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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>
This commit is contained in:
Eric Sandeen 2016-11-26 14:24:51 -05:00 committed by Theodore Ts'o
parent 4f5a763c9a
commit 9060dd2c50
1 changed files with 1 additions and 1 deletions
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2
fs/ext4/super.c
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@ -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