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Replace socket authentication mechanism with SO_PEERCRED

This commit is contained in:
Oystein Kristoffer Tveit 2024-08-18 22:20:56 +02:00
parent 94c9a54c14
commit 53f19b3d05
Signed by: oysteikt
GPG Key ID: 9F2F7D8250F35146
5 changed files with 14 additions and 479 deletions
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2
Cargo.toml
View File

@ -16,7 +16,7 @@ futures-util = "0.3.30"
indoc = "2.0.5"
itertools = "0.13.0"
log = "0.4.22"
nix = { version = "0.29.0", features = ["fs", "process", "user"] }
nix = { version = "0.29.0", features = ["fs", "process", "socket", "user"] }
prettytable = "0.10.0"
rand = "0.8.5"
ratatui = { version = "0.28.0", optional = true }

35
src/core/bootstrap.rs
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@ -6,15 +6,10 @@ use std::os::unix::net::UnixStream as StdUnixStream;
use tokio::net::UnixStream as TokioUnixStream;
use crate::{
core::{
bootstrap::authenticated_unix_socket::client_authenticate,
common::{UnixUser, DEFAULT_CONFIG_PATH, DEFAULT_SOCKET_PATH},
},
core::common::{UnixUser, DEFAULT_CONFIG_PATH, DEFAULT_SOCKET_PATH},
server::{config::read_config_form_path, server_loop::handle_requests_for_single_session},
};
pub mod authenticated_unix_socket;
// TODO: this function is security critical, it should be integration tested
// in isolation.
/// Drop privileges to the real user and group of the process.
@ -57,25 +52,11 @@ pub fn bootstrap_server_connection_and_drop_privileges(
log::debug!("Starting the server connection bootstrap process");
let (socket, do_authenticate) = bootstrap_server_connection(server_socket_path, config_path)?;
let socket = bootstrap_server_connection(server_socket_path, config_path)?;
drop_privs()?;
let result: anyhow::Result<StdUnixStream> = if do_authenticate {
tokio::runtime::Builder::new_current_thread()
.enable_all()
.build()
.unwrap()
.block_on(async {
let mut socket = TokioUnixStream::from_std(socket)?;
client_authenticate(&mut socket, None).await?;
Ok(socket.into_std()?)
})
} else {
Ok(socket)
};
result
Ok(socket)
}
/// Inner function for [`bootstrap_server_connection_and_drop_privileges`].
@ -83,12 +64,12 @@ pub fn bootstrap_server_connection_and_drop_privileges(
fn bootstrap_server_connection(
socket_path: Option<PathBuf>,
config_path: Option<PathBuf>,
) -> anyhow::Result<(StdUnixStream, bool)> {
) -> anyhow::Result<StdUnixStream> {
// TODO: ensure this is both readable and writable
if let Some(socket_path) = socket_path {
log::debug!("Connecting to socket at {:?}", socket_path);
return match StdUnixStream::connect(socket_path) {
Ok(socket) => Ok((socket, true)),
Ok(socket) => Ok(socket),
Err(e) => match e.kind() {
std::io::ErrorKind::NotFound => Err(anyhow::anyhow!("Socket not found")),
std::io::ErrorKind::PermissionDenied => Err(anyhow::anyhow!("Permission denied")),
@ -103,12 +84,12 @@ fn bootstrap_server_connection(
}
log::debug!("Starting server with config at {:?}", config_path);
return invoke_server_with_config(config_path).map(|socket| (socket, false));
return invoke_server_with_config(config_path);
}
if fs::metadata(DEFAULT_SOCKET_PATH).is_ok() {
return match StdUnixStream::connect(DEFAULT_SOCKET_PATH) {
Ok(socket) => Ok((socket, true)),
Ok(socket) => Ok(socket),
Err(e) => match e.kind() {
std::io::ErrorKind::NotFound => Err(anyhow::anyhow!("Socket not found")),
std::io::ErrorKind::PermissionDenied => Err(anyhow::anyhow!("Permission denied")),
@ -119,7 +100,7 @@ fn bootstrap_server_connection(
let config_path = PathBuf::from(DEFAULT_CONFIG_PATH);
if fs::metadata(&config_path).is_ok() {
return invoke_server_with_config(config_path).map(|socket| (socket, false));
return invoke_server_with_config(config_path);
}
anyhow::bail!("No socket path or config path provided, and no default socket or config found");

