From: Eric Sandeen Subject: [PATCH] ext4: fix mmp use after free during unmount Date: Thu, 20 Oct 2016 13:19:39 -0500 Message-ID: <0b8909ed-ae65-1a89-263c-12aff513377a@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: shuwang@redhat.com To: "linux-ext4@vger.kernel.org" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:38570 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752101AbcJTSTl (ORCPT ); Thu, 20 Oct 2016 14:19:41 -0400 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CAF1719D22F for ; Thu, 20 Oct 2016 18:19:40 +0000 (UTC) Sender: linux-ext4-owner@vger.kernel.org List-ID: In ext4_put_super, we call brelse on the buffer head containing the ext4 superblock, but then try to use it when we stop the mmp thread, because when the thread shuts down it does: write_mmp_block ext4_mmp_csum_set ext4_has_metadata_csum WARN_ON_ONCE(ext4_has_feature_metadata_csum(sb)...) which reaches into sb->s_fs_info->s_es->s_feature_ro_compat, which lives in the superblock buffer s_sbh which we just released. Fix this by moving the brelse down to a point where we are no longer using it. Reported-by: Wang Shu Signed-off-by: Eric Sandeen --- Note: found by inspection after a bug report via KASAN, compile-tested only. diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 6db81fb..f273212 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -862,7 +862,6 @@ static void ext4_put_super(struct super_block *sb) percpu_counter_destroy(&sbi->s_dirs_counter); percpu_counter_destroy(&sbi->s_dirtyclusters_counter); percpu_free_rwsem(&sbi->s_journal_flag_rwsem); - brelse(sbi->s_sbh); #ifdef CONFIG_QUOTA for (i = 0; i < EXT4_MAXQUOTAS; i++) kfree(sbi->s_qf_names[i]); @@ -894,6 +893,9 @@ static void ext4_put_super(struct super_block *sb) } if (sbi->s_mmp_tsk) kthread_stop(sbi->s_mmp_tsk); + + /* Don't let this go until everything is done with the ext4 super */ + brelse(sbi->s_sbh); sb->s_fs_info = NULL; /* * Now that we are completely done shutting down the