Hooking exec system call

[Abhijit Pawar]

On 09/23/2011 03:11 PM, rohan puri wrote:
>
>
> On Fri, Sep 23, 2011 at 2:43 PM, Abhijit Pawar <apawar.linux at gmail.com 
> <mailto:apawar.linux at gmail.com>> wrote:
>
>     On 09/23/2011 02:04 PM, rohan puri wrote:
>>
>>
>>     On Fri, Sep 23, 2011 at 2:00 PM, Abhijit Pawar
>>     <apawar.linux at gmail.com <mailto:apawar.linux at gmail.com>> wrote:
>>
>>         On 09/23/2011 01:01 PM, Rajat Sharma wrote:
>>
>>                 Untidy way : -
>>                 Yes, you can do that by registering a new binary
>>                 format handler. Whenever
>>                 exec is called, a list of registered binary format
>>                 handlers is scanned, in
>>                 the same way you can hook the load_binary&
>>                  load_library function pointers
>>                 of the already registered binary format handlers.
>>
>>             Challenge with this untidy way is to identify the correct
>>             format, for
>>             example if you are interested in only hooking ELF format,
>>             there is no
>>             special signature withing the registered format handler
>>             to identify
>>             that, however if one format handler recognizes the file
>>             header, its
>>             load_binary will return 0. This can give you the hint
>>             that you are
>>             sitting on top of correct file format. Long time back I
>>             had written
>>             the similar module in Linux to do the same, but can't
>>             share the code
>>             :)
>>
>>             -Rajat
>>
>>             On Thu, Sep 22, 2011 at 3:14 PM, rohan
>>             puri<rohan.puri15 at gmail.com
>>             <mailto:rohan.puri15 at gmail.com>>  wrote:
>>
>>
>>                 On Thu, Sep 22, 2011 at 1:53 PM, Abhijit
>>                 Pawar<apawar.linux at gmail.com
>>                 <mailto:apawar.linux at gmail.com>>
>>                 wrote:
>>
>>                     hi list,
>>                     Is there any way to hook the exec system call on
>>                     Linux box apart from
>>                     replacing the call in System Call table?
>>
>>                     Regards,
>>                     Abhijit Pawar
>>
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>>                     <mailto:Kernelnewbies at kernelnewbies.org>
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>>
>>                 Tidy way : -
>>
>>                 You can do that from LSM (Linux security module).
>>
>>                 Untidy way : -
>>                 Yes, you can do that by registering a new binary
>>                 format handler. Whenever
>>                 exec is called, a list of registered binary format
>>                 handlers is scanned, in
>>                 the same way you can hook the load_binary&
>>                  load_library function pointers
>>                 of the already registered binary format handlers.
>>
>>                 Regards,
>>                 Rohan Puri
>>
>>                 _______________________________________________
>>                 Kernelnewbies mailing list
>>                 Kernelnewbies at kernelnewbies.org
>>                 <mailto:Kernelnewbies at kernelnewbies.org>
>>                 http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>
>>
>>         So If I use the binary format handler, then I can hook the
>>         exec call. however I need to register this. Does that mean
>>         that I need to return the negative value so as to have actual
>>         ELF handler to be loaded?
>>
>>         Regards,
>>         Abhijit Pawar
>>
>>     Read this, http://www.linux.it/~rubini/docs/binfmt/binfmt.html
>>     <http://www.linux.it/%7Erubini/docs/binfmt/binfmt.html> this
>>     might help
>>
>>     Regards,
>>     Rohan Puri
>     Thanks Rohan. I tried creating a hooking module on the similar
>     line. I am able to load the module but whenever I am launching any
>     application , its load_binary is not being called.
>     here is the source for the module attached.
>
>     Regards,
>     Abhijit Pawar
>
>
>
> Hi Abhijit,
>
> I have made the change, try to compile and execute this code, it works.
>
> Also, I am just curious enough to know that where do you need to do 
> this hooking.
>
> Regards,
> Rohan Puri
Hi Rohan,
I have been looking at Windows worlds ability to support DLL Injection 
and API hooking. I was just wondering if this could be something to be 
done in Linux as well.  I am not sure if there is any special use of 
this module apart from learning the binary handler. May be it could be 
used as a security module for your own binary handler.

Regards,
Abhijit Pawar
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