core: Validate that xattr names aren't empty

In the ostree-ext codebase the test fixture was generating xattrs
without the trailing NUL byte.  This caused confusing errors
later.  Change the dirmeta validator to catch this.

The way GVariant represents bytestrings, the trailing NUL is there
on wire/disk so it can be there in memory too, but `g_variant_get_bytestring()`
will just return an empty `""` string if actually the value
has a missing NUL.

Signed-off-by: Colin Walters <walters@verbum.org>

src/libostree/ostree-core-private.h

@@ -90,6 +90,7 @@ void _ostree_gfileinfo_to_stbuf (GFileInfo *file_info, struct stat *out_stbuf);
 gboolean _ostree_gfileinfo_equal (GFileInfo *a, GFileInfo *b);
 gboolean _ostree_stbuf_equal (struct stat *stbuf_a, struct stat *stbuf_b);
 GFileInfo *_ostree_mode_uidgid_to_gfileinfo (mode_t mode, uid_t uid, gid_t gid);
+gboolean _ostree_validate_structureof_xattrs (GVariant *xattrs, GError **error);
 
 static inline void
 _ostree_checksum_inplace_from_bytes_v (GVariant *csum_v, char *buf)

src/libostree/ostree-core.c

@@ -2277,6 +2277,27 @@ ostree_validate_structureof_file_mode (guint32 mode, GError **error)
   return TRUE;
 }
 
+/* Currently ostree imposes no restrictions on xattrs on its own;
+ * they can e.g. be arbitrariliy sized or in number.
+ * However, we do validate the key is non-empty, as that is known
+ * to always fail.
+ */
+gboolean
+_ostree_validate_structureof_xattrs (GVariant *xattrs, GError **error)
+{
+  const guint n = g_variant_n_children (xattrs);
+  for (guint i = 0; i < n; i++)
+    {
+      const guint8 *name;
+      g_autoptr (GVariant) value = NULL;
+      g_variant_get_child (xattrs, i, "(^&ay@ay)", &name, &value);
+      if (!*name)
+        return glnx_throw (error, "Invalid xattr name (empty or missing NUL) index=%d", i);
+      i++;
+    }
+  return TRUE;
+}
+
 /**
  * ostree_validate_structureof_dirmeta:
  * @dirmeta: A dirmeta object, %OSTREE_OBJECT_TYPE_DIR_META
@@ -2303,6 +2324,10 @@ ostree_validate_structureof_dirmeta (GVariant *dirmeta, GError **error)
   if (!validate_stat_mode_perms (mode, error))
     return FALSE;
 
+  g_autoptr (GVariant) xattrs = g_variant_get_child_value (dirmeta, 3);
+  if (!_ostree_validate_structureof_xattrs (xattrs, error))
+    return FALSE;
+
   return TRUE;
 }
 

src/libostree/ostree-repo-checkout.c

@@ -1123,7 +1123,7 @@ checkout_tree_at_recurse (OstreeRepo *self, OstreeRepoCheckoutAtOptions *options
   if (!did_exist && xattrs)
     {
       if (!glnx_fd_set_all_xattrs (destination_dfd, xattrs, cancellable, error))
-        return FALSE;
+        return glnx_prefix_error (error, "Processing dirmeta %s", dirmeta_checksum);
     }
 
   /* Process files in this subdir */

src/libostree/ostree-repo-commit.c

@@ -139,6 +139,8 @@ gboolean
 _ostree_write_bareuser_metadata (int fd, guint32 uid, guint32 gid, guint32 mode, GVariant *xattrs,
                                  GError **error)
 {
+  if (xattrs != NULL && !_ostree_validate_structureof_xattrs (xattrs, error))
+    return FALSE;
   g_autoptr (GVariant) filemeta = create_file_metadata (uid, gid, mode, xattrs);
 
   if (TEMP_FAILURE_RETRY (fsetxattr (fd, "user.ostreemeta", (char *)g_variant_get_data (filemeta),

tests/test-basic-c.c

@@ -513,6 +513,23 @@ test_read_xattrs (void)
   }
 }
 
+static void
+test_dirmeta_xattrs (void)
+{
+  g_autoptr (GError) local_error = NULL;
+  GError **error = &local_error;
+  const guint32 uidgid = GUINT32_TO_BE (42);
+  const guint32 mode = GUINT32_TO_BE (S_IFDIR | S_IRWXU);
+  g_autoptr (GVariantBuilder) xattr_builder = g_variant_builder_new (G_VARIANT_TYPE ("a(ayay)"));
+  const char *data = "data";
+  g_variant_builder_add (xattr_builder, "(@ay@ay)", g_variant_new_bytestring (""),
+                         g_variant_new_bytestring (data));
+  g_autoptr (GVariant) dirmeta = g_variant_new ("(uuu@a(ayay))", uidgid, uidgid, mode,
+                                                g_variant_builder_end (xattr_builder));
+  g_assert (!ostree_validate_structureof_dirmeta (dirmeta, error));
+  g_assert_error (local_error, G_IO_ERROR, G_IO_ERROR_FAILED);
+}
+
 int
 main (int argc, char **argv)
 {
@@ -533,6 +550,7 @@ main (int argc, char **argv)
   g_test_add_func ("/remotename", test_validate_remotename);
   g_test_add_func ("/big-metadata", test_big_metadata);
   g_test_add_func ("/read-xattrs", test_read_xattrs);
+  g_test_add_func ("/dirmeta-xattrs", test_dirmeta_xattrs);
 
   return g_test_run ();
 out: