[wp-trac] [WordPress Trac] #51962: Race condition in wp_get_custom_css_post() would clear the custom CSS entry

[WordPress Trac]

#51962: Race condition in wp_get_custom_css_post() would clear the custom CSS entry
--------------------------+-----------------------------
 Reporter:  candrei       |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  General       |    Version:  5.5.3
 Severity:  normal        |   Keywords:
  Focuses:                |
--------------------------+-----------------------------
 Our production system was recently affected by a (what it looks to me)
 race condition in `wp_get_custom_css_post()`; for reference here's the
 code in question:
 {{{#!php

         if ( get_stylesheet() === $stylesheet ) {
                 $post_id = get_theme_mod( 'custom_css_post_id' );

                 if ( $post_id > 0 && get_post( $post_id ) ) {
                         $post = get_post( $post_id );
                 }

                 // `-1` indicates no post exists; no query necessary.
                 if ( ! $post && -1 !== $post_id ) {
                         $query = new WP_Query( $custom_css_query_vars );
                         $post  = $query->post;
                         /*
                          * Cache the lookup. See
 wp_update_custom_css_post().
                          * @todo This should get cleared if a custom_css
 post is added/removed.
                          */
                         set_theme_mod( 'custom_css_post_id', $post ?
 $post->ID : -1 );
                 }
         } else {

 }}}


 Our database went down after retrieving the `$post_id` from options.
 `get_post()` failed silently followed by `new WP_Query(
 $custom_css_query_vars );` that failed too while the DB was down.
 Eventually the DB became available and the `custom_css_post_id` setting
 was set to `-1`.

 As a result our website's styling was affected until we were able to
 restore the custom CSS stored in the `custom_css` post.

 I think better error handling within the `wp_get_custom_css_post()` could
 prevent such side effect from taking place.

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Ticket URL: <https://core.trac.wordpress.org/ticket/51962>
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