[dm-crypt] Exhaustive key reading seems to silently stop on error

[dm-crypt] Exhaustive key reading seems to silently stop on error

[Nico R.]

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Hello!

Just a minute ago, I have subscribed to this list in order to let you
know about what I have found in the cryptsetup code and which seems to
be a bug to me.

In lib/utils.c (line 450f. in cryptsetup-1.0.7; line 490f. in current
SVN revision, r132, equal to r152), we see the following code:

if(read(fd, pass + i, 1) != 1 || (newline_stop && pass[i] == '\n'))
        break;

If I interpret that snipped (and its surroundings) correctly, the code
will read until EOF *or* until an error occurs.

If my interpretation is true, that code causes a problem: imagine a
hardware failure while reading the key the first two times (for
luksFormat/luksOpen). The read function returns -1 and sets errno to
EIO. cryptsetup continues with a truncated key, it seems. On a later
attempt to read the key (for luksOpen), the hardware failure is gone,
and the key can be read completely. cryptsetup will not be able to open
the encrypted partition anymore.

Please correct me if I got the code wrong … :-)

Thanks
-- 
Nico


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Re: [dm-crypt] Exhaustive key reading seems to silently stop on error

[Arno Wagner]

Hmm. This seems to indeed be a bug.

I gather there is no code later that distinguishes 
EOF and error and deals with the second possibility?

Arno


On Wed, Dec 09, 2009 at 11:25:53PM +0100, Nico R. wrote:
> Hello!
> 
> Just a minute ago, I have subscribed to this list in order to let you
> know about what I have found in the cryptsetup code and which seems to
> be a bug to me.
> 
> In lib/utils.c (line 450f. in cryptsetup-1.0.7; line 490f. in current
> SVN revision, r132, equal to r152), we see the following code:
> 
> if(read(fd, pass + i, 1) != 1 || (newline_stop && pass[i] == '\n'))
>         break;
> 
> If I interpret that snipped (and its surroundings) correctly, the code
> will read until EOF *or* until an error occurs.
> 
> If my interpretation is true, that code causes a problem: imagine a
> hardware failure while reading the key the first two times (for
> luksFormat/luksOpen). The read function returns -1 and sets errno to
> EIO. cryptsetup continues with a truncated key, it seems. On a later
> attempt to read the key (for luksOpen), the hardware failure is gone,
> and the key can be read completely. cryptsetup will not be able to open
> the encrypted partition anymore.
> 
> Please correct me if I got the code wrong?????? :-)
> 
> Thanks
> -- 
> Nico
> 



> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt


-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
----
Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans

If it's in the news, don't worry about it.  The very definition of 
"news" is "something that hardly ever happens." -- Bruce Schneier 

Re: [dm-crypt] Exhaustive key reading seems to silently stop on error

[Nico R.]

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Hi!

(De-TOFU-ized.)

> On Wed, Dec 09, 2009 at 11:25:53PM +0100, Nico R. wrote:
[…]
>> In lib/utils.c (line 450f. in cryptsetup-1.0.7; line 490f. in current
>> SVN revision, r132, equal to r152), we see the following code:
>>
>> if(read(fd, pass + i, 1) != 1 || (newline_stop && pass[i] == '\n'))
>>         break;
>>
>> If I interpret that snipped (and its surroundings) correctly, the code
>> will read until EOF *or* until an error occurs.
>>
>> If my interpretation is true, that code causes a problem:
[…]

Arno Wagner wrote:
> Hmm. This seems to indeed be a bug.
> 
> I gather there is no code later that distinguishes 
> EOF and error and deals with the second possibility?

As far as I can see, there is not. See
<URL:http://code.google.com/p/cryptsetup/source/browse/trunk/lib/utils.c?r=132#480>.
-- 
Nico


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Re: [dm-crypt] Exhaustive key reading seems to silently stop on error

[Milan Broz]

On 12/11/2009 11:57 AM, Nico R. wrote:

>>> In lib/utils.c (line 450f. in cryptsetup-1.0.7; line 490f. in current
>>> SVN revision, r132, equal to r152), we see the following code:
>>>
>>> if(read(fd, pass + i, 1) != 1 || (newline_stop && pass[i] == '\n'))
>>>         break;
>>>
>>> If I interpret that snipped (and its surroundings) correctly, the code
>>> will read until EOF *or* until an error occurs.

yes, sure it is bug, thanks for reporting it.

Fixed in trunk now
http://code.google.com/p/cryptsetup/source/detail?r=154#

Milan
--
mbroz@redhat.com