From 9060dd2c5036b12132f9b97e3486ca6422d5bdfc Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Sat, 26 Nov 2016 14:24:51 -0500 Subject: [PATCH] ext4: fix mmp use after free during unmount 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 Signed-off-by: Theodore Ts'o Reviewed-by: Andreas Dilger --- fs/ext4/super.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index bb3a8ed..a526956 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -863,7 +863,6 @@ 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]); @@ -895,6 +894,7 @@ static void ext4_put_super(struct super_block *sb) } if (sbi->s_mmp_tsk) kthread_stop(sbi->s_mmp_tsk); + brelse(sbi->s_sbh); sb->s_fs_info = NULL; /* * Now that we are completely done shutting down the -- 2.7.4