lib.rs

//! Mount helpers for bootc-initramfs

use std::{
    ffi::OsString,
    fmt::Debug,
    io::ErrorKind,
    os::fd::{AsFd, AsRawFd, OwnedFd},
    path::{Path, PathBuf},
};

use anyhow::{Context, Result};
use clap::Parser;
use rustix::{
    fs::{CWD, Mode, OFlags, major, minor, mkdirat, openat, stat, symlink},
    io::Errno,
    mount::{
        FsMountFlags, MountAttrFlags, OpenTreeFlags, UnmountFlags, fsconfig_create,
        fsconfig_set_string, fsmount, open_tree, unmount,
    },
    path,
};
use serde::Deserialize;

use cfsctl::composefs;
use cfsctl::composefs_boot;
use composefs::{
    fsverity::{FsVerityHashValue, Sha512HashValue},
    mount::FsHandle,
    mountcompat::{overlayfs_set_fd, overlayfs_set_lower_and_data_fds, prepare_mount},
    repository::Repository,
};
use composefs_boot::cmdline::get_cmdline_composefs;

use fn_error_context::context;

use bootc_kernel_cmdline::utf8::Cmdline;

// mount_setattr syscall support
const MOUNT_ATTR_RDONLY: u64 = 0x00000001;

#[repr(C)]
struct MountAttr {
    attr_set: u64,
    attr_clr: u64,
    propagation: u64,
    userns_fd: u64,
}

/// Set mount attributes using mount_setattr syscall
#[context("Setting mount attributes")]
#[allow(unsafe_code)]
fn mount_setattr(fd: impl AsFd, flags: libc::c_int, attr: &MountAttr) -> Result<()> {
    let ret = unsafe {
        libc::syscall(
            libc::SYS_mount_setattr,
            fd.as_fd().as_raw_fd(),
            c"".as_ptr(),
            flags,
            attr as *const MountAttr,
            std::mem::size_of::<MountAttr>(),
        )
    };
    if ret == -1 {
        Err(std::io::Error::last_os_error())?;
    }
    Ok(())
}

/// Set mount to readonly
#[context("Setting mount readonly")]
fn set_mount_readonly(fd: impl AsFd) -> Result<()> {
    let attr = MountAttr {
        attr_set: MOUNT_ATTR_RDONLY,
        attr_clr: 0,
        propagation: 0,
        userns_fd: 0,
    };
    mount_setattr(fd, libc::AT_EMPTY_PATH, &attr)
}

/// Types of mounts supported by the configuration
#[derive(Clone, Copy, Debug, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum MountType {
    /// No mount
    None,
    /// Bind mount
    Bind,
    /// Overlay mount
    Overlay,
    /// Transient mount
    Transient,
}

#[derive(Debug, Default, Deserialize)]
struct RootConfig {
    #[serde(default)]
    transient: bool,
}

/// Configuration for mount operations
#[derive(Debug, Default, Deserialize)]
pub struct MountConfig {
    /// The type of mount to use
    pub mount: Option<MountType>,
    #[serde(default)]
    /// Whether this mount should be transient (temporary)
    pub transient: bool,
}

#[derive(Deserialize, Default)]
struct Config {
    #[serde(default)]
    etc: MountConfig,
    #[serde(default)]
    var: MountConfig,
    #[serde(default)]
    root: RootConfig,
}

/// Command-line arguments
#[derive(Parser, Debug)]
#[command(version)]
pub struct Args {
    #[arg(help = "Execute this command (for testing)")]
    /// Execute this command (for testing)
    pub cmd: Vec<OsString>,

    #[arg(
        long,
        default_value = "/sysroot",
        help = "sysroot directory in initramfs"
    )]
    /// sysroot directory in initramfs
    pub sysroot: PathBuf,

    #[arg(
        long,
        default_value = "/usr/lib/composefs/setup-root-conf.toml",
        help = "Config path (for testing)"
    )]
    /// Config path (for testing)
    pub config: PathBuf,

    // we want to test in a userns, but can't mount erofs there
    #[arg(long, help = "Bind mount root-fs from (for testing)")]
    /// Bind mount root-fs from (for testing)
    pub root_fs: Option<PathBuf>,

    #[arg(long, help = "Kernel commandline args (for testing)")]
    /// Kernel commandline args (for testing)
    pub cmdline: Option<Cmdline<'static>>,

    #[arg(long, help = "Mountpoint (don't replace sysroot, for testing)")]
    /// Mountpoint (don't replace sysroot, for testing)
    pub target: Option<PathBuf>,
}

