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SubjectRe: [RFC PATCH 1/6] hv_sock: Check hv_pkt_iter_first_raw()'s return value
On Fri, Apr 15, 2022 at 03:33:23AM +0000, Michael Kelley (LINUX) wrote:
> From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Wednesday, April 13, 2022 1:48 PM
> >
> > The function returns NULL if the ring buffer has no enough space
> > available for a packet descriptor. The ring buffer's write_index
>
> The first sentence wording is a bit scrambled. I think you mean the
> ring buffer doesn't contain enough readable bytes to constitute a
> packet descriptor.

Indeed, replaced with your working.


> > is in memory which is shared with the Hyper-V host, its value is
> > thus subject to being changed at any time.
>
> This second sentence is true, but I'm not making the connection
> with the code change below. Evidently, there is some previous
> check made to ensure that enough bytes are available to be
> received when hvs_stream_dequeue() is called, so we assumed that
> NULL could never be returned? I looked but didn't find such a check,
> so maybe I didn't look carefully enough. But now we are assuming
> that Hyper-V might have invalidated that previous check by
> subsequently changing the write_index in a bogus way? So now, NULL
> could be returned when previously we assumed it couldn't.

I think you're looking for hvs_stream_has_data(). (Previous checks
apart, hvs_stream_dequeue() will "dereference" the pointer so...)

Thanks,
Andrea

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