Re: [Xen-devel] [PATCH 1/2] gnttab: correct GNTTABOP_cache_flush empty batch handling

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.12.17 at 16:31, <andre.przywara@xxxxxxxxxx> wrote:
> On 30/11/17 14:31, Jan Beulich wrote:
>> Jann validly points out that with a caller bogusly requesting a zero-
>> element batch with non-zero high command bits (the ones used for
>> continuation encoding), the assertion right before the call to
>> hypercall_create_continuation() would trigger. A similar situation would
>> arise afaict for non-empty batches with op and/or length zero in every
>> element.
>> 
>> While we want the former to succeed (as we do elsewhere for similar
>> no-op requests), the latter can clearly be converted to an error, as
>> this is a state that can't be the result of a prior operation.
>> 
>> Take the opportunity and also correct the order of argument checks:
>> We shouldn't accept zero-length elements with unknown bits set in "op".
>> Also constify cache_flush()'s first parameter.
>> 
>> Reported-by: Jann Horn <jannh@xxxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Took me a while to wrap my head around it, because the actual fix is
> just the "*cur_ref = 0;" line, I think.
> But this looks correct to me.
> 
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxxxxx>

I guess this was meant to be Reviewed-by?

Jan


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