Xen devel - Jun 2005 - [PATCH] proper bounds check in do_set_gdt entry point

Unless I missed something, not bounds checking entries in do_set_gdt is 
a security hole.

Signed-off-by: Chris Wright <chrisw@osdl.org>

--- 1.184/xen/arch/x86/mm.c	2005-06-23 02:35:56 -07:00
+++ edited/xen/arch/x86/mm.c	2005-06-27 11:37:30 -07:00
@@ -2442,6 +2442,9 @@ long do_set_gdt(unsigned long *frame_lis
     unsigned long frames[16];
     long ret;
 
+    if ( entries > FIRST_RESERVED_GDT_ENTRY )
+        return -EINVAL;
+
     if ( copy_from_user(frames, frame_list, nr_pages * sizeof(unsigned long)) )
         return -EFAULT;
 

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

On 27 Jun 2005, at 19:41, Chris Wright wrote:
> Unless I missed something, not bounds checking entries in do_set_gdt is
> a security hole.
>
> Signed-off-by: Chris Wright <chrisw@osdl.org>
The check happens in set_gdt(). do_set_gdt is just a wrapper with a 
copy_from_user plus conditional tlb flush.

  -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

* Keir Fraser (Keir.Fraser@cl.cam.ac.uk) wrote:
> 
> On 27 Jun 2005, at 19:41, Chris Wright wrote:
> 
> >Unless I missed something, not bounds checking entries in do_set_gdt is
> >a security hole.
> >
> >Signed-off-by: Chris Wright <chrisw@osdl.org>
> 
> The check happens in set_gdt(). do_set_gdt is just a wrapper with a 
> copy_from_user plus conditional tlb flush.
I know, but copy_from_user has no sane limits.  This is stack smash.
-chris

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

On 27 Jun 2005, at 21:00, Chris Wright wrote:
>> The check happens in set_gdt(). do_set_gdt is just a wrapper with a
>> copy_from_user plus conditional tlb flush.
>
> I know, but copy_from_user has no sane limits.  This is stack smash.
> -chris
Good point.

  -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel