command: hashsum: md5sum reports wrong sum for the file named 4k.bin

[Sascha Hauer]

Hi Peter,

On Thu, Dec 21, 2017 at 01:48:11PM +0300, Peter Mamonov wrote:
> On Wed, Dec 20, 2017 at 01:48:14PM +0300, Peter Mamonov wrote:
> > Hi,
> > 
> > The md5sum command reports wrong sum for a file named 4k.bin and, I guess, for 
> > other files named alike. Here are the commands to reproduce the bug:
> 
> The problem lays in __do_digest() function: 
>  - it initializes variables `start` and `size` at commands/digest.c:38
>  - then it calls parse_area_spec(*argv, &start, &size) at commands/digest.c:42
>  - parse_area_spec() returns error as it should, however it changes the value 
>  of the `start` at lib/misc.c:87.
>  - this causes digest algo to skip leading 4k of the data from the file.
> 
> I'm not quite sure what is the best solution:
>  - prevent parse_area_spec() from setting start if it fails?
>  - reinitialize start/size after unsuccessfull call to parse_area_spec()?

preventing parse_area_spec() from modifying start and size if it fails
seems like a good idea.

However, this doesn't solve the problem, does it? parse_area_spec()
only fails because the dot in 4k.bin is not valid, but if you name
the file only '4k' then parse_area_spec() won't fail.
The problem is that we cannot know whether '4k' is a file or an area.

Right now I have no good idea how to make the command nonambiguous,
but this will require an incompatible change to the commands arguments.

Sascha


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