Added disable_symlinks directive. To completely disable symlinks (disable_symlinks on) we use openat(O_NOFOLLOW) for each path component to avoid races. To allow symlinks with the same owner (disable_symlinks if_not_owner), use openat() (followed by fstat()) and fstatat(AT_SYMLINK_NOFOLLOW), and then compare uids between fstat() and fstatat(). As there is a race between openat() and fstatat() we don't know if openat() in fact opened symlink or not. Therefore, we have to compare uids even if fstatat() reports the opened component isn't a symlink (as we don't know whether it was symlink during openat() or not). Default value is off, i.e. symlinks are allowed.

--- a/src/http/ngx_http_core_module.h
+++ b/src/http/ngx_http_core_module.h
@@ -404,6 +404,10 @@ struct ngx_http_core_loc_conf_s {
 #endif
 #endif
 
+#if (NGX_HAVE_OPENAT)
+    ngx_uint_t    disable_symlinks;        /* disable_symlinks */
+#endif
+
     ngx_array_t  *error_pages;             /* error_page */
     ngx_http_try_file_t    *try_files;     /* try_files */