ext4: fix dir corruption when ext4_dx_add_entry() fails

Following process may lead to fs corruption:
1. ext4_create(dir/foo)
 ext4_add_nondir
  ext4_add_entry
   ext4_dx_add_entry
     a. add_dirent_to_buf
      ext4_mark_inode_dirty
      ext4_handle_dirty_metadata   // dir inode bh is recorded into journal
     b. ext4_append    // dx_get_count(entries) == dx_get_limit(entries)
       ext4_bread(EXT4_GET_BLOCKS_CREATE)
        ext4_getblk
         ext4_map_blocks
          ext4_ext_map_blocks
            ext4_mb_new_blocks
             dquot_alloc_block
              dquot_alloc_space_nodirty
               inode_add_bytes    // update dir's i_blocks
            ext4_ext_insert_extent
	     ext4_ext_dirty  // record extent bh into journal
              ext4_handle_dirty_metadata(bh)
	      // record new block into journal
       inode->i_size += inode->i_sb->s_blocksize   // new size(in mem)
     c. ext4_handle_dirty_dx_node(bh2)
	// record dir's new block(dx_node) into journal
     d. ext4_handle_dirty_dx_node((frame - 1)->bh)
     e. ext4_handle_dirty_dx_node(frame->bh)
     f. do_split    // ret err!
     g. add_dirent_to_buf
	 ext4_mark_inode_dirty(dir)  // update raw_inode on disk(skipped)
2. fsck -a /dev/sdb
 drop last block(dx_node) which beyonds dir's i_size.
  /dev/sdb: recovering journal
  /dev/sdb contains a file system with errors, check forced.
  /dev/sdb: Inode 12, end of extent exceeds allowed value
	(logical block 128, physical block 3938, len 1)
3. fsck -fn /dev/sdb
 dx_node->entry[i].blk > dir->i_size
  Pass 2: Checking directory structure
  Problem in HTREE directory inode 12 (/dir): bad block number 128.
  Clear HTree index? no
  Problem in HTREE directory inode 12: block #3 has invalid depth (2)
  Problem in HTREE directory inode 12: block #3 has bad max hash
  Problem in HTREE directory inode 12: block #3 not referenced

Fix it by marking inode dirty directly inside ext4_append().
Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216466
Cc: [email protected]
Signed-off-by: Zhihao Cheng <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

fs/ext4/namei.c

@@ -85,15 +85,20 @@ static struct buffer_head *ext4_append(handle_t *handle,
 		return bh;
 	inode->i_size += inode->i_sb->s_blocksize;
 	EXT4_I(inode)->i_disksize = inode->i_size;
+	err = ext4_mark_inode_dirty(handle, inode);
+	if (err)
+		goto out;
 	BUFFER_TRACE(bh, "get_write_access");
 	err = ext4_journal_get_write_access(handle, inode->i_sb, bh,
 					    EXT4_JTR_NONE);
-	if (err) {
-		brelse(bh);
-		ext4_std_error(inode->i_sb, err);
-		return ERR_PTR(err);
-	}
+	if (err)
+		goto out;
 	return bh;
+
+out:
+	brelse(bh);
+	ext4_std_error(inode->i_sb, err);
+	return ERR_PTR(err);
 }
 
 static int ext4_dx_csum_verify(struct inode *inode,