linux-kernel - Re: [PATCH] Support for secure erase functionality

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Date:   Fri, 22 Sep 2017 11:54:36 +0200
From:   Máté Horváth <horvatmate@...il.com>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     Philipp Guendisch <philipp.guendisch@....de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, damien.lemoal@....com,
        axboe@...nel.dk, viro@...iv.linux.org.uk,
        bart.vanassche@...disk.com, martin.petersen@...cle.com,
        hare@...e.de, osandov@...com, dan.j.williams@...el.com,
        ming.lei@...hat.com, linux-kernel@...cs.fau.de
Subject: Re: [PATCH] Support for secure erase functionality

Dear Johannes Thumshirn,

> How can this work with CoW filesystems?

Because we are a layer below filesystems, that depends on the actual
implementation.
If the discards are issued to the right sectors on the drive, we write
into those sectors.


>> Built against torvalds/linux
>
> This should go below the '---' so git am doesn't write it into the changelog.

Thanks for the hint, we messed that up.


> Which filesystems commonly used in production are left afterwards?

The list of filesystems you see in the code are the working ones
(except btrfs, that apparently
doesn't mount a block device, so it doesn't run into our code - we
have to look into that).
Which other filesystems do you miss?

> I'm sorry, but while I get that this sounds like a nice feature for a paper or
> reasearch project, I don't see why it should be used on production systems at
> all.

This feature could be used, if you can't afford to use a full disk
encryption, but still want to
erase sensitive data on the fly. As you probably read in the other
mails, this solution is
not forensic-proof, but with a normal data recovery tool, you
shouldn't be able to recover
more than the file name

Best regards,
Máté Horváth


2017-09-14 10:17 GMT+02:00 Johannes Thumshirn <jthumshirn@...e.de>:
> On Wed, Sep 13, 2017 at 05:37:53PM +0200, Philipp Guendisch wrote:
>> This patch adds a software based secure erase option to improve data
>> confidentiality. The CONFIG_BLK_DEV_SECURE_ERASE option enables a mount
>> flag called 'sw_secure_erase'. When you mount a volume with this flag,
>> every discard call is prepended by an explicit write command to overwrite
>> the data before it is discarded. A volume without a discard compatibility
>> can be used as well but the discard calls will be enabled for this device
>> and suppressed after the write call is made.
>
> How can this work with CoW filesystems?
>
>>
>> Built against torvalds/linux
>
> This should go below the '---' so git am doesn't write it into the changelog.
>
>
> [...]
>
>> +     if (strcmp(fs_type->name, "ext4") != 0 &&
>> +         strcmp(fs_type->name, "btrfs") != 0 &&
>> +         strcmp(fs_type->name, "gfs2") != 0 &&
>> +         strcmp(fs_type->name, "gfs2meta") != 0 &&
>> +         strcmp(fs_type->name, "xfs") != 0 &&
>> +         strcmp(fs_type->name, "jfs") != 0) {
>> +             pr_warn("fs: The mounted %s filesystem on drive %s does not generate discards, secure erase won't work",
>> +                             fs_type->name, dev_name);
>> +     }
>> +skip:
>> +#endif
>
> Which filesystems commonly used in production are left afterwards?
>
> I'm sorry, but while I get that this sounds like a nice feature for a paper or
> reasearch project, I don't see why it should be used on production systems at
> all.
>
> Byte,
>         Johannes
> --
> Johannes Thumshirn                                          Storage
> jthumshirn@...e.de                                +49 911 74053 689
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