[FFmpeg-devel] [PATCH v1] avcodec/h2645_parse: fix for the realloc size

[Limin Wang]

On Tue, Sep 10, 2019 at 12:03:14AM -0300, James Almer wrote:
> On 9/9/2019 11:51 PM, Limin Wang wrote:
> > On Mon, Sep 09, 2019 at 10:53:53PM -0300, James Almer wrote:
> >> On 9/9/2019 10:18 PM, lance.lmwang at gmail.com wrote:
> >>> From: Limin Wang <lance.lmwang at gmail.com>
> >>>
> >>> Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> >>> ---
> >>>  libavcodec/h2645_parse.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/libavcodec/h2645_parse.c b/libavcodec/h2645_parse.c
> >>> index 307e8643e6..403acd2ee1 100644
> >>> --- a/libavcodec/h2645_parse.c
> >>> +++ b/libavcodec/h2645_parse.c
> >>> @@ -454,7 +454,7 @@ int ff_h2645_packet_split(H2645Packet *pkt, const uint8_t *buf, int length,
> >>>          }
> >>>  
> >>>          if (pkt->nals_allocated < pkt->nb_nals + 1) {
> >>> -            int new_size = pkt->nals_allocated + 1;
> >>> +            int new_size = pkt->nb_nals + 1;
> >>
> >> No. nals_allocated and nb_nals are two purposely separate values in
> >> order to reuse the H2645Packet struct. One keeps track of the allocated
> >> size of the NAL buffer, whereas the other keeps track of the amount of
> >> NALs used by the current packet. That's why the check immediately above
> >> this line makes sure the amount of NALs in the current packet fit in the
> >> current size of the NAL buffer, and grows/reallocates it otherwise.
> > 
> > Thanks for the detail information about the two field. Below is my assumation 
> > as I haven't such sample to test such case.
> > Assuming nals_allocated is 1, nb_nals is 3
> 
> That can't happen. nb_nals is always set to zero at the start of
> ff_h2645_packet_split(), and is increased by one every time a NAL is
> finished parsing. It's guaranteed to always be less or equal than
> nals_allocated by the above check.
> 
> , then the current code will reallocate

Thanks, it's clear now. I have small change to get better code readiablity(which I think)


> > new_size with 2, But the following code will use the nb_nals to access pkt->nals, 
> > I'm not sure nals memory is allocated or not?
> > nal = &pkt->nals[pkt->nb_nals];
> > 
> > 
> >>
> >>>              void *tmp = av_realloc_array(pkt->nals, new_size, sizeof(*pkt->nals));
> >>>  
> >>>              if (!tmp)
> >>>
> >>
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> 
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