Re: Hooking exec system call

[rohan puri <rohan.puri15@xxxxxxxxx>]

On Mon, Sep 26, 2011 at 12:29 PM, Abhijit Pawar <apawar.linux@xxxxxxxxx> wrote:

On 09/26/2011 12:26 PM, rohan puri wrote:

On Mon, Sep 26, 2011 at 12:02 PM, Abhijit Pawar <apawar.linux@xxxxxxxxx> wrote:

On 09/23/2011 03:11 PM, rohan puri wrote:

On Fri, Sep 23, 2011 at 2:43 PM, Abhijit Pawar <apawar.linux@xxxxxxxxx> wrote:

On 09/23/2011 02:04 PM, rohan puri wrote:

On Fri, Sep 23, 2011 at 2:00 PM, Abhijit Pawar <apawar.linux@xxxxxxxxx> 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@xxxxxxxxx>  wrote:

On Thu, Sep 22, 2011 at 1:53 PM, Abhijit Pawar<apawar.linux@xxxxxxxxx>
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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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

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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 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

Hi Abhijit,

I am not familiar with windows. Special use-case of this hacking is for security companies whitelisting software solutions, where they want to control execution of only authorized binaries on the system and deny the execution of others.


Although this approach is untidy, since there is available LSM hooks in linux kernel which needs to be made use of for doing this.

Regards,
Rohan Puri

Hi Rohan,
Yes, this is a backdoor approach and I agree with you. I am learning more on LSM and their APIs so as to get insight into what goes on internally. May be you can refer me to some details as well.

Thanks for all of your help on this.

Regards,
Abhijit Pawar

Hi Abhijit,

There is one whitepaper of lsm available on internet by Greg Kroah-Hartman and others, its good to start with.


Also, I am keen to now, do all these things you are studying are part of any project or just for knowledge.

Regards,
Rohan Puri
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