Message-ID: <4E8F9412.8040607@linux.vnet.ibm.com>
Date:	Fri, 07 Oct 2011 17:06:42 -0700
From:	Allison Henderson <achender@...ux.vnet.ibm.com>
To:	djwong@...ibm.com
CC:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [Ext4 Secure Delete 7/7v4] ext4/jbd2: Secure Delete: Secure delete
 journal blocks

On 10/07/2011 01:58 PM, Darrick J. Wong wrote:
> On Fri, Oct 07, 2011 at 12:55:30PM -0700, Allison Henderson wrote:
>> On 10/07/2011 11:35 AM, Darrick J. Wong wrote:
>>> On Fri, Oct 07, 2011 at 12:11:05AM -0700, Allison Henderson wrote:
>>>> This patch modifies both ext4 and jbd2 such that the journal
>>>> blocks which may contain file data, are securely deleted
>>>> after the files data blocks are deleted.
>>>>
>>>> Because old journal blocks may contain file data, we need
>>>> a way to find those blocks again when it comes time to secure
>>>> delete the file.  This patch adds a new list to the journal
>>>> structure to keep track of which vfs blocks the journal blocks
>>>> contain.
>>>>
>>>> After a truncate or a punch hole operation has completed, a
>>>> new function ext4_secure_delete_jblks is called that flushes
>>>> the journal, and then searches the list for any journal blocks
>>>> that were used to journal the blocks that were just removed.
>>>> The found journal blocks are then secure deleted.
>>>>
>>>> Signed-off-by: Allison Henderson<achender@...ux.vnet.ibm.com>
>>>> ---
>>>> :100644 100644 0cba63b... fdf73b5... M	fs/ext4/ext4.h
>>>> :100644 100644 984fac2... 81df943... M	fs/ext4/extents.c
>>>> :100644 100644 bd1facd... 083c516... M	fs/ext4/inode.c
>>>> :100644 100644 eef6979... 2734e7b... M	fs/jbd2/commit.c
>>>> :100644 100644 f24df13... 6dd8af7... M	fs/jbd2/journal.c
>>>> :100644 100644 38f307b... 8b84b43... M	include/linux/jbd2.h
>>>>    fs/ext4/ext4.h       |    3 +
>>>>    fs/ext4/extents.c    |   12 +++++
>>>>    fs/ext4/inode.c      |  110 +++++++++++++++++++++++++++++++++++++++++++++++++
>>>>    fs/jbd2/commit.c     |    6 +++
>>>>    fs/jbd2/journal.c    |  112 ++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>    include/linux/jbd2.h |   21 +++++++++
>>>>    6 files changed, 264 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>>>> index 0cba63b..fdf73b5 100644
>>>> --- a/fs/ext4/ext4.h
>>>> +++ b/fs/ext4/ext4.h
>>>> @@ -2230,6 +2230,9 @@ extern int ext4_secure_delete_lblks(struct inode *inode,
>>>>    			ext4_lblk_t first_block, unsigned long count);
>>>>    extern int ext4_secure_delete_pblks(struct inode *inode,
>>>>    			ext4_fsblk_t block, unsigned long count);
>>>> +extern int ext4_secure_delete_jblks(struct inode *inode,
>>>> +				ext4_lblk_t first_block, unsigned long count);
>>>> +
>>>>
>>>>    /* move_extent.c */
>>>>    extern int ext4_move_extents(struct file *o_filp, struct file *d_filp,
>>>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>>>> index 984fac2..81df943 100644
>>>> --- a/fs/ext4/extents.c
>>>> +++ b/fs/ext4/extents.c
>>>> @@ -4159,6 +4159,7 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
>>>>    	struct super_block *sb = inode->i_sb;
>>>>    	struct ext4_ext_cache cache_ex;
>>>>    	ext4_lblk_t first_block, last_block, num_blocks, iblock, max_blocks;
>>>> +	ext4_lblk_t first_secrm_blk, last_secrm_blk, secrm_blk_count;
>>>>    	struct address_space *mapping = inode->i_mapping;
>>>>    	struct ext4_map_blocks map;
>>>>    	handle_t *handle;
>>>> @@ -4317,6 +4318,17 @@ out:
>>>>    	inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
>>>>    	ext4_mark_inode_dirty(handle, inode);
>>>>    	ext4_journal_stop(handle);
>>>> +
>>>> +	if (!err&&   EXT4_I(inode)->i_flags&   EXT4_SECRM_FL) {
>>>> +		first_secrm_blk = offset>>   EXT4_BLOCK_SIZE_BITS(sb);
>>>> +		last_secrm_blk = (offset + length + sb->s_blocksize - 1)>>
>>>> +			EXT4_BLOCK_SIZE_BITS(sb);
>>>> +		secrm_blk_count = last_secrm_blk - first_secrm_blk;
>>>> +
>>>> +		err = ext4_secure_delete_jblks(inode,
>>>> +		   first_secrm_blk, secrm_blk_count);
>>>> +	}
>>>> +
>>>>    	return err;
>>>>    }
>>>>    int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>>>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>>>> index bd1facd..083c516 100644
>>>> --- a/fs/ext4/inode.c
>>>> +++ b/fs/ext4/inode.c
>>>> @@ -909,6 +909,110 @@ int ext4_secure_delete_lblks(struct inode *inode, ext4_lblk_t first_block,
>>>>    	return err;
>>>>    }
>>>>
>>>> +/*
>>>> + * ext4_secure_delete_jblks()
>>>> + *
>>>> + * Secure deletes the journal blocks that contain
>>>> + * the specified logical blocks
>>>> + *
>>>> + * @inode: The files inode
>>>> + * @first_block: Starting logical block
>>>> + * @count: The number of blocks to secure delete
>>>> + *         from the journal
>>>> + *
>>>> + * Returns 0 on sucess or negative on error
>>>> + */
