[FFmpeg-devel] [PATCH 05/11] avformat/nutenc: Don't pass NULL to memcmp

[Michael Niedermayer]

On Thu, Oct 31, 2019 at 07:38:00AM +0000, Andreas Rheinhardt wrote:
> Andreas Rheinhardt:
> > Carl Eugen Hoyos:
> >> Am Fr., 20. Sept. 2019 um 00:30 Uhr schrieb Andreas Rheinhardt
> >> <andreas.rheinhardt at gmail.com>:
> >>>
> >>> Fixes lots of FATE tests, e.g. lavf-nut, as well as the nut part of
> >>> ticket #7980.
> >>>
> >>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> >>> ---
> >>> This patch is made to match the previous behaviour; whether the previous
> >>> behaviour is correct at all if the header length is zero is unknown to
> >>> me.
> >>>
> >>>  libavformat/nutenc.c | 5 +++--
> >>>  1 file changed, 3 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/libavformat/nutenc.c b/libavformat/nutenc.c
> >>> index e9a3bb49db..dc714eb809 100644
> >>> --- a/libavformat/nutenc.c
> >>> +++ b/libavformat/nutenc.c
> >>> @@ -791,8 +791,9 @@ static int get_needed_flags(NUTContext *nut, StreamContext *nus, FrameCode *fc,
> >>>          flags |= FLAG_CHECKSUM;
> >>>      if (pkt->size < nut->header_len[fc->header_idx] ||
> >>>          (pkt->size > 4096 && fc->header_idx)        ||
> >>> -        memcmp(pkt->data, nut->header[fc->header_idx],
> >>> -               nut->header_len[fc->header_idx]))
> >>> +        (nut->header_len[fc->header_idx] > 0 &&
> >>> +         memcmp(pkt->data, nut->header[fc->header_idx],
> >>> +                nut->header_len[fc->header_idx])))
> >>>          flags |= FLAG_HEADER_IDX;
> >>
> >> Is this different from the patch I sent?
> >> (Why does it look different)
> >> https://patchwork.ffmpeg.org/patch/13782/
> >>
> >> Carl Eugen
> > 
> > Yes.
> > a) Your patch checks whether nut->header[fc->header_idx] is NULL.
> > b) Michael's proposal is to check for fc->header_idx instead. This
> > would work, because it is the index of the only used pointer in
> > nut->header that is NULL, and this proposal has the advantage of one
> > dereferencing less than a).
> > c) My* patch checks whether nut->header_len[fc->header_idx] is zero.
> > Given that nut->header_len[fc->header_idx] is already used in the very
> > first check, my solution should not entail a dereference at all.
> > 
> > Furthermore, b) is very specific to the nutenc situation here and a)
> > might hide a situation where nut->header_len[fc->header_idx] is > 0,
> > but nut->header[fc->header_idx] == NULL, which should of course not
> > happen. And it singles out one of the two pointer arguments.
> > 
> > - Andreas
> > 
> > *: It is also what Reimar proposed (I was completely unaware of the
> > earlier patch when I submitted mine).
> > 
> Ping.

I dont think the resulting code is particularly readable with the
increasingly complex condition in the if()

ill post a alternative suggestion for consideration that has a simpler
condition after testing it

thx

[...]
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