439
src/core/bootstrap/authenticated_unix_socket.rs
View File

@ -1,439 +0,0 @@
//! This module provides a way to authenticate a client uid to a server over a Unix socket.
//! This is needed so that the server can trust the client's uid, which it depends on to
//! make modifications for that user in the database. It is crucial that the server can trust
//! that the client is the unix user it claims to be.
//!
//! This works by having the client respond to a challenge on a socket that is verifiably owned
//! by the client. In more detailed steps, the following should happen:
//!
//! 1. Before initializing it's request, the client should open an "authentication" socket with permissions 644
//! and owned by the uid of the current user.
//! 2. The client opens a request to the server on the "normal" socket where the server is listening,
//! In this request, the client should include the following:
//! - The address of it's authentication socket
//! - The uid of the user currently using the client
//! - A challenge string that has been randomly generated
//! 3. The server validates the following:
//! - The address of the auth socket is valid
//! - The owner of the auth socket address is the same as the uid
//! 4. Server connects to the auth socket address and receives another challenge string.
//! The server should close the connection after receiving the challenge string.
//! 5. Server verifies that the challenge is the same as the one it originally received.
//! It responds to the client with an "Authenticated" message if the challenge matches,
//! or an error message if it does not.
//! 6. Client closes the authentication socket. Normal socket is used for communication.
//!
//! Note that the server can at any point in the process send an error message to the client
//! over it's initial connection, and the client should respond by closing the authentication
//! socket, it's connection to the normal socket, and reporting the error to the user.
//!
//! Also note that it is essential that the client does not send any sensitive information
//! over it's authentication socket, since it is readable by any user on the system.
// TODO: rewrite this so that it can be used with a normal std::os::unix::net::UnixStream
use std::os::unix::io::AsRawFd;
use std::path::{Path, PathBuf};
use async_bincode::{tokio::AsyncBincodeStream, AsyncDestination};
use derive_more::derive::{Display, Error};
use futures::{SinkExt, StreamExt};
use nix::{sys::stat, unistd::Uid};
use rand::distributions::Alphanumeric;
use rand::Rng;
use serde::{Deserialize, Serialize};
use tokio::net::{UnixListener, UnixStream};
use tokio_util::sync::CancellationToken;
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub enum ClientRequest {
Initialize {
uid: u32,
challenge: u64,
auth_socket: String,
},
Cancel,
}
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Display, Error)]
pub enum ServerResponse {
Authenticated,
ChallengeDidNotMatch,
ServerError(ServerError),
}
// TODO: wrap more data into the errors
#[derive(Debug, Display, PartialEq, Serialize, Deserialize, Clone, Error)]
pub enum ServerError {
InvalidRequest,
UnableToReadPermissionsFromAuthSocket,
CouldNotConnectToAuthSocket,
AuthSocketClosedEarly,
UidMismatch,
ChallengeMismatch,
InvalidChallenge,
}
#[derive(Debug, PartialEq, Display, Error)]
pub enum ClientError {
UnableToConnectToServer,
UnableToOpenAuthSocket,
UnableToConfigureAuthSocket,
AuthSocketClosedEarly,
UnableToCloseAuthSocket,
AuthenticationError,
UnableToParseServerResponse,
NoServerResponse,
ServerError(ServerError),
}
async fn create_auth_socket(socket_addr: &PathBuf) -> Result<UnixListener, ClientError> {
let auth_socket =
UnixListener::bind(socket_addr).map_err(|_err| ClientError::UnableToOpenAuthSocket)?;
stat::fchmod(
auth_socket.as_raw_fd(),
stat::Mode::S_IRUSR | stat::Mode::S_IWUSR | stat::Mode::S_IRGRP,
)
.map_err(|_err| ClientError::UnableToConfigureAuthSocket)?;
Ok(auth_socket)
}
type ClientToServerStream<'a> =
AsyncBincodeStream<&'a mut UnixStream, ServerResponse, ClientRequest, AsyncDestination>;
type ServerToClientStream<'a> =
AsyncBincodeStream<&'a mut UnixStream, ClientRequest, ServerResponse, AsyncDestination>;
// TODO: make the challenge constant size and use socket directly, this is overkill
type AuthStream<'a> = AsyncBincodeStream<&'a mut UnixStream, u64, u64, AsyncDestination>;
// TODO: add timeout
// TODO: respect $XDG_RUNTIME_DIR and $TMPDIR