/// Wrapper around [`composefs::mount::mount_at`]
pub fn mount_at_wrapper(
    fs_fd: impl AsFd,
    dirfd: impl AsFd,
    path: impl path::Arg + Debug + Clone,
) -> Result<()> {
    composefs::mount::mount_at(fs_fd, dirfd, path.clone())
        .with_context(|| format!("Mounting at path {path:?}"))
}

/// Wrapper around [`rustix::fs::openat`]
#[context("Opening dir {name:?}")]
pub fn open_dir(dirfd: impl AsFd, name: impl AsRef<Path> + Debug) -> Result<OwnedFd> {
    let res = openat(
        dirfd,
        name.as_ref(),
        OFlags::PATH | OFlags::DIRECTORY | OFlags::CLOEXEC,
        Mode::empty(),
    );

    Ok(res?)
}

#[context("Ensure dir")]
fn ensure_dir(dirfd: impl AsFd, name: &str, mode: Option<rustix::fs::Mode>) -> Result<OwnedFd> {
    match mkdirat(dirfd.as_fd(), name, mode.unwrap_or(0o700.into())) {
        Ok(()) | Err(Errno::EXIST) => {}
        Err(err) => Err(err).with_context(|| format!("Creating dir {name}"))?,
    }

    open_dir(dirfd, name)
}

#[context("Bind mounting to path {path}")]
fn bind_mount(fd: impl AsFd, path: &str) -> Result<OwnedFd> {
    let res = open_tree(
        fd.as_fd(),
        path,
        OpenTreeFlags::OPEN_TREE_CLONE
            | OpenTreeFlags::OPEN_TREE_CLOEXEC
            | OpenTreeFlags::AT_EMPTY_PATH,
    );

    Ok(res?)
}

#[context("Mounting tmpfs")]
fn mount_tmpfs() -> Result<OwnedFd> {
    let tmpfs = FsHandle::open("tmpfs")?;
    fsconfig_create(tmpfs.as_fd())?;
    Ok(fsmount(
        tmpfs.as_fd(),
        FsMountFlags::FSMOUNT_CLOEXEC,
        MountAttrFlags::empty(),
    )?)
}

#[context("Mounting state as overlay")]
fn overlay_state(
    base: impl AsFd,
    state: impl AsFd,
    source: &str,
    mode: Option<rustix::fs::Mode>,
    mount_attr_flags: Option<MountAttrFlags>,
) -> Result<()> {
    let upper = ensure_dir(state.as_fd(), "upper", mode)?;
    let work = ensure_dir(state.as_fd(), "work", mode)?;

    let overlayfs = FsHandle::open("overlay")?;
    fsconfig_set_string(overlayfs.as_fd(), "source", source)?;
    overlayfs_set_fd(overlayfs.as_fd(), "workdir", work.as_fd())?;
    overlayfs_set_fd(overlayfs.as_fd(), "upperdir", upper.as_fd())?;
    overlayfs_set_lower_and_data_fds(&overlayfs, base.as_fd(), None::<OwnedFd>)?;
    fsconfig_create(overlayfs.as_fd())?;
    let fs = fsmount(
        overlayfs.as_fd(),
        FsMountFlags::FSMOUNT_CLOEXEC,
        mount_attr_flags.unwrap_or(MountAttrFlags::empty()),
    )?;

    mount_at_wrapper(fs, base, ".").context("Moving mount")
}

/// Mounts a transient overlayfs with passed in fd as the lowerdir
#[context("Mounting transient overlayfs")]
pub fn overlay_transient(
    base: impl AsFd,
    mode: Option<rustix::fs::Mode>,
    mount_attr_flags: Option<MountAttrFlags>,
) -> Result<()> {
    overlay_state(
        base,
        prepare_mount(mount_tmpfs()?)?,
        "transient",
        mode,
        mount_attr_flags,
    )
}

#[context("Opening rootfs")]
fn open_root_fs(path: &Path) -> Result<OwnedFd> {
    let rootfs = open_tree(
        CWD,
        path,
        OpenTreeFlags::OPEN_TREE_CLONE | OpenTreeFlags::OPEN_TREE_CLOEXEC,
    )?;

    set_mount_readonly(&rootfs)?;

