[Clamav-devel] Bug with .fp file being ignored

[Micah Snyder (micasnyd)]

Mark,

Well that’s embarrassing.  Looking at the patch now, it doesn’t seem like the right fix for the issue – given the remaining bug where it alerts and then reports clean afterwards.

It looks like cli_checkfp() is called within cli_append_virus(), and you’d think that would care of it – except that If you grep for “cli_append_virus”, you’ll notice that there are many cases where the return value is ignored.  I suspect the real issue is that most, if not all, of those cases should check that the return value is still CL_VIRUS to honor the verdict from cli_checkfp().

I’ll put in a ticket to investigate.

-Micah

From: clamav-devel <clamav-devel-bounces at lists.clamav.net> on behalf of Mark Allan <markjallan at gmail.com>
Reply-To: ClamAV Development <clamav-devel at lists.clamav.net>
Date: Friday, September 20, 2019 at 4:47 PM
To: ClamAV Development <clamav-devel at lists.clamav.net>
Subject: Re: [Clamav-devel] Bug with .fp file being ignored

Hi Micah,

Yes I did, and I submitted a patch back in July but there was another related issue which I wasn't able to fix.  I've copied my email below with the patches.

Best regards
Mark
---

The issue seems to have crept in with commits 3e42216cc and 28afc94c3 back in April/May 2017.

Attached are patches for devel/HEAD as well as the stable 0.101.2

Tests show that the issue is fixed and doesn't appear to introduce any false negatives.....however, it does produce a duplicate output line - one listed the infection found, and the second line (honouring the FP file) saying "OK".  The "infected files" count is correct - see output below.

Does anyone know how to fix that duplicate output?

Cheers
Mark

virus-2009-04-13-id0007662101.zip: Osx.Worm.Leap-2 FOUND
virus-2009-04-13-id0007662101.zip: OK

----------- SCAN SUMMARY -----------
Known viruses: 6168730
Engine version: 0.101.2
Scanned directories: 0
Scanned files: 1
Infected files: 0
Data scanned: 0.02 MB
Data read: 0.00 MB (ratio 0.00:1)
Time: 33.865 sec (0 m 33 s)



> On 20 Sep 2019, at 10:29 am, Micah Snyder (micasnyd) <micasnyd at cisco.com> wrote:
>
> Hi Mark,
>
> Did you have any luck identifying the source of the bug?  I admit I bookmarked your email and failed to find time to look into it myself after that.
>
> -Micah
>
> On 7/12/19, 6:09 PM, "clamav-devel on behalf of Mark Allan" <clamav-devel-bounces at lists.clamav.net on behalf of markjallan at gmail.com> wrote:
>
>    Hi,
>
>    I think there's a bug with ClamAV not honouring the contents of a .fp file
>    within the database directory.
>
>    I've tested 0.101.2 as well as previous versions of ClamAV going back to
>    0.99.4 and the issue seems to have appeared as of 0.100.0 onwards.
>
>    To re-create the issue:
>
>    Find a zip file which you know reports an infection when scanned.
>    Use sigtool --md5 to generate an FP sig of the zip file and save it in a
>    <filename>.fp file in the databse directory.
>    Use clamscan to scan the file and see that it still reports the file as
>    being infected.
>
>
>    The output from clamscan --debug shows the .fp file is being loaded, but it
>    just doesn't seem to be being honoured for some reason.
>
>    I see the same thing when I build ClamAV on macOS as well as when using the
>    apt-get distribution on Ubuntu 18.04
>
>    Lastly, it only appears to be an issue with archive filetypes eg .zip, .dmg
>    etc. Simple files are excluded as expected - similarly, if you generate an
>    FP sig of a simple file and put that file within an archive, it correctly
>    gets excluded.
>
>    I'll clone the source from Git on Monday and have a dig through it myself
>    to see if I can fix the bug, but thought I'd mention it here in case
>    someone's already on it, or at least knows where I can start looking!
>
>    Cheers
>    Mark
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>
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>
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>
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>
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>
>
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>
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>
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>
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> https://github.com/vrtadmin/clamav-faq
>
> http://www.clamav.net/contact.html#ml
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