Ensure mount points writable before updating

The /boot and /boot/efi mount points may be read-only, so remount
them as read-write if necessary when writing.

src/bootupd.rs

@@ -3,6 +3,7 @@ use crate::coreos;
 use crate::efi;
 use crate::model::{ComponentStatus, ComponentUpdatable, ContentMetadata, SavedState, Status};
 use crate::{component, ipc};
+use crate::util;
 use anyhow::{anyhow, Context, Result};
 use serde::{Deserialize, Serialize};
 use std::borrow::Cow;
@@ -93,6 +94,10 @@ pub(crate) enum ComponentUpdateResult {
     },
 }
 
+fn ensure_writable_boot() -> Result<()> {
+    util::ensure_writable_mount("/boot")
+}
+
 /// daemon implementation of component update
 pub(crate) fn update(name: &str) -> Result<ComponentUpdateResult> {
     let mut state = SavedState::load_from_disk("/")?.unwrap_or_default();
@@ -109,6 +114,8 @@ pub(crate) fn update(name: &str) -> Result<ComponentUpdateResult> {
         _ => return Ok(ComponentUpdateResult::AtLatestVersion),
     };
 
+    ensure_writable_boot()?;
+
     let mut pending_container = state.pending.take().unwrap_or_default();
     let interrupted = pending_container.get(component.name()).cloned();
     pending_container.insert(component.name().into(), update.clone());
@@ -140,6 +147,9 @@ pub(crate) fn adopt_and_update(name: &str) -> Result<ContentMetadata> {
     if state.installed.get(name).is_some() {
         anyhow::bail!("Component {} is already installed", name);
     };
+
+    ensure_writable_boot()?;
+
     let update = if let Some(update) = component.query_update(&sysroot)? {
         update
     } else {

src/efi.rs

@@ -94,6 +94,7 @@ impl Component for EFI {
         let updatef = filetree::FileTree::new_from_dir(&updated).context("reading update dir")?;
         // For adoption, we should only touch files that we know about.
         let diff = updatef.relative_diff_to(&esp)?;
+        ensure_writable_efi()?;
         log::trace!("applying adoption diff: {}", &diff);
         filetree::apply_diff(&updated, &esp, &diff, None).context("applying filesystem changes")?;
         Ok(InstalledContent {
@@ -153,6 +154,7 @@ impl Component for EFI {
         let destdir = openat::Dir::open(&Path::new("/").join(MOUNT_PATH).join("EFI"))
             .context("opening EFI dir")?;
         validate_esp(&destdir)?;
+        ensure_writable_efi()?;
         log::trace!("applying diff: {}", &diff);
         filetree::apply_diff(&updated, &destdir, &diff, None)
             .context("applying filesystem changes")?;
@@ -280,3 +282,7 @@ fn validate_esp(dir: &openat::Dir) -> Result<()> {
     };
     Ok(())
 }
+
+fn ensure_writable_efi() -> Result<()> {
+    util::ensure_writable_mount(&Path::new("/").join(MOUNT_PATH))
+}

src/util.rs

@@ -4,6 +4,7 @@ use anyhow::{bail, Result};
 use openat_ext::OpenatDirExt;
 
 use std::process::Command;
+use std::path::Path;
 
 pub(crate) trait CommandRunExt {
     fn run(&mut self) -> Result<()>;
@@ -65,3 +66,20 @@ pub(crate) fn filenames(dir: &openat::Dir) -> Result<HashSet<String>> {
     }
     Ok(ret)
 }
+
+pub(crate) fn ensure_writable_mount<P: AsRef<Path>>(p: P) -> Result<()> {
+    use nix::sys::statvfs;
+    let p = p.as_ref();
+    let stat = statvfs::statvfs(p)?;
+    if !stat.flags().contains(statvfs::FsFlags::ST_RDONLY) {
+        return Ok(());
+    }
+    let status = std::process::Command::new("mount")
+        .args(&["-o", "remount,rw"])
+        .arg(p)
+        .status()?;
+    if !status.success() {
+        anyhow::bail!("Failed to remount {:?} writable", p);
+    }
+    Ok(())
+}