    Ok(rootfs)
}

/// Prepares a floating mount for composefs and returns the fd
///
/// # Arguments
/// * sysroot                - fd for /sysroot
/// * name                   - Name of the EROFS image to be mounted
/// * allow_missing_fsverity - Whether to allow mount without fsverity support
#[context("Mounting composefs image")]
pub fn mount_composefs_image(
    sysroot: &OwnedFd,
    name: &str,
    allow_missing_fsverity: bool,
) -> Result<OwnedFd> {
    let mut repo = Repository::<Sha512HashValue>::open_path(sysroot, "composefs")?;
    repo.set_insecure(allow_missing_fsverity);
    let rootfs = repo
        .mount(name)
        .context("Failed to mount composefs image")?;

    set_mount_readonly(&rootfs)?;

    Ok(rootfs)
}

/// Mounts a subdirectory with the specified configuration
#[context("Mounting subdirectory")]
pub fn mount_subdir(
    new_root: impl AsFd,
    state: impl AsFd,
    subdir: &str,
    config: MountConfig,
    default: MountType,
) -> Result<()> {
    let mount_type = match config.mount {
        Some(mt) => mt,
        None => match config.transient {
            true => MountType::Transient,
            false => default,
        },
    };

    match mount_type {
        MountType::None => Ok(()),
        MountType::Bind => Ok(mount_at_wrapper(
            bind_mount(&state, subdir)?,
            &new_root,
            subdir,
        )?),
        MountType::Overlay => overlay_state(
            open_dir(&new_root, subdir)?,
            open_dir(&state, subdir)?,
            "overlay",
            None,
            None,
        ),
        MountType::Transient => overlay_transient(open_dir(&new_root, subdir)?, None, None),
    }
}

#[context("GPT workaround")]
/// Workaround for /dev/gpt-auto-root
pub fn gpt_workaround() -> Result<()> {
    // https://github.com/systemd/systemd/issues/35017
    let rootdev = stat("/dev/gpt-auto-root");

    let rootdev = match rootdev {
        Ok(r) => r,
        Err(e) if e.kind() == ErrorKind::NotFound => return Ok(()),
        Err(e) => Err(e)?,
    };

    let target = format!(
        "/dev/block/{}:{}",
        major(rootdev.st_rdev),
        minor(rootdev.st_rdev)
    );
    symlink(target, "/run/systemd/volatile-root")?;
    Ok(())
}

/// Sets up /sysroot for switch-root
#[context("Setting up /sysroot")]
pub fn setup_root(args: Args) -> Result<()> {
    let config = match std::fs::read_to_string(args.config) {
        Ok(text) => toml::from_str(&text)?,
        Err(err) if err.kind() == ErrorKind::NotFound => Config::default(),
        Err(err) => Err(err)?,
    };

    let sysroot = open_dir(CWD, &args.sysroot)
        .with_context(|| format!("Failed to open sysroot {:?}", args.sysroot))?;

    let cmdline = args
        .cmdline
        .unwrap_or(Cmdline::from_proc().context("Failed to read cmdline")?);

    let (image, insecure) = get_cmdline_composefs::<Sha512HashValue>(&cmdline)?;

    let new_root = match args.root_fs {
        Some(path) => open_root_fs(&path).context("Failed to clone specified root fs")?,
        None => mount_composefs_image(&sysroot, &image.to_hex(), insecure)?,
    };

    // we need to clone this before the next step to make sure we get the old one
    let sysroot_clone = bind_mount(&sysroot, "")?;

    set_mount_readonly(&sysroot_clone)?;

    let mount_target = args.target.unwrap_or(args.sysroot.clone());

    // Ideally we build the new root filesystem together before we mount it, but that only works on
    // 6.15 and later.  Before 6.15 we can't mount into a floating tree, so mount it first.  This
    // will leave an abandoned clone of the sysroot mounted under it, but that's OK for now.
    if cfg!(feature = "pre-6.15") {
        mount_at_wrapper(&new_root, CWD, &mount_target)?;
    }

    if config.root.transient {
        overlay_transient(&new_root, None, None)?;
    }

    match composefs::mount::mount_at(&sysroot_clone, &new_root, "sysroot") {
        Ok(()) | Err(Errno::NOENT) => {}
        Err(err) => Err(err)?,
    }

    // etc + var
    let state = open_dir(open_dir(&sysroot, "state/deploy")?, image.to_hex())?;
    mount_subdir(&new_root, &state, "etc", config.etc, MountType::Bind)?;
    mount_subdir(&new_root, &state, "var", config.var, MountType::Bind)?;

    if cfg!(not(feature = "pre-6.15")) {
        // Replace the /sysroot with the new composed root filesystem
        unmount(&args.sysroot, UnmountFlags::DETACH)?;
        mount_at_wrapper(&new_root, CWD, &mount_target)?;
    }

    Ok(())
}