const AUTH_SOCKET_NAME: &str = "mysqladm-rs-cli-auth.sock";
pub async fn client_authenticate(
normal_socket: &mut UnixStream,
auth_socket_dir: Option<PathBuf>,
) -> Result<(), ClientError> {
let random_prefix: String = rand::thread_rng()
.sample_iter(&Alphanumeric)
.take(16)
.map(char::from)
.collect();
let socket_name = format!("{}-{}", random_prefix, AUTH_SOCKET_NAME);
let auth_socket_address = auth_socket_dir
.unwrap_or(std::env::temp_dir())
.join(socket_name);
client_authenticate_with_auth_socket_address(normal_socket, &auth_socket_address).await
}
async fn client_authenticate_with_auth_socket_address(
normal_socket: &mut UnixStream,
auth_socket_address: &PathBuf,
) -> Result<(), ClientError> {
let auth_socket = create_auth_socket(auth_socket_address).await?;
let result =
client_authenticate_with_auth_socket(normal_socket, auth_socket, auth_socket_address).await;
std::fs::remove_file(auth_socket_address)
.map_err(|_err| ClientError::UnableToCloseAuthSocket)?;
result
}
async fn client_authenticate_with_auth_socket(
normal_socket: &mut UnixStream,
auth_socket: UnixListener,
auth_socket_address: &Path,
) -> Result<(), ClientError> {
let challenge = rand::random::<u64>();
let uid = nix::unistd::getuid();
let mut normal_socket: ClientToServerStream =
AsyncBincodeStream::from(normal_socket).for_async();
let challenge_replier_cancellation_token = CancellationToken::new();
let challenge_replier_cancellation_token_clone = challenge_replier_cancellation_token.clone();
let challenge_replier_handle = tokio::spawn(async move {
loop {
tokio::select! {
socket = auth_socket.accept() =>
{
match socket {
Ok((mut conn, _addr)) => {
let mut stream: AuthStream = AsyncBincodeStream::from(&mut conn).for_async();
stream.send(challenge).await.ok();
stream.close().await.ok();
}
Err(_err) => return Err(ClientError::AuthSocketClosedEarly),
}
}
_ = challenge_replier_cancellation_token_clone.cancelled() => {
break Ok(());
}
}
}
});
let client_hello = ClientRequest::Initialize {
uid: uid.into(),
challenge,
auth_socket: auth_socket_address
.to_str()
.ok_or(ClientError::UnableToConfigureAuthSocket)?
.to_owned(),
};
normal_socket
.send(client_hello)
.await
.map_err(|err| match *err {
bincode::ErrorKind::Io(_err) => ClientError::UnableToConnectToServer,
_ => ClientError::NoServerResponse,
})?;
match normal_socket.next().await {
Some(Ok(ServerResponse::Authenticated)) => {}
Some(Ok(ServerResponse::ChallengeDidNotMatch)) => {
return Err(ClientError::AuthenticationError)
}
Some(Ok(ServerResponse::ServerError(err))) => return Err(ClientError::ServerError(err)),
Some(Err(err)) => match *err {
bincode::ErrorKind::Io(_err) => return Err(ClientError::NoServerResponse),
_ => return Err(ClientError::UnableToParseServerResponse),
},
None => return Err(ClientError::NoServerResponse),
}
challenge_replier_cancellation_token.cancel();
challenge_replier_handle.await.ok();
Ok(())
}
macro_rules! report_server_error_and_return {
($normal_socket:expr, $err:expr) => {{
$normal_socket
.send(ServerResponse::ServerError($err))
.await
.ok();
return Err($err);
}};
}
pub async fn server_authenticate(normal_socket: &mut UnixStream) -> Result<Uid, ServerError> {
_server_authenticate(normal_socket, None).await
}
pub async fn _server_authenticate(
normal_socket: &mut UnixStream,
unix_user_uid: Option<u32>,
) -> Result<Uid, ServerError> {
let mut normal_socket: ServerToClientStream =
AsyncBincodeStream::from(normal_socket).for_async();
let (uid, challenge, auth_socket) = match normal_socket.next().await {
Some(Ok(ClientRequest::Initialize {
uid,
challenge,
auth_socket,
})) => (uid, challenge, auth_socket),
// TODO: more granular errros
_ => report_server_error_and_return!(normal_socket, ServerError::InvalidRequest),
};
let auth_socket_uid = match unix_user_uid {
Some(uid) => uid,
None => match stat::stat(auth_socket.as_str()) {
Ok(stat) => stat.st_uid,
Err(_err) => report_server_error_and_return!(
normal_socket,
ServerError::UnableToReadPermissionsFromAuthSocket
),
},
};
if uid != auth_socket_uid {
report_server_error_and_return!(normal_socket, ServerError::UidMismatch);
}
let mut authenticated_unix_socket = match UnixStream::connect(auth_socket).await {
Ok(socket) => socket,
Err(_err) => {
report_server_error_and_return!(normal_socket, ServerError::CouldNotConnectToAuthSocket)
}
};
let mut authenticated_unix_socket: AuthStream =
AsyncBincodeStream::from(&mut authenticated_unix_socket).for_async();
