Re: [Xen-devel] [PATCH v2 for-4.7 07/14] libxc: fix uninitialized variable

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 27/04/16 09:57, Roger Pau Monne wrote:
> On Tue, Apr 26, 2016 at 04:16:51PM +0100, Wei Liu wrote:
>> On Tue, Apr 26, 2016 at 04:52:16PM +0200, Roger Pau Monne wrote:
>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>> ---
>>> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
>>> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
>>> ---
>>>  tools/libxc/xc_dom_bzimageloader.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/tools/libxc/xc_dom_bzimageloader.c 
>>> b/tools/libxc/xc_dom_bzimageloader.c
>>> index 7fde42a..0a4041c 100644
>>> --- a/tools/libxc/xc_dom_bzimageloader.c
>>> +++ b/tools/libxc/xc_dom_bzimageloader.c
>>> @@ -482,7 +482,7 @@ static int xc_try_lzo1x_decode(
>>>          if ( !dst_len )
>>>          {
>>>              msg = "Error registering stream output";
>>> -            if ( xc_dom_register_external(dom, out_buf, out_len) )
>>> +            if ( xc_dom_register_external(dom, out_buf, 0) )
>> I fail to figure out why this is correct.
>>
>> I think the out_len should be moved out of the loop and initialise as 0.
>> We still need to use out_len here.
> I'm not following here. AFAICT out_len is always uninitialized at this 
> point (from loop 0 to N), so I assume 0 is what was intended to be passed 
> here. Or it this supposed to be passing in the last out_len value from the 
> previous iteration of the loop?

xc_dom_register_external() is completely mad, and it is not obvious as
to its purpose; tt is doing some kind of allocation tracking for
malloc()-allocated blocks.   It looks like the output length is only
uses for stats purposes, as the memory in out_buf will be freed properly
by free().

So I think the correct value should be the actual size of the allocation
of out_buf, but I also don't think it makes any real difference either way.

~Andrew

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