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Stop if /dev is not a bind mount with loopback #431

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Apr 2, 2024
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3 changes: 3 additions & 0 deletions lib/src/install.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1177,6 +1177,9 @@ pub(crate) async fn install_to_disk(mut opts: InstallToDiskOpts) -> Result<()> {
block_opts.device
);
}
if !crate::mount::is_same_as_host(Utf8Path::new("/dev"))? {
anyhow::bail!("Loopback mounts (--via-loopback) require host devices (-v /dev:/dev)");
}
} else if !target_blockdev_meta.file_type().is_block_device() {
anyhow::bail!("Not a block device: {}", block_opts.device);
}
Expand Down
22 changes: 22 additions & 0 deletions lib/src/mount.rs
Original file line number Diff line number Diff line change
Expand Up @@ -57,3 +57,25 @@ pub(crate) fn mount(dev: &str, target: &Utf8Path) -> Result<()> {
[dev, target.as_str()],
)
}

/// If the fsid of the passed path matches the fsid of the same path rooted
/// at /proc/1/root, it is assumed that these are indeed the same mounted
/// filesystem between container and host.
/// Path should be absolute.
#[context("Comparing filesystems at {path} and /proc/1/root/{path}")]
pub(crate) fn is_same_as_host(path: &Utf8Path) -> Result<bool> {
// Add a leading '/' in case a relative path is passed
let path = Utf8Path::new("/").join(path);

// Using statvfs instead of fs, since rustix will translate the fsid field
// for us.
let devstat = rustix::fs::statvfs(path.as_std_path())?;
let hostpath = Utf8Path::new("/proc/1/root").join(path.strip_prefix("/")?);
let hostdevstat = rustix::fs::statvfs(hostpath.as_std_path())?;
tracing::trace!(
"base mount id {:?}, host mount id {:?}",
devstat.f_fsid,
hostdevstat.f_fsid
);
Ok(devstat.f_fsid == hostdevstat.f_fsid)
}