Xen devel - Jun 2010 - [PATCH] libxc: Fix Segmentation fault of xend

If /proc/xen/privcmd cannot be opened,
start xend occurs Segmentation fault.
Add check to fix it.

Signed-off-by: Yu Zhiguo <yuzg@cn.fujitsu.com>

diff -r b9c541d9c138 -r 659e4b69d26b tools/libxc/xc_private.c
--- a/tools/libxc/xc_private.c	Tue Jun 15 13:27:14 2010 +0100
+++ b/tools/libxc/xc_private.c	Sat Jun 19 22:24:09 2010 +0800
@@ -82,8 +82,10 @@
 
 void xc_clear_last_error(xc_interface *xch)
 {
-    xch->last_error.code = XC_ERROR_NONE;
-    xch->last_error.message[0] = ''\0'';
+    if (xch) {
+        xch->last_error.code = XC_ERROR_NONE;
+        xch->last_error.message[0] = ''\0'';
+    }
 }
 
 const char *xc_error_code_to_desc(int code)


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Yu Zhiguo writes ("[Xen-devel] [PATCH] libxc: Fix Segmentation fault of
xend"):
> If /proc/xen/privcmd cannot be opened,
> start xend occurs Segmentation fault.
> Add check to fix it.
This change is not correct.
>  void xc_clear_last_error(xc_interface *xch)
...
> -    xch->last_error.message[0] = ''\0'';
> +    if (xch) {
It is wrong to call xc_clear_last_error with a NULL xc_interface*.
If xend is doing this it is probably a bug in the python xc lowlevel
interface.  Can you get a stack trace please so that we can fix the
call site ?

Nacked-by: Ian Jackson <ian.jackson@eu.citrix.com>

Ian.

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I wrote:
> Nacked-by: Ian Jackson <ian.jackson@eu.citrix.com>
I see that, unfortunately, this patch has already been applied.

Ian.

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On 21/06/2010 15:03, "Ian Jackson" <Ian.Jackson@eu.citrix.com>
wrote:
> I wrote:
>> Nacked-by: Ian Jackson <ian.jackson@eu.citrix.com>
> 
> I see that, unfortunately, this patch has already been applied.
I can revert it.

 -- Keir
> Ian.


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Keir Fraser writes ("Re: [Xen-devel] [PATCH] libxc: Fix Segmentation fault
of xend"):
> On 21/06/2010 15:03, "Ian Jackson"
<Ian.Jackson@eu.citrix.com> wrote:
> > I wrote:
> >> Nacked-by: Ian Jackson <ian.jackson@eu.citrix.com>
> > 
> > I see that, unfortunately, this patch has already been applied.
> 
> I can revert it.
Thanks, I think that would be best.

Ian.

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Hi Ian,

Ian Jackson wrote:
> 
> It is wrong to call xc_clear_last_error with a NULL xc_interface*.
> If xend is doing this it is probably a bug in the python xc lowlevel
> interface.  Can you get a stack trace please so that we can fix the
> call site ?
> 

The stack trace is
 PyXc_init()
  -> pyxc_error_to_exception(0)
   -> xc_clear_last_error()

So fix it in pyxc_error_to_exception(). Thanks for your reply.

V2 is following.

-----------------

If /proc/xen/privcmd cannot be opened,
start xend occurs Segmentation fault.
Add check to fix it.

Signed-off-by: Yu Zhiguo <yuzg@cn.fujitsu.com>

diff -r 72c6228b5f0f -r bd3bf925f4ce tools/python/xen/lowlevel/xc/xc.c
--- a/tools/python/xen/lowlevel/xc/xc.c	Mon Jun 21 19:19:25 2010 +0100
+++ b/tools/python/xen/lowlevel/xc/xc.c	Tue Jun 22 17:02:30 2010 +0800
@@ -72,7 +72,8 @@
     else
         pyerr = Py_BuildValue("(is)", err->code, desc);
 
-    xc_clear_last_error(xch);
+    if (xch)
+        xc_clear_last_error(xch);
 
     if ( pyerr != NULL )
     {


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Yu Zhiguo writes ("Re: [Xen-devel] [PATCH] lowlevel: Fix Segmentation fault
of xend"):
> The stack trace is
>  PyXc_init()
>   -> pyxc_error_to_exception(0)
>    -> xc_clear_last_error()
> 
> So fix it in pyxc_error_to_exception(). Thanks for your reply.
That''s great, thanks.

Ian.

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