From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Sahitya Tummala , Theodore Tso , Amit Pundir Subject: [PATCH 4.4 08/50] jbd2: fix use after free in kjournald2() Date: Fri, 27 Apr 2018 15:58:10 +0200 Message-Id: <20180427135656.135152291@linuxfoundation.org> In-Reply-To: <20180427135655.623669681@linuxfoundation.org> References: <20180427135655.623669681@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sahitya Tummala commit dbfcef6b0f4012c57bc0b6e0e660d5ed12a5eaed upstream. Below is the synchronization issue between unmount and kjournald2 contexts, which results into use after free issue in kjournald2(). Fix this issue by using journal->j_state_lock to synchronize the wait_event() done in journal_kill_thread() and the wake_up() done in kjournald2(). TASK 1: umount cmd: |--jbd2_journal_destroy() { |--journal_kill_thread() { write_lock(&journal->j_state_lock); journal->j_flags |= JBD2_UNMOUNT; ... write_unlock(&journal->j_state_lock); wake_up(&journal->j_wait_commit); TASK 2 wakes up here: kjournald2() { ... checks JBD2_UNMOUNT flag and calls goto end-loop; ... end_loop: write_unlock(&journal->j_state_lock); journal->j_task = NULL; --> If this thread gets pre-empted here, then TASK 1 wait_event will exit even before this thread is completely done. wait_event(journal->j_wait_done_commit, journal->j_task == NULL); ... write_lock(&journal->j_state_lock); write_unlock(&journal->j_state_lock); } |--kfree(journal); } } wake_up(&journal->j_wait_done_commit); --> this step now results into use after free issue. } Signed-off-by: Sahitya Tummala Signed-off-by: Theodore Ts'o Cc: Amit Pundir Signed-off-by: Greg Kroah-Hartman --- fs/jbd2/journal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -275,11 +275,11 @@ loop: goto loop; end_loop: - write_unlock(&journal->j_state_lock); del_timer_sync(&journal->j_commit_timer); journal->j_task = NULL; wake_up(&journal->j_wait_done_commit); jbd_debug(1, "Journal thread exiting.\n"); + write_unlock(&journal->j_state_lock); return 0; }