core: Ignore subdirectories of /usr/lib/modules without a kernel

There's a valid use case of installing a 3rd party RPM which has
pre-built kmods for *multiple* kernel versions.  What we care about
here is that there aren't actually multiple kernel binaries aka
`vmlinuz`.

Closes: #3965

src/libpriv/rpmostree-kernel.cxx

@@ -105,13 +105,13 @@ find_kernel_and_initramfs_in_bootdir (int rootfs_dfd, const char *bootdir, char
   return TRUE;
 }
 
-/* Given a directory @subpath, find the first child that is a directory,
- * returning it in @out_subdir.  If there are multiple directories,
+/* Given a directory @subpath, find the first child that is a directory
+ * and contains a `vmlinuz` file, returning it in @out_subdir.  If there are multiple directories,
  * return an error.
  */
 static gboolean
-find_ensure_one_subdirectory (int rootfs_dfd, const char *subpath, char **out_subdir,
-                              GCancellable *cancellable, GError **error)
+find_dir_with_vmlinuz (int rootfs_dfd, const char *subpath, char **out_subdir,
+                       GCancellable *cancellable, GError **error)
 {
   g_autofree char *ret_subdir = NULL;
   g_auto (GLnxDirFdIterator) dfd_iter = {
@@ -132,11 +132,18 @@ find_ensure_one_subdirectory (int rootfs_dfd, const char *subpath, char **out_su
 
       if (dent->d_type != DT_DIR)
         continue;
+      // Ignore directories without vmlinuz
+      struct stat stbuf;
+      g_autofree char *vmlinuz_path = g_strdup_printf ("%s/vmlinuz", dent->d_name);
+      if (!glnx_fstatat_allow_noent (dfd_iter.fd, vmlinuz_path, &stbuf, AT_SYMLINK_NOFOLLOW, error))
+        return FALSE;
+      if (errno == ENOENT)
+        continue;
 
       if (ret_subdir)
         {
           g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
-                       "Multiple subdirectories found in: %s: %s %s", subpath,
+                       "Multiple kernels (vmlinuz) found in: %s: %s %s", subpath,
                        glnx_basename (ret_subdir), dent->d_name);
           return FALSE;
         }
@@ -179,8 +186,7 @@ gboolean
 rpmostree_kernel_remove (int rootfs_dfd, GCancellable *cancellable, GError **error)
 {
   g_autofree char *modversion_dir = NULL;
-  if (!find_ensure_one_subdirectory (rootfs_dfd, "usr/lib/modules", &modversion_dir, cancellable,
-                                     error))
+  if (!find_dir_with_vmlinuz (rootfs_dfd, "usr/lib/modules", &modversion_dir, cancellable, error))
     return FALSE;
   if (modversion_dir)
     {
@@ -231,8 +237,7 @@ rpmostree_find_kernel (int rootfs_dfd, GCancellable *cancellable, GError **error
 {
   /* Fetch the kver from /usr/lib/modules */
   g_autofree char *modversion_dir = NULL;
-  if (!find_ensure_one_subdirectory (rootfs_dfd, "usr/lib/modules", &modversion_dir, cancellable,
-                                     error))
+  if (!find_dir_with_vmlinuz (rootfs_dfd, "usr/lib/modules", &modversion_dir, cancellable, error))
     return NULL;
 
   if (!modversion_dir)

tests/compose/test-misc-tweaks.sh

@@ -13,6 +13,12 @@ build_rpm foobar-rec
 build_rpm quuz
 build_rpm corge version 1.0
 build_rpm corge version 2.0
+build_rpm thirdpartymodules version 2.3 \
+  files "/usr/lib/modules/4.7.8-10.x86_64/foo.ko
+         /usr/lib/modules/4.9.3-2.x86_64/foo.ko
+         /usr/lib/modules/5.8.1-11.x86_64/foo.ko
+         " \
+  install "for v in 4.7.8-10.x86_64 4.9.3-2.x86_64 5.8.1-11.x86_64; do d=%{buildroot}/usr/lib/modules/\$v; mkdir -p \$d && echo kmod\$v > \$d/foo.ko; done"
 # test `remove-from-packages` (files shared with other pkgs should not be removed)
 build_rpm barbar \
           files "/etc/sharedfile
@@ -26,7 +32,7 @@ build_rpm barbaz \
 echo gpgcheck=0 >> yumrepo.repo
 ln "$PWD/yumrepo.repo" config/yumrepo.repo
 # the top-level manifest doesn't have any packages, so just set it
-treefile_append "packages" $'["\'foobar >= 0.5\' quuz \'corge < 2.0\' barbar barbaz"]'
+treefile_append "packages" $'["\'foobar >= 0.5\' quuz \'corge < 2.0\' barbar barbaz thirdpartymodules"]'
 
 # With docs and recommends, also test multi includes
 cat > config/documentation.yaml <<'EOF'

tests/kolainst/destructive/container-image

@@ -159,6 +159,9 @@ ADD baz-2.0-1.x86_64.rpm /run/rpm-ostree/staged-rpms/${baz_chksum}.rpm
 RUN rpm-ostree ex rebuild
 RUN echo some config file > /etc/someconfig.conf
 RUN echo somedata > /usr/share/somenewdata
+# Verify we're ignoring subdirectories that don't contain vmlinuz https://github.com/coreos/rpm-ostree/issues/3965
+RUN mkdir -p /usr/lib/modules/blah && touch /usr/lib/modules/blah/foo
+RUN rpm-ostree cleanup -m
 EOF
     # Older podman found in RHEL8 blows up without /etc/resolv.conf
     # which happens in our qemu path.