let challenge_2 = match authenticated_unix_socket.next().await {
Some(Ok(challenge)) => challenge,
Some(Err(_)) => {
report_server_error_and_return!(normal_socket, ServerError::InvalidChallenge)
}
None => report_server_error_and_return!(normal_socket, ServerError::AuthSocketClosedEarly),
};
authenticated_unix_socket.close().await.ok();
if challenge != challenge_2 {
normal_socket
.send(ServerResponse::ChallengeDidNotMatch)
.await
.ok();
return Err(ServerError::ChallengeMismatch);
}
normal_socket.send(ServerResponse::Authenticated).await.ok();
Ok(Uid::from_raw(uid))
}
#[cfg(test)]
mod test {
use super::*;
use std::time::Duration;
use tokio::time::sleep;
#[tokio::test]
async fn test_valid_authentication() {
let (mut client, mut server) = UnixStream::pair().unwrap();
let client_handle =
tokio::spawn(async move { client_authenticate(&mut client, None).await });
let server_handle = tokio::spawn(async move { server_authenticate(&mut server).await });
client_handle.await.unwrap().unwrap();
server_handle.await.unwrap().unwrap();
}
#[tokio::test]
async fn test_ensure_auth_socket_does_not_exist() {
let (mut client, mut server) = UnixStream::pair().unwrap();
let client_handle = tokio::spawn(async move {
client_authenticate_with_auth_socket_address(
&mut client,
&PathBuf::from("/tmp/test_auth_socket_does_not_exist.sock"),
)
.await
});
let server_handle = tokio::spawn(async move { server_authenticate(&mut server).await });
client_handle.await.unwrap().unwrap();
server_handle.await.unwrap().unwrap();
}
#[tokio::test]
async fn test_uid_mismatch() {
let (mut client, mut server) = UnixStream::pair().unwrap();
let client_handle = tokio::spawn(async move {
let err = client_authenticate(&mut client, None).await;
assert_eq!(err, Err(ClientError::ServerError(ServerError::UidMismatch)));
});
let server_handle = tokio::spawn(async move {
let uid: u32 = nix::unistd::getuid().into();
let err = _server_authenticate(&mut server, Some(uid + 1)).await;
assert_eq!(err, Err(ServerError::UidMismatch));
});
client_handle.await.unwrap();
server_handle.await.unwrap();
}
#[tokio::test]
async fn test_snooping_connection() {
let (mut client, mut server) = UnixStream::pair().unwrap();
let socket_path = std::env::temp_dir().join("socket_to_snoop.sock");
let socket_path_clone = socket_path.clone();
let client_handle = tokio::spawn(async move {
client_authenticate_with_auth_socket_address(&mut client, &socket_path_clone).await
});
for i in 0..100 {
if socket_path.exists() {
break;
}
sleep(Duration::from_millis(10)).await;
if i == 99 {
panic!("Socket not created after 1 second, assuming test failure");
}
}
let mut snooper = UnixStream::connect(socket_path.clone()).await.unwrap();
let mut snooper: AuthStream = AsyncBincodeStream::from(&mut snooper).for_async();
let message = snooper.next().await.unwrap().unwrap();
let mut other_snooper = UnixStream::connect(socket_path.clone()).await.unwrap();
let mut other_snooper: AuthStream =
AsyncBincodeStream::from(&mut other_snooper).for_async();
let other_message = other_snooper.next().await.unwrap().unwrap();
assert_eq!(message, other_message);
let third_snooper_handle = tokio::spawn(async move {
let mut third_snooper = UnixStream::connect(socket_path.clone()).await.unwrap();
let mut third_snooper: AuthStream =
AsyncBincodeStream::from(&mut third_snooper).for_async();
// NOTE: Should hang
third_snooper.send(1234).await.unwrap()
});
sleep(Duration::from_millis(10)).await;
let server_handle = tokio::spawn(async move { server_authenticate(&mut server).await });
client_handle.await.unwrap().unwrap();
server_handle.await.unwrap().unwrap();
third_snooper_handle.abort();
}
#[tokio::test]
async fn test_dead_server() {
let (mut client, server) = UnixStream::pair().unwrap();
std::mem::drop(server);
let client_handle = tokio::spawn(async move {
let err = client_authenticate(&mut client, None).await;
assert_eq!(err, Err(ClientError::UnableToConnectToServer));
});
client_handle.await.unwrap();
}
#[tokio::test]
async fn test_no_response_from_server() {
let (mut client, server) = UnixStream::pair().unwrap();
let client_handle = tokio::spawn(async move {
let err = client_authenticate(&mut client, None).await;
assert_eq!(err, Err(ClientError::NoServerResponse));
});
sleep(Duration::from_millis(200)).await;
std::mem::drop(server);
client_handle.await.unwrap();
}
// TODO: Test challenge mismatch
// TODO: Test invoking server with junk data
}

