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Re: [Xen-devel] [PATCH] libxenlight: fix heap overflow when domid_to_nam

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] libxenlight: fix heap overflow when domid_to_name returns NULL
From: Eamon Walsh <ewalsh@xxxxxxxxxxxxx>
Date: Mon, 07 Mar 2011 10:33:03 -0500
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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On 03/04/2011 05:02 AM, Ian Campbell wrote:
> On Thu, 2011-03-03 at 23:29 +0000, Eamon Walsh wrote:
>> The function flexarray_vappend() will stop at the first NULL
>> argument.  In libxl_device_vfb_add(), this has been observed
>> to result in keys being added to the backend array without
>> associated values in cases where the value can be NULL.
> If these values are NULL should we be writing them at all? e.g. for:
>       flexarray_vappend(back, foo, bar);
> where bar may be NULL shouldn't it become:
>       if (bar) 
>               flexarray_vappend(back, foo, bar);
> or perhaps:
>       flexarray_vappend(back, foo, bar ? bar : "");
> ?

If the value is NULL, the key is skipped and not written.  This is because of a 
patch I submitted to change the xs_writev() function, which was calling 
strlen(NULL) previously.  See:

However this behavior is not obvious.  Checking the value earlier and leaving 
it off the list makes sense.


Eamon Walsh 
National Security Agency

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