>>>> +int ext4_secure_delete_jblks(struct inode *inode,
>>>> +				ext4_lblk_t first_block, unsigned long count){
>>>> +
>>>> +	unsigned long long jbd2_pblk_start = 0;
>>>> +	unsigned long long jbd2_pblk_count = 0;
>>>> +	ext4_lblk_t last_block = 0;
>>>> +	struct list_head *tmp = NULL;
>>>> +	struct list_head *cur = NULL;
>>>> +	struct jbd2_blk_pair *b_pair = NULL;
>>>> +	int err = 0;
>>>> +	journal_t *journal = EXT4_JOURNAL(inode);
>>>> +
>>>> +	/* Do not allow last_block to wrap */
>>>> +	last_block = first_block + count;
>>>> +	if (last_block<   first_block)
>>>> +		last_block = EXT_MAX_BLOCKS;
>>>> +
>>>> +	/*
>>>> +	 * Force the journal to finnish up any pending transactions
>>>> +	 * before we start secure deleteing journal blocks
>>>> +	 */
>>>> +	err = ext4_force_commit((inode)->i_sb);
>>>> +	if (err)
>>>> +		return err;
>>>> +
>>>> +	spin_lock(&journal->j_pair_lock);
>>>> +
>>>> +	/* Loop over the journals blocks looking for our logical blocks */
>>>> +	list_for_each_safe(cur, tmp,&journal->blk_pairs) {
>>>> +		b_pair = list_entry(cur, struct jbd2_blk_pair, list);
>>>
>>> Um.... I don't think ext4 should be accessing journal internals.  At a bare
>>> minimum the stuff that mucks around with jbd2 ought to be in fs/jbd2 and
>>> the ext4 parts stuffed in a wrapper in ext4_jbd2.[ch], since ocfs2 also uses
>>> jbd2.
>>
>> Ok, I can move the looping the jbd2 and set up a call back for doing the
>> actual secure deleting
>>
>>>
>>> I'm also wondering -- this logical<->   journal block mapping doesn't seem to be
>>> committed to disk anywhere.  What happens if jbd2 crashes before we get to
>>> zeroing journal blocks?  Specifically, would the journal recovery code know
>>> that a given journal block also needs secure deletion?
>>>
>>> Here's a counterproposal: What if ext4 told jbd2 which blocks need to be
>>> securely deleted while ext4 is creating the transactions?  jbd2 could then set
>>> a JBD2_FLAG_SECURE_DELETE flag in journal_block_tag_t.t_flags (the descriptor
>>> block), which would tell the recovery and commit code that the associated
>>> journal block needs secure deletion when processing is complete.  I _think_ you
>>> could just extend the functions called by ext4_jbd2.c to take a flags
>>> parameter.  Does this sound better?  Or even sane? :)
>>>
>>> (Not sure if ocfs2 cares about secure delete at all.)
>>>
>>> --D
>>>
>>
>> Well actually I had initially started out with something that tried to
>> do the secure delete when the transactions had completed, but it didnt
>> work out because most of the time the transactions had already long
>> since completed before the secure delete flag even gets turned on. And
>
> Ahh, I see, you're concerned that:
>
> $ touch /mnt/afile		# A
> $ sync
> $ chattr +s /mnt/afile
> $ rm -rf /mnt/afile
>
> ...doesn't secure delete the journal blocks associated with the inode creation
> in step A, because one cannot create files with the secure deletion flag set.
> I could think of a few ways out of this...
>
> 0) Simply accept that there's no way to create files with "secure delete" set;
> therefore, the inode creation and dir entry creation will always be hanging out
> in the journal.  This requires users to notice this little detail and get the
> following details correct: if filenames are important, then they'll have to
> create the file with a bogus name, chattr +s, create a hard link with the real
> name, and then unlink the first bogus name. (ha ha....)
>
> 1) When creating a file, lie to the journal by always telling it to securely
> delete the blocks associated with the file create.  If the user really wants
> secure deletion, the next step after creating the file ought to be setting the
> +s flag.  This has the advantage that even the generic "new inode" contents are
> also protected by secure deletion, which #0 doesn't provide.  However, we'd
> take a speed hit for a feature that isn't necessarily the common case.
>
> 2) Teach the journal to keep track of the pblocks and go back and retroactively
> delete older copies, sort of like what your current patch does.
>
> As a side note, we could probably discard journal blocks when the transaction
> finishes committing and flushing.
>

Alrighty, you've given me a few more ideas to play with.  I think I may 
go back and do a little more prototyping and see what I can come up 
with.  Thx for the thorough review!!

Allison Henderson

>> then when we turn on the flag and start deleting, I have to get those
>> old journal blocks back.  So I think the new idea might have the same
>> problem.  But I think your right about needing to somehow commit it to
>> the disk, otherwise those old journal blocks will still be there after a
>> crash.
>
>
>
> --D

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