernel-internal and never visible in the merged view; 0700 is fine.
// See: https://github.com/composefs/composefs-rs/issues/287
let upper = ensure_dir(state.as_fd(), "upper", 0o755.into())?;
let work = ensure_dir(state.as_fd(), "work", 0o700.into())?;

let overlayfs = FsHandle::open("overlay")?;
fsconfig_set_string(overlayfs.as_fd(), "source", source)?;
Expand Down