Re: [Xen-devel] Fix for SSP error in tools/python/lowlevel/xc/xc.c

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Aug 26, 2009 at 04:19:54PM +0200, Milan Holzäpfel wrote:
> Hello, 
> 
> I compiled xen-tools with GCC-4.3.3 with Stack Smashing Protection
> (SSP) patches by gentoo, and found a small bug in
> tools/python/lowlevel/xc/xc.c.  The bug is located in
> pyxc_dom_set_policy_cpuid: 
> 
> (this is the change which fixes it:)
> 
> > @@ -808,7 +808,7 @@
> >  static PyObject *pyxc_dom_set_policy_cpuid(XcObject *self,
> >                                             PyObject *args)
> >  {
> > -    domid_t domid;
> > +    int domid;

I would say use uint32_t instead of int.

> >  
> >      if ( !PyArg_ParseTuple(args, "i", &domid) )
> >          return NULL;
> 
> domid_t is defined as uint16_t (thus 2 bytes long) in xen header files,
> but the "i" format needs a C "int" type, which is 4 bytes long.
> (<URL:http://docs.python.org/c-api/arg.html>)  This error is detected
> by SSP as stack overflow. 

What about the two other cases where domid_it is used? The SSP didn't
detect them?
> 
> Attached patch fixes the error.  Maybe it would better to use "h"
> format instead of the "i" format, which converts the argument to an C
> "short int".  Then you would have to change the python wrapper if
> domid_t changes, though. 

Yeah, but running more than 64K of guests on one node?

> 
> Please apply this patch or the change to the "h" format string (I
> haven't tested it, but I believe it should work just as well). 
> 
> Regards,
> Milan Holzäpfel
> 
> 
> -- 
> Milan Holzaepfel <mail(a)mjh(d)name>             <URL:http://mjh.name/>
> pub  4096R/C790FC23  EB8E 5E81 81E3 53A9 9B74  B895 5179 54C0 C790 FC23

>       2009-08-26 Milan Holzaepfel <mail@xxxxxxxx>
> 
>       As documented on <URL:http://docs.python.org/c-api/arg.html>, the "i"
>       format string needs an integer as target.
> 
>       Error detected by gentoo Stack Smashing Protection for gcc-4.3.3.
> 
> --- xen-3.4.1/tools/python/xen/lowlevel/xc/xc.c.orig  2009-08-26 
> 13:43:13.000000000 +0000
> +++ xen-3.4.1/tools/python/xen/lowlevel/xc/xc.c       2009-08-26 
> 13:43:20.000000000 +0000
> @@ -808,7 +808,7 @@
>  static PyObject *pyxc_dom_set_policy_cpuid(XcObject *self,
>                                             PyObject *args)
>  {
> -    domid_t domid;
> +    int domid;
>  
>      if ( !PyArg_ParseTuple(args, "i", &domid) )
>          return NULL;




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