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Merge pull request #3897 from lucab/ups/intercept-useradd
core: wrap and intercept `useradd` calls in scriptlets
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//! CLI handler for intercepted `useradd`. | ||
// SPDX-License-Identifier: Apache-2.0 OR MIT | ||
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use anyhow::{anyhow, Context, Result}; | ||
use cap_std::fs::{Dir, Permissions}; | ||
use cap_std_ext::prelude::CapStdExtDirExt; | ||
use clap::{Arg, Command}; | ||
use std::io::Write; | ||
use std::os::unix::prelude::PermissionsExt; | ||
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/// Entrypoint for (the rpm-ostree implementation of) `useradd`. | ||
pub(crate) fn entrypoint(args: &[&str]) -> Result<()> { | ||
fail::fail_point!("intercept_useradd_ok", |_| Ok(())); | ||
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// Extract the package name from rpm-ostree/bwrap environment. | ||
// This also works as a sanity check to ensure we are running in | ||
// the context of a scriptlet. | ||
static SCRIPT_PKG_VAR: &str = "RPMOSTREE_SCRIPT_PKG_NAME"; | ||
let pkgname = std::env::var(SCRIPT_PKG_VAR) | ||
.with_context(|| format!("Failed to access {SCRIPT_PKG_VAR} environment variable"))?; | ||
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// This parses the same CLI surface as the real `useradd`, | ||
// but in the end we only extract the username and UID/GID | ||
// (if present). | ||
let matches = cli_cmd().get_matches_from(args); | ||
let username = matches | ||
.value_of("username") | ||
.ok_or_else(|| anyhow!("missing required username argument"))?; | ||
let uid = matches | ||
.value_of("uid") | ||
.map(|s| s.parse::<u32>()) | ||
.transpose()?; | ||
let group = matches.value_of("group"); | ||
let gecos = matches.value_of("comment"); | ||
let homedir = matches.value_of("homedir"); | ||
let shell = matches.value_of("shell"); | ||
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if !matches.is_present("system") { | ||
eprintln!("Trying to create non-system user '{username}'; this will become an error in the future."); | ||
} | ||
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let rootdir = Dir::open_ambient_dir("/", cap_std::ambient_authority())?; | ||
generate_sysusers_fragment( | ||
&rootdir, | ||
&pkgname, | ||
username, | ||
(uid, group), | ||
gecos, | ||
homedir, | ||
shell, | ||
)?; | ||
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Ok(()) | ||
} | ||
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/// CLI parser, matches <https://linux.die.net/man/8/useradd>. | ||
fn cli_cmd() -> Command<'static> { | ||
let name = "useradd"; | ||
Command::new(name) | ||
.bin_name(name) | ||
.about("create a new user") | ||
.arg( | ||
Arg::new("comment") | ||
.short('c') | ||
.long("comment") | ||
.takes_value(true), | ||
) | ||
.arg( | ||
Arg::new("homedir") | ||
.short('d') | ||
.long("home-dir") | ||
.takes_value(true), | ||
) | ||
.arg(Arg::new("group").short('g').long("gid").takes_value(true)) | ||
.arg(Arg::new("system").short('r').long("system")) | ||
.arg(Arg::new("shell").short('s').long("shell").takes_value(true)) | ||
.arg(Arg::new("uid").short('u').long("uid").takes_value(true)) | ||
.arg(Arg::new("username").required(true)) | ||
} | ||
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/// Write a sysusers.d configuration fragment for the given user. | ||
/// | ||
/// This returns whether a new fragment has been actually written | ||
/// to disk. | ||
fn generate_sysusers_fragment( | ||
rootdir: &Dir, | ||
pkgname: &str, | ||
username: &str, | ||
id: (Option<u32>, Option<&str>), | ||
gecos: Option<&str>, | ||
homedir: Option<&str>, | ||
shell: Option<&str>, | ||
) -> Result<bool> { | ||
static SYSUSERS_DIR: &str = "usr/lib/sysusers.d"; | ||
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// The filename of the configuration fragment is in fact a public | ||
// API, because users may have masked it in /etc. Do not change this. | ||
let filename = format!("40-pkg-{pkgname}-user-{username}.conf"); | ||
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rootdir.create_dir_all(SYSUSERS_DIR)?; | ||
let conf_dir = rootdir.open_dir(SYSUSERS_DIR)?; | ||
if conf_dir.exists(&filename) { | ||
return Ok(false); | ||
} | ||
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let id = match id { | ||
(Some(uid), Some(group)) => format!("{uid}:{group}"), | ||
(Some(id), None) => format!("{id}"), | ||
(None, Some(group)) => format!("-:{group}"), | ||
(None, None) => "-".to_string(), | ||
}; | ||
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let gecos = gecos | ||
.map(|g| format!("\"{g}\"")) | ||
.unwrap_or_else(|| "-".to_string()); | ||
