virtiofs: Set SELinux context on readonly mounts

Apply system_u:object_r:usr_t:s0 context to readonly virtiofs mounts
to avoid SELinux denials when accessing them as container storage.
This allows readonly bind mounts to work correctly with podman.

The function was renamed from generate_mount_unit to
generate_virtiofs_mount_unit for clarity.

Assisted-by: Claude Code (Sonnet 4.5)
Signed-off-by: Colin Walters <walters@verbum.org>

Author: cgwalters

crates/kit/src/credentials.rs

@@ -45,8 +45,19 @@ pub fn guest_path_to_unit_name(guest_path: &str) -> String {
 /// Note: systemd automatically creates mount point directories, so DirectoryMode is not needed
 ///
 /// Returns the complete unit file content as a string
-pub fn generate_mount_unit(virtiofs_tag: &str, guest_path: &str, readonly: bool) -> String {
-    let options = if readonly { "Options=ro" } else { "Options=rw" };
+pub fn generate_virtiofs_mount_unit(
+    virtiofs_tag: &str,
+    guest_path: &str,
+    readonly: bool,
+) -> String {
+    let options = if readonly {
+        // Default readonly mounts to usr_t - this helps avoid SELinux
+        // issues when accessing them as container storage for example.
+        // TODO don't hardcode this, detect from the environment
+        "ro,context=system_u:object_r:usr_t:s0"
+    } else {
+        "rw"
+    };
 
     format!(
         "[Unit]\n\
@@ -61,7 +72,7 @@ pub fn generate_mount_unit(virtiofs_tag: &str, guest_path: &str, readonly: bool)
          What={tag}\n\
          Where={path}\n\
          Type=virtiofs\n\
-         {options}\n",
+         Options={options}\n",
         tag = virtiofs_tag,
         path = guest_path,
         options = options
@@ -82,7 +93,7 @@ pub fn smbios_creds_for_mount_unit(
     readonly: bool,
 ) -> Result<Vec<String>> {
     let unit_name = guest_path_to_unit_name(guest_path);
-    let mount_unit_content = generate_mount_unit(virtiofs_tag, guest_path, readonly);
+    let mount_unit_content = generate_virtiofs_mount_unit(virtiofs_tag, guest_path, readonly);
     let encoded_mount = data_encoding::BASE64.encode(mount_unit_content.as_bytes());
 
     let mount_cred =

crates/kit/src/libvirt/run.rs

@@ -882,8 +882,11 @@ fn process_bind_mounts(
 
         // Generate SMBIOS credential for mount unit (without dropin)
         let unit_name = crate::credentials::guest_path_to_unit_name(&bind_mount.guest_path);
-        let mount_unit_content =
-            crate::credentials::generate_mount_unit(&tag, &bind_mount.guest_path, readonly);
+        let mount_unit_content = crate::credentials::generate_virtiofs_mount_unit(
+            &tag,
+            &bind_mount.guest_path,
+            readonly,
+        );
         let encoded_mount = data_encoding::BASE64.encode(mount_unit_content.as_bytes());
         let mount_cred =
             format!("io.systemd.credential.binary:systemd.extra-unit.{unit_name}={encoded_mount}");
@@ -1211,7 +1214,7 @@ fn create_libvirt_domain_from_disk(
         let guest_mount_path = "/run/host-container-storage";
         let unit_name = crate::credentials::guest_path_to_unit_name(guest_mount_path);
         let mount_unit_content =
-            crate::credentials::generate_mount_unit("hoststorage", guest_mount_path, true);
+            crate::credentials::generate_virtiofs_mount_unit("hoststorage", guest_mount_path, true);
         let encoded_mount = data_encoding::BASE64.encode(mount_unit_content.as_bytes());
         let mount_cred =
             format!("io.systemd.credential.binary:systemd.extra-unit.{unit_name}={encoded_mount}");

crates/kit/src/run_ephemeral.rs

@@ -915,7 +915,7 @@ pub(crate) async fn run_impl(opts: RunEphemeralOpts) -> Result<()> {
             let mount_point = format!("/run/virtiofs-mnt-{}", mount_name_str);
             let unit_name = crate::credentials::guest_path_to_unit_name(&mount_point);
             let mount_unit_content =
-                crate::credentials::generate_mount_unit(&tag, &mount_point, is_readonly);
+                crate::credentials::generate_virtiofs_mount_unit(&tag, &mount_point, is_readonly);
             let encoded_mount = data_encoding::BASE64.encode(mount_unit_content.as_bytes());
 
             // Create SMBIOS credential for the mount unit