libeos-updater-util: Add method to detect if /boot is an automount

On some hosts, systemd sets up `/boot` as an autofs automount. Unfortunately, this configuration has some bugs that make usage of `/boot` less than robust. Add a method to see if `/boot` is an automount. This uses libmount to parse `/proc/self/mountinfo` and check if the first mountpoint for the sysroot's boot directory has the `autofs` filesystem type. libmount version 2.24 was chosen as a minimum because that's when `libmnt_table` and `libmnt_cache` reference counting was added. https://phabricator.endlessm.com/T33136 (cherry picked from commit 7538608)
endlessm · Mar 11, 2022 · 5019318 · 5019318
1 parent 36b4fb6
commit 5019318
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diff --git a/debian/control b/debian/control
@@ -22,6 +22,7 @@ Build-Depends:
  libgsystem-dev,
  libjson-glib-dev (>= 1.2.6-1endless2),
  libmogwai-schedule-client-0-dev,
+ libmount-dev (>= 2.24),
  libnm-dev (>= 1.2.0),
  libostree-dev (>= 2017.12),
  libsoup2.4-dev,

diff --git a/libeos-updater-util/meson.build b/libeos-updater-util/meson.build
@@ -36,6 +36,7 @@ libeos_updater_util_deps = [
   dependency('gobject-2.0', version: '>= 2.62'),
   dependency('json-glib-1.0', version: '>= 1.2.6'),
   dependency('libsoup-2.4'),
+  dependency('mount', version: '>= 2.24'),
   dependency('ostree-1', version: '>= 2018.6'),
 ]
 

diff --git a/libeos-updater-util/ostree-util.c b/libeos-updater-util/ostree-util.c
@@ -23,6 +23,7 @@
 #include <glib.h>
 #include <libeos-updater-util/ostree-util.h>
 #include <libeos-updater-util/util.h>
+#include <libmount.h>
 #include <libsoup/soup.h>
 #include <ostree.h>
 #include <string.h>
@@ -311,3 +312,79 @@ eos_updater_get_ostree_path (OstreeRepo *repo,
   *ostree_path = g_steal_pointer (&path);
   return TRUE;
 }
+
+/**
+ * eos_updater_sysroot_boot_is_automount:
+ * @sysroot: loaded OSTree sysroot to use
+ * @mountinfo: (nullable): path to mountinfo file
+ *
+ * Find if the boot directory in @sysroot is an automount mount. The first
+ * mountpoint for the boot directory in @mountinfo is found. If the filesystem
+ * type for the mountpoint is autofs, then the boot directory is automounted.
+ *
+ * If @mountinfo is %NULL, /proc/self/mountinfo is used.
+ *
+ * Returns: %TRUE if boot is an automount
+ */
+gboolean
+eos_updater_sysroot_boot_is_automount (OstreeSysroot *sysroot,
+                                       const gchar   *mountinfo)
+{
+  GFile *sysroot_file;
+  g_autoptr(GFile) boot_file = NULL;
+  g_autofree gchar *boot_path = NULL;
+  gboolean ret = FALSE;
+  struct libmnt_table *tb = NULL;
+  struct libmnt_cache *cache;
+  struct libmnt_fs *fs;
+
+  sysroot_file = ostree_sysroot_get_path (sysroot);
+  boot_file = g_file_get_child (sysroot_file, "boot");
+  boot_path = g_file_get_path (boot_file);
+  if (boot_path == NULL)
+    {
+      g_autofree gchar *sysroot_path = g_file_get_path (sysroot_file);
+      g_warning ("No boot directory in sysroot %s", sysroot_path);
+      goto out;
+    }
+
+  if (mountinfo == NULL)
+    mountinfo = "/proc/self/mountinfo";
+  tb = mnt_new_table_from_file (mountinfo);
+  if (tb == NULL)
+    {
+      g_warning ("Failed to parse %s: %s", mountinfo, g_strerror (errno));
+      goto out;
+    }
+
+  cache = mnt_new_cache ();
+  if (cache == NULL)
+    {
+      g_warning ("Failed to create libmount cache: %s", g_strerror (errno));
+      goto out;
+    }
+  mnt_table_set_cache (tb, cache);
+  mnt_unref_cache (cache);
+
+  /* Find the /boot mountpoint iterating forward so that the autofs mount is
+   * found and not the automount target filesystem, as the autofs mount is
+   * listed first in mountinfo.
+   */
+  fs = mnt_table_find_mountpoint (tb, boot_path, MNT_ITER_FORWARD);
+  if (fs == NULL)
+    {
+      g_warning ("Failed to find mountpoint for %s: %s", boot_path,
+                 g_strerror (errno));
+      goto out;
+    }
+
+  ret = g_strcmp0 (mnt_fs_get_fstype (fs), "autofs") == 0;
+  g_debug ("Boot directory %s is%s on an autofs filesystem",
+           boot_path, ret ? "" : " not");
+
+ out:
+  if (tb != NULL)
+    mnt_unref_table (tb);
+
+  return ret;
+}
diff --git a/libeos-updater-util/ostree-util.h b/libeos-updater-util/ostree-util.h
@@ -47,4 +47,7 @@ gboolean eos_updater_get_ostree_path (OstreeRepo *repo,
                                       gchar **ostree_path,
                                       GError **error);
 
