Re: [PATCH 1/2 v3] EXT4: Secure Delete: Zero out file data

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On Fri, Jul 1, 2011 at 12:22 AM, Allison Henderson
<achender@xxxxxxxxxxxxxxxxxx> wrote:
> The first patch adds a new flag, EXT4_FREE_BLOCKS_ZERO,
> to ext4_free_blocks. This flag causes causes blocks to be
> zerod before they are freed.  Files that have the EXT4_SECRM_FL
> attribute flag on will have their blocks zerod when
> they are released.  The EXT4_SECRM_FL attribute flag can
> be enabled useing chattr +s
>
> Signed-off-by: Allison Henderson <achender@xxxxxxxxxxxxxxxxxx>
> ---
> v1->v2
> Removed check for discard mount option and replaced with
> check for secure discard and discard_zeroes_data
>
> Added BLKDEV_DISCARD_SECURE to the sb_issue_discard call
>
> v2->v3
> Removed code for discard.  A seperate patch will
> be done to add that code in the block layer
>
> :100644 100644 1921392... 38a4d75... M  fs/ext4/ext4.h
> :100644 100644 f815cc8... cf178f3... M  fs/ext4/extents.c
> :100644 100644 62f86e7... 8fdae7d... M  fs/ext4/inode.c
> :100644 100644 6ed859d... 94872b2... M  fs/ext4/mballoc.c
> :100644 100644 c757adc... 1ff7532... M  fs/ext4/xattr.c
>  fs/ext4/ext4.h    |    1 +
>  fs/ext4/extents.c |    3 +++
>  fs/ext4/inode.c   |    3 +++
>  fs/ext4/mballoc.c |    8 ++++++++
>  fs/ext4/xattr.c   |   12 ++++++++----
>  5 files changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 1921392..38a4d75 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -526,6 +526,7 @@ struct ext4_new_group_data {
>  #define EXT4_FREE_BLOCKS_METADATA      0x0001
>  #define EXT4_FREE_BLOCKS_FORGET                0x0002
>  #define EXT4_FREE_BLOCKS_VALIDATED     0x0004
> +#define EXT4_FREE_BLOCKS_ZERO          0x0008
>
>  /*
>  * ioctl commands
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index f815cc8..cf178f3 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2231,6 +2231,9 @@ static int ext4_remove_blocks(handle_t *handle, struct inode *inode,
>
>        if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
>                flags |= EXT4_FREE_BLOCKS_METADATA;
> +
> +       if (EXT4_I(inode)->i_flags & EXT4_SECRM_FL)
> +               flags |= EXT4_FREE_BLOCKS_ZERO;
>  #ifdef EXTENTS_STATS
>        {
>                struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 62f86e7..8fdae7d 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4182,6 +4182,9 @@ static int ext4_clear_blocks(handle_t *handle, struct inode *inode,
>        for (p = first; p < last; p++)
>                *p = 0;
>
> +       if (EXT4_I(inode)->i_flags & EXT4_SECRM_FL)
> +               flags |= EXT4_FREE_BLOCKS_ZERO;
> +
>        ext4_free_blocks(handle, inode, NULL, block_to_free, count, flags);
>        return 0;
>  out_err:
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 6ed859d..94872b2 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4485,6 +4485,14 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
>        ext4_debug("freeing block %llu\n", block);
>        trace_ext4_free_blocks(inode, block, count, flags);
>
> +       if (flags & EXT4_FREE_BLOCKS_ZERO) {
> +               err = sb_issue_zeroout(inode->i_sb, block, count, GFP_NOFS);

But the delete of these blocks in not yet committed,
so after reboot, you can end up with a non-deleted but zeroed file data.
Is that acceptable? I should think not.

One way around this is a 2-phase unlink/truncate.
Phase 1: add to orphan list and register a callback on commit
Phase 2: issue zeroout and free the blocks

This won't work for punch hole, but then again, for punch hole
it's probably OK to end up with zeroed data, but non-deleted blocks.
Right?

Amir.

> +               if (err < 0)
> +                       goto error_return;
> +               else
> +                       err = 0;
> +       }
> +
>        if (flags & EXT4_FREE_BLOCKS_FORGET) {
>                struct buffer_head *tbh = bh;
>                int i;
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index c757adc..1ff7532 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -471,7 +471,7 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
>                         struct buffer_head *bh)
>  {
>        struct mb_cache_entry *ce = NULL;
> -       int error = 0;
> +       int free_blocks_flags, error = 0;
>
>        ce = mb_cache_entry_get(ext4_xattr_cache, bh->b_bdev, bh->b_blocknr);
>        error = ext4_journal_get_write_access(handle, bh);
> @@ -484,9 +484,13 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
>                if (ce)
>                        mb_cache_entry_free(ce);
>                get_bh(bh);
> -               ext4_free_blocks(handle, inode, bh, 0, 1,
> -                                EXT4_FREE_BLOCKS_METADATA |
> -                                EXT4_FREE_BLOCKS_FORGET);
> +               free_blocks_flags = EXT4_FREE_BLOCKS_METADATA |
> +                                       EXT4_FREE_BLOCKS_FORGET;
> +
> +               if (EXT4_I(inode)->i_flags & EXT4_SECRM_FL)
> +                       free_blocks_flags |= EXT4_FREE_BLOCKS_ZERO;
> +
> +               ext4_free_blocks(handle, inode, bh, 0, 1, free_blocks_flags);
>        } else {
>                le32_add_cpu(&BHDR(bh)->h_refcount, -1);
>                error = ext4_handle_dirty_metadata(handle, inode, bh);
> --
> 1.7.1
>
> --
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