compos/src/pvm_exec.rs

/*
 * Copyright (C) 2021 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.
 */

//! pvm_exec is a proxy/wrapper command to run a command remotely. It does not transport the
//! program and just pass the command line arguments to compsvc to execute. The most important task
//! for this program is to run a `fd_server` that serves remote file read/write requests.
//!
//! Example:
//! $ adb shell exec 3</dev/zero 4<>/dev/null pvm_exec --in-fd 3 --out-fd 4 -- sleep 10
//!
//! Note the immediate argument right after "--" (e.g. "sleep" in the example above) is not really
//! used. It is only for ergonomics.

use anyhow::{bail, Context, Result};
use log::{error, warn};
use minijail::Minijail;
use nix::fcntl::{fcntl, FcntlArg::F_GETFD};
use nix::sys::stat::fstat;
use std::os::unix::io::RawFd;
use std::path::Path;
use std::process::exit;

use compos_aidl_interface::aidl::com::android::compos::{
    ICompService::ICompService, InputFdAnnotation::InputFdAnnotation, Metadata::Metadata,
    OutputFdAnnotation::OutputFdAnnotation,
};
use compos_aidl_interface::binder::Strong;

static SERVICE_NAME: &str = "compsvc";
static FD_SERVER_BIN: &str = "/apex/com.android.virt/bin/fd_server";

fn get_local_service() -> Strong<dyn ICompService> {
    compos_aidl_interface::binder::get_interface(SERVICE_NAME).expect("Cannot reach compsvc")
}

fn spawn_fd_server(metadata: &Metadata, debuggable: bool) -> Result<Minijail> {
    let mut inheritable_fds = if debuggable {
        vec![1, 2] // inherit/redirect stdout/stderr for debugging
    } else {
        vec![]
    };

    let mut args = vec![FD_SERVER_BIN.to_string()];
    for metadata in &metadata.input_fd_annotations {
        args.push("--ro-fds".to_string());
        args.push(metadata.fd.to_string());
        inheritable_fds.push(metadata.fd);
    }
    for metadata in &metadata.output_fd_annotations {
        args.push("--rw-fds".to_string());
        args.push(metadata.fd.to_string());
        inheritable_fds.push(metadata.fd);
    }

    let jail = Minijail::new()?;
    let _pid = jail.run(Path::new(FD_SERVER_BIN), &inheritable_fds, &args)?;
    Ok(jail)
}

fn is_fd_valid(fd: RawFd) -> Result<bool> {
    let retval = fcntl(fd, F_GETFD)?;
    Ok(retval >= 0)
}

fn parse_arg_fd(arg: &str) -> Result<RawFd> {
    let fd = arg.parse::<RawFd>()?;
    if !is_fd_valid(fd)? {
        bail!("Bad FD: {}", fd);
    }
    Ok(fd)
}

struct Config {
    args: Vec<String>,
    metadata: Metadata,
    debuggable: bool,
}

fn parse_args() -> Result<Config> {
    #[rustfmt::skip]
    let matches = clap::App::new("pvm_exec")
        .arg(clap::Arg::with_name("in-fd")
             .long("in-fd")
             .takes_value(true)
             .multiple(true)
             .use_delimiter(true))
        .arg(clap::Arg::with_name("out-fd")
             .long("out-fd")
             .takes_value(true)
             .multiple(true)
             .use_delimiter(true))
        .arg(clap::Arg::with_name("debug")
             .long("debug"))
        .arg(clap::Arg::with_name("args")
             .last(true)
             .required(true)
             .multiple(true))
        .get_matches();

    let results: Result<Vec<_>> = matches
        .values_of("in-fd")
        .unwrap_or_default()
        .map(|arg| {
            let fd = parse_arg_fd(arg)?;
            let file_size = fstat(fd)?.st_size;
            Ok(InputFdAnnotation { fd, file_size })
        })
        .collect();
    let input_fd_annotations = results?;

    let results: Result<Vec<_>> = matches
        .values_of("out-fd")
        .unwrap_or_default()
        .map(|arg| {
            let fd = parse_arg_fd(arg)?;
            Ok(OutputFdAnnotation { fd })
        })
        .collect();
    let output_fd_annotations = results?;

    let args: Vec<_> = matches.values_of("args").unwrap().map(|s| s.to_string()).collect();
    let debuggable = matches.is_present("debug");

    Ok(Config {
        args,
        metadata: Metadata { input_fd_annotations, output_fd_annotations },
        debuggable,
    })
}

fn main() -> Result<()> {
    // 1. Parse the command line arguments for collect execution data.
    let Config { args, metadata, debuggable } = parse_args()?;

    // 2. Spawn and configure a fd_server to serve remote read/write requests.
    let fd_server_jail = spawn_fd_server(&metadata, debuggable)?;
    let fd_server_lifetime = scopeguard::guard(fd_server_jail, |fd_server_jail| {
        if let Err(e) = fd_server_jail.kill() {
            if !matches!(e, minijail::Error::Killed(_)) {
                warn!("Failed to kill fd_server: {}", e);
            }
        }
    });

    // 3. Send the command line args to the remote to execute.
    let exit_code = get_local_service().execute(&args, &metadata).context("Binder call failed")?;

    // Be explicit about the lifetime, which should last at least until the task is finished.
    drop(fd_server_lifetime);

    if exit_code > 0 {
        error!("remote execution failed with exit code {}", exit_code);
        exit(exit_code as i32);
    }
    Ok(())
}