+gboolean eos_updater_sysroot_boot_is_automount (OstreeSysroot *sysroot,
+                                                const gchar   *mountinfo);
+
 G_END_DECLS
diff --git a/libeos-updater-util/tests/ostree-util.c b/libeos-updater-util/tests/ostree-util.c
@@ -147,6 +147,85 @@ test_ostree_no_deployments (Fixture       *fixture,
   g_assert_cmpuint (commit_timestamp, ==, 0);
 }
 
+static void
+test_ostree_sysroot_boot_automount (Fixture       *fixture,
+                                    gconstpointer  user_data G_GNUC_UNUSED)
+{
+  g_autoptr(GError) error = NULL;
+  gboolean retval;
+  GFile *sysroot_file = ostree_sysroot_get_path (fixture->sysroot);
+  g_autofree gchar *sysroot_path = g_file_get_path (sysroot_file);
+  g_autoptr(GFile) boot_file = g_file_get_child (sysroot_file, "boot");
+  g_autofree gchar *boot_path = g_file_get_path (boot_file);
+  g_autoptr(GFile) mountinfo_file = g_file_get_child (fixture->tmp_dir,
+                                                      "mountinfo");
+  g_autofree gchar *mountinfo_path = g_file_get_path (mountinfo_file);
+  g_autofree gchar *mountinfo_contents = NULL;
+
+  retval = g_file_make_directory (boot_file, NULL, &error);
+  g_assert_no_error (error);
+  g_assert_true (retval);
+
+  /* No separate /boot mount */
+  g_clear_pointer (&mountinfo_contents, g_free);
+  mountinfo_contents =
+    g_strdup_printf ("1 1 1:1 / %s rw - ext4 /dev/sda1 rw\n", sysroot_path);
+  g_test_message ("boot %s, mountinfo:\n%s", boot_path, mountinfo_contents);
+  retval = g_file_replace_contents (mountinfo_file, mountinfo_contents,
+                                    strlen (mountinfo_contents), NULL, FALSE,
+                                    G_FILE_CREATE_NONE, NULL, NULL, &error);
+  g_assert_no_error (error);
+  g_assert_true (retval);
+  retval = eos_updater_sysroot_boot_is_automount (fixture->sysroot, mountinfo_path);
+  g_assert_false (retval);
+
+  /* Non-automount /boot */
+  g_clear_pointer (&mountinfo_contents, g_free);
+  mountinfo_contents =
+    g_strdup_printf ("1 1 1:2 / %s rw - ext4 /dev/sda2 rw\n"
+                     "2 1 1:1 / %s rw - ext4 /dev/sda1 rw\n",
+                     sysroot_path, boot_path);
+  g_test_message ("boot %s, mountinfo:\n%s", boot_path, mountinfo_contents);
+  retval = g_file_replace_contents (mountinfo_file, mountinfo_contents,
+                                    strlen (mountinfo_contents), NULL, FALSE,
+                                    G_FILE_CREATE_NONE, NULL, NULL, &error);
+  g_assert_no_error (error);
+  g_assert_true (retval);
+  retval = eos_updater_sysroot_boot_is_automount (fixture->sysroot, mountinfo_path);
+  g_assert_false (retval);
+
+  /* Automount /boot without target mount */
+  g_clear_pointer (&mountinfo_contents, g_free);
+  mountinfo_contents =
+    g_strdup_printf ("1 1 1:2 / %s rw - ext4 /dev/sda2 rw\n"
+                     "2 1 0:1 / %s rw - autofs systemd-1 rw\n",
+                     sysroot_path, boot_path);
+  g_test_message ("boot %s, mountinfo:\n%s", boot_path, mountinfo_contents);
+  retval = g_file_replace_contents (mountinfo_file, mountinfo_contents,
+                                    strlen (mountinfo_contents), NULL, FALSE,
+                                    G_FILE_CREATE_NONE, NULL, NULL, &error);
+  g_assert_no_error (error);
+  g_assert_true (retval);
+  retval = eos_updater_sysroot_boot_is_automount (fixture->sysroot, mountinfo_path);
+  g_assert_true (retval);
+
+  /* Automount /boot with target mount */
+  g_clear_pointer (&mountinfo_contents, g_free);
+  mountinfo_contents =
+    g_strdup_printf ("1 1 1:2 / %s rw - ext4 /dev/sda2 rw\n"
+                     "2 1 0:1 / %s rw - autofs systemd-1 rw\n"
+                     "3 2 1:1 / %s rw - vfat /dev/sda1 rw\n",
+                     sysroot_path, boot_path, boot_path);
+  g_test_message ("boot %s, mountinfo:\n%s", boot_path, mountinfo_contents);
+  retval = g_file_replace_contents (mountinfo_file, mountinfo_contents,
+                                    strlen (mountinfo_contents), NULL, FALSE,
+                                    G_FILE_CREATE_NONE, NULL, NULL, &error);
+  g_assert_no_error (error);
+  g_assert_true (retval);
+  retval = eos_updater_sysroot_boot_is_automount (fixture->sysroot, mountinfo_path);
+  g_assert_true (retval);
+}
+
 int
 main (int   argc,
       char *argv[])
@@ -157,6 +236,8 @@ main (int   argc,
 
   g_test_add ("/ostree/no-deployments", Fixture, NULL, setup,
               test_ostree_no_deployments, teardown);
+  g_test_add ("/ostree/sysroot-boot-automount", Fixture, NULL, setup,
+              test_ostree_sysroot_boot_automount, teardown);
   /* TODO: More */
 
   return g_test_run ();