Commit 9060dd2c authored Nov 26, 2016 by Eric Sandeen Committed by Theodore Ts'o Nov 26, 2016

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 <shuwang@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>

parent 4f5a763c

fs/ext4/super.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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

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