Create protected boot aliases after initramfs build

1 files changed, 28 insertions, 1 deletions

diff --git a/src/initramfs.rs b/src/initramfs.rs
index ca1063d..4475aed 100644
--- a/src/initramfs.rs
+++ b/src/initramfs.rs
@@ -1,5 +1,6 @@
 use std::ffi::OsString;
 use std::fs;
+use std::os::unix::fs::symlink;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 
@@ -171,10 +172,36 @@ impl<R: CommandRunner> InitramfsBuilder for MakeInitrdBuilder<R> {
                 request.kernel().as_str().into(),
             ],
         ))?;
-        InitramfsResult::from_rootfs(request.rootfs(), request.kernel())
+        let result = InitramfsResult::from_rootfs(request.rootfs(), request.kernel())?;
+        write_boot_alias(
+            request.rootfs(),
+            "vmlinuz",
+            Path::new(&format!("vmlinuz-{}", request.kernel().as_str())),
+        )?;
+        write_boot_alias(
+            request.rootfs(),
+            "initrd.img",
+            Path::new(result.initrd_path().file_name().expect("initrd filename")),
+        )?;
+        Ok(result)
     }
 }
 
+/// Set a conventional boot alias without ever following or replacing a
+/// pre-existing non-symlink filesystem entry.
+fn write_boot_alias(rootfs: &Path, alias: &str, target: &Path) -> Result<()> {
+    let path = rootfs.join("boot").join(alias);
+    match fs::symlink_metadata(&path) {
+        Ok(metadata) if metadata.file_type().is_symlink() => {
+            fs::remove_file(&path).with_context(|| format!("remove existing boot alias {}", path.display()))?;
+        }
+        Ok(_) => bail!("refusing to replace non-symlink boot alias: {}", path.display()),
+        Err(error) if error.kind() == std::io::ErrorKind::NotFound => {}
+        Err(error) => return Err(error).with_context(|| format!("inspect boot alias {}", path.display())),
+    }
+    symlink(target, &path).with_context(|| format!("create boot alias {}", path.display()))
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct InitramfsResult {
     initrd_path: PathBuf,