let homedir = homedir | ||
.map(|h| { | ||
match h { | ||
// Detect and match systemd default: | ||
// https://github.com/systemd/systemd/blob/v251/src/sysusers/sysusers.c#L471-L472 | ||
"" | "/" => "-", | ||
x => x, | ||
} | ||
.to_string() | ||
}) | ||
.unwrap_or_else(|| "-".to_string()); | ||
let shell = shell | ||
.map(|s| { | ||
match s { | ||
// Detect and match systemd default: | ||
// https://github.com/systemd/systemd/blob/v251/meson.build#L633 | ||
"" | "/sbin/nologin" | "/usr/sbin/nologin" => "-", | ||
x => x, | ||
} | ||
.to_string() | ||
}) | ||
.unwrap_or_else(|| "-".to_string()); | ||
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conf_dir.atomic_replace_with(&filename, |fragment| -> Result<()> { | ||
let perms = Permissions::from_mode(0o644); | ||
fragment.get_mut().as_file_mut().set_permissions(perms)?; | ||
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fragment.write_all(b"# Generated by rpm-ostree\n")?; | ||
let entry = format!("u {username} {id} {gecos} {homedir} {shell}\n"); | ||
fragment.write_all(entry.as_bytes())?; | ||
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Ok(()) | ||
})?; | ||
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Ok(true) | ||
} | ||
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#[cfg(test)] | ||
mod test { | ||
use super::*; | ||
use std::io::Read; | ||
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#[test] | ||
fn test_clap_cmd() { | ||
cli_cmd().debug_assert(); | ||
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let cmd = cli_cmd(); | ||
let static_uid = [ | ||
"/usr/sbin/useradd", | ||
"-d", | ||
"testhome", | ||
"-u", | ||
"7", | ||
"-g", | ||
"root", | ||
"halt", | ||
]; | ||
let matches = cmd.try_get_matches_from(static_uid).unwrap(); | ||
assert_eq!(matches.value_of("homedir"), Some("testhome")); | ||
assert_eq!(matches.value_of("uid"), Some("7")); | ||
assert_eq!(matches.value_of("group"), Some("root")); | ||
assert_eq!(matches.value_of("username"), Some("halt")); | ||
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let cmd = cli_cmd(); | ||
let dynamic_uid = ["/usr/sbin/useradd", "-r", "-s", "testshell", "clevis"]; | ||
let matches = cmd.try_get_matches_from(dynamic_uid).unwrap(); | ||
assert!(matches.contains_id("system")); | ||
assert_eq!(matches.value_of("uid"), None); | ||
assert_eq!(matches.value_of("username"), Some("clevis")); | ||
assert_eq!(matches.value_of("shell"), Some("testshell")); | ||
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let err_cases = [vec!["/usr/sbin/useradd"]]; | ||
for input in err_cases { | ||
let cmd = cli_cmd(); | ||
cmd.try_get_matches_from(input).unwrap_err(); | ||
} | ||
} | ||
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#[test] | ||
fn test_fragment_generation() { | ||
let tmpdir = cap_tempfile::tempdir(cap_tempfile::ambient_authority()).unwrap(); | ||
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let groups = [ | ||
("first_user", (Some(42), None), true, "42"), | ||
("first_user", (None, None), false, "42"), | ||
("second_user", (None, None), true, "-"), | ||
( | ||
"third_user", | ||
(None, Some("some_group")), | ||
true, | ||
"-:some_group", | ||
), | ||
]; | ||
for entry in groups { | ||
let generated = generate_sysusers_fragment( | ||
&tmpdir, | ||
"foopkg", | ||
entry.0, | ||
entry.1, | ||
Some("freeform description"), | ||
None, | ||
None, | ||
) | ||
.unwrap(); | ||
assert_eq!(generated, entry.2, "{:?}", entry); | ||
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let path = format!("usr/lib/sysusers.d/40-pkg-foopkg-user-{}.conf", entry.0); | ||
assert!(tmpdir.is_file(&path)); | ||
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let mut fragment = tmpdir.open(&path).unwrap(); | ||
let mut content = String::new(); | ||
fragment.read_to_string(&mut content).unwrap(); | ||
let expected = format!( | ||
"# Generated by rpm-ostree\nu {} {} \"freeform description\" - -\n", | ||
entry.0, entry.3 | ||
); | ||
assert_eq!(content, expected) | ||
} | ||
} | ||
} |
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,13 @@ | ||
#!/usr/bin/bash | ||
# Used by rpmostree-core.c to intercept `useradd` calls. | ||
# We want to learn about user creation and distinguish between | ||
# static and dynamic IDs, in order to auto-generate relevant | ||
# `sysusers.d` fragments. | ||
# See also https://github.com/coreos/rpm-ostree/issues/3762 | ||
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if test -v RPMOSTREE_EXP_BRIDGE_SYSUSERS; then | ||
rpm-ostree scriptlet-intercept useradd -- "$0" "$@" | ||
fi | ||
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# Forward to the real `useradd` for group creation. | ||
exec /usr/sbin/useradd.rpmostreesave "$@" |