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Date: Mon, 8 Apr 2002 09:27:37 +0300
From: Muli Ben-Yehuda <mulix@actcom.co.il>
To: Anton Altaparmakov <aia21@cam.ac.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
        John Levon <movement@marcelothewonderpenguin.com>,
        "Steven N. Hirsch" <shirsch@adelphia.net>,
        linux-kernel@vger.kernel.org
Subject: Re: Two fixes for 2.4.19-pre5-ac3
Message-ID: <20020408092737.D10733@actcom.co.il>
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On Mon, Apr 08, 2002 at 12:03:06AM +0100, Anton Altaparmakov wrote:
> At 21:23 07/04/02, Muli Ben-Yehuda wrote:

> >Right, this module (syscall_hijack.o) currently has the interface:
> >
> >int hijack_syscall_before(int syscall_id, func_ptr func);
> >int hijack_syscall_after(int syscall_id, func_ptr func);
> >
> >int release_syscall_before(int syscall_id);
> >int release_syscall_after(int syscall_id);
> >
> >where 'before' and 'after' correspond to a hook which should run
> >before the original system call is invoked (allowing it to specify
> >that the original system call should not be executed) or after the
> >original system call is invoked (allowing it access to its return
> >value).
> [snip]
> 
> So are you coping with someone hijacking YOU as well between calls to 
> hijack_syscall_* and release_syscall_*? Or would that trash the
> caller chain?

That should work fine, since we never explicitly refer to the entry in
the sys_call_table in our call chain (our callchain goes 

hijacked_function 
   -> hook_before
   if call original syscall
   ->  original syscall (the entry that was in the sys_call_table when we
       hijacked it, not the currrent entry!)
   -> hook_after

Note that we don't support stacking of hooks right now - we never had
need to. 
-- 
The ill-formed Orange
Fails to satisfy the eye:       http://vipe.technion.ac.il/~mulix/
Segmentation fault.             http://syscalltrack.sf.net/
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