linux-ext4 - Re: [Ext4 Secure Delete 5/7v4] ext4: Secure Delete: Secure delete directory entry

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Date:	Fri, 7 Oct 2011 10:22:26 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Allison Henderson <achender@...ux.vnet.ibm.com>
Cc:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [Ext4 Secure Delete 5/7v4] ext4: Secure Delete: Secure delete
	directory entry

On Fri, Oct 07, 2011 at 12:11:03AM -0700, Allison Henderson wrote:
> This patch zeros or randomizes a files directory entry when a file
<snip>
> @@ -1669,7 +1672,38 @@ static int ext4_delete_entry(handle_t *handle,
>  				de->inode = 0;
>  			dir->i_version++;
>  			BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
> -			err = ext4_handle_dirty_metadata(handle, dir, bh);
> +
> +			/*
> +			 * If the secure remove flag is on, zero
> +			 * or randomize the entry and write it out
> +			 * to the disk
> +			 */
> +			if (flags & EXT4_DEL_ENTRY_ZERO) {
> +				memset(de->name, 0x00, de->name_len);
> +				de->file_type = 0;
> +			} else if (flags & EXT4_DEL_ENTRY_RAND) {
> +				get_random_bytes(de->name, de->name_len);
> +				get_random_bytes(&(de->file_type),
> +					sizeof(de->file_type));

Seeing as name_len and file_type precede name, you could probably reduce this
to one call that zaps all three.  Same for the zero-out case.

Also you might want to make both of these name-erasing calls zap the space
between the end of the name and the end of the record, just in case there's old
filename component still lurking in that space.  (Yes, paranoia...)

> +			}
> +
> +			if (flags & EXT4_DEL_ENTRY_ZERO ||
> +				flags & EXT4_DEL_ENTRY_RAND) {
> +
> +				set_buffer_dirty(bh);
> +				sync_dirty_buffer(bh);
> +				if (buffer_req(bh) && !buffer_uptodate(bh)) {
> +					es->s_last_error_block =
> +						cpu_to_le64(bh->b_blocknr);
> +					ext4_error_inode(dir, __func__,
> +					   __LINE__, bh->b_blocknr,
> +					   "IO error syncing itable block");

itable?

--D
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