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switch-to-configuration-ng: derive user GID/runtime from filesystem

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Avoid TOCTOU race against logind async GC: replace D-Bus Properties::get
for GID/RuntimePath with stat(/run/user/<uid>), which is atomic.

Relates: #429884
Assisted-by: opencode (sst) with glm-5.2
This commit is contained in:
LuoChen
2026-08-08 09:21:54 +08:00
parent 8e6019ecac
commit 5c636d9297
1 changed files with 30 additions and 15 deletions
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45
pkgs/by-name/sw/switch-to-configuration-ng/src/main.rs
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@@ -6,7 +6,8 @@ use std::{
cell::RefCell,
collections::HashMap,
io::{BufRead, Read, Write},
os::unix::{fs::PermissionsExt, process::CommandExt},
os::unix::fs::{MetadataExt, PermissionsExt},
os::unix::process::CommandExt,
path::{Path, PathBuf},
rc::Rc,
str::FromStr,
@@ -2384,19 +2385,33 @@ won't take effect until you reboot the system.
exit_code = 4;
}
Ok(users) => {
for (uid, name, user_dbus_path) in users {
let proxy = dbus_conn.with_proxy(
"org.freedesktop.login1",
&user_dbus_path,
Duration::from_millis(5000),
);
let gid: u32 = proxy
.get("org.freedesktop.login1.User", "GID")
.with_context(|| format!("Failed to get GID for {name}"))?;
let runtime_path: String = proxy
.get("org.freedesktop.login1.User", "RuntimePath")
.with_context(|| format!("Failed to get runtime directory for {name}"))?;
for (uid, name, _user_dbus_path) in users {
// Derive GID and runtime path from the filesystem instead of querying
// logind via D-Bus, which races against logind's async GC of user
// objects (list_users snapshot → Properties::get hits UnknownObject).
// /run/user/<uid> exists iff the user manager is active (BindsTo= on
// user@.service), so stat() is an atomic, race-free liveness check.
let runtime_path = PathBuf::from(format!("/run/user/{uid}"));
let metadata = match std::fs::metadata(&runtime_path) {
Ok(m) => m,
Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
eprintln!(
"skipping user {name}: {} not found \
(user manager not running)",
runtime_path.display()
);
continue;
}
Err(err) => {
eprintln!(
"warning: failed to stat {} for user {name}; \
skipping: {err}",
runtime_path.display()
);
exit_code = 4;
continue;
}
};
eprintln!("reloading user units for {name}...");
let myself = Path::new("/proc/self/exe")
@@ -2406,7 +2421,7 @@ won't take effect until you reboot the system.
log::debug!("Performing user switch for {name}");
let status = std::process::Command::new(&myself)
.uid(uid)
.gid(gid)
.gid(metadata.gid())
.env_clear()
.env("XDG_RUNTIME_DIR", runtime_path)
.env("__NIXOS_SWITCH_TO_CONFIGURATION_PARENT_EXE", &myself)