The commit 031bb5a5d0d950253b68138b498dc93be69a64cb directly addresses the vulnerability. The patch modifies the protect_dir function in modules/pam_namespace/pam_namespace.c. The core of the vulnerability lies in how protect_dir used openat. Before the patch, openat was called with flags = O_RDONLY. If the path pointed to a FIFO, openat would block. The patch changes flags to O_RDONLY | O_DIRECTORY, which causes openat to fail if the path is not a directory, thus preventing the blocking behavior and the DoS. The removed code block, which manually checked if the opened path was a directory using fstat and S_ISDIR, further confirms that protect_dir was the function handling the problematic logic.