guest/compsvc/src/compos_key.rs

/*
 * Copyright 2022 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use anyhow::{bail, Context, Result};
use std::io::Write;
use std::process::{Command, Stdio};

const COMPOS_KEY_HELPER_PATH: &str = "/apex/com.android.compos/bin/compos_key_helper";

pub fn get_public_key() -> Result<Vec<u8>> {
    get_data_from_helper("public_key")
}

pub fn get_attestation_chain() -> Result<Vec<u8>> {
    get_data_from_helper("bcc")
}

fn get_data_from_helper(command: &str) -> Result<Vec<u8>> {
    let child = Command::new(COMPOS_KEY_HELPER_PATH)
        .arg(command)
        .stdin(Stdio::null())
        .stdout(Stdio::piped())
        .stderr(Stdio::piped())
        .spawn()?;
    let result = child.wait_with_output()?;
    if !result.status.success() {
        bail!("Helper failed: {:?}", result);
    }
    Ok(result.stdout)
}

pub fn sign(data: &[u8]) -> Result<Vec<u8>> {
    let mut child = Command::new(COMPOS_KEY_HELPER_PATH)
        .arg("sign")
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .stderr(Stdio::piped())
        .spawn()?;

    // No output is written until the entire input is consumed, so this shouldn't deadlock.
    let result =
        child.stdin.take().unwrap().write_all(data).context("Failed to write data to be signed");
    if result.is_ok() {
        let result = child.wait_with_output()?;
        if !result.status.success() {
            bail!("Helper failed: {}", result.status);
        }
        return Ok(result.stdout);
    }

    // The child may have exited already, but if it hasn't then we need to make sure it does.
    let _ignored = child.kill();

    let result = result.with_context(|| match child.wait() {
        Ok(exit_status) => format!("Child exited: {}", exit_status),
        Err(wait_err) => format!("Wait for child failed: {:?}", wait_err),
    });
    Err(result.unwrap_err())
}