5
src/server/command.rs
View File

@ -7,7 +7,6 @@ use clap::Parser;
use std::os::unix::net::UnixStream as StdUnixStream;
use tokio::net::UnixStream as TokioUnixStream;
use crate::core::bootstrap::authenticated_unix_socket;
use crate::core::common::UnixUser;
use crate::server::config::read_config_from_path_with_arg_overrides;
use crate::server::server_loop::listen_for_incoming_connections;
@ -53,8 +52,8 @@ pub async fn handle_command(
async fn socket_activate(config: ServerConfig) -> anyhow::Result<()> {
// TODO: allow getting socket path from other socket activation sources
let mut conn = get_socket_from_systemd().await?;
let uid = authenticated_unix_socket::server_authenticate(&mut conn).await?;
let conn = get_socket_from_systemd().await?;
let uid = conn.peer_cred()?.uid();
let unix_user = UnixUser::from_uid(uid.into())?;
handle_requests_for_single_session(conn, &unix_user, &config).await?;

12
src/server/server_loop.rs
View File

@ -9,7 +9,6 @@ use sqlx::MySqlConnection;
use crate::{
core::{
bootstrap::authenticated_unix_socket,
common::{UnixUser, DEFAULT_SOCKET_PATH},
protocol::request_response::{
create_server_to_client_message_stream, Request, Response, ServerToClientMessageStream,
@ -58,14 +57,9 @@ pub async fn listen_for_incoming_connections(
let listener = UnixListener::bind(socket_path)?;
while let Ok((mut conn, _addr)) = listener.accept().await {
let uid = match authenticated_unix_socket::server_authenticate(&mut conn).await {
Ok(uid) => uid,
Err(e) => {
eprintln!("Failed to authenticate client: {}", e);
conn.shutdown().await?;
continue;
}
};
let uid = conn.peer_cred()?.uid();
log::trace!("Accepted connection from uid {}", uid);
let unix_user = match UnixUser::from_uid(uid.into()) {
Ok(user) => user,
Err(e) => {