[FFmpeg-devel] [PATCH] pngdec: check if previous frame exists instead of trusting sequence_number

[Michael Niedermayer]

On Sat, Nov 26, 2016 at 11:36:48PM +0100, Andreas Cadhalpun wrote:
> On 26.11.2016 01:53, Michael Niedermayer wrote:
> > On Fri, Nov 25, 2016 at 10:13:06PM +0100, Andreas Cadhalpun wrote:
> >> This fixes a segmentation fault caused by calling memcpy with NULL as
> >> second argument in handle_p_frame_apng.
> >>
> >> Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> >> ---
> >>  libavcodec/pngdec.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
> >> index 36275ae..a7b330b 100644
> >> --- a/libavcodec/pngdec.c
> >> +++ b/libavcodec/pngdec.c
> >> @@ -922,7 +922,7 @@ static int decode_fctl_chunk(AVCodecContext *avctx, PNGDecContext *s,
> >>          return AVERROR_INVALIDDATA;
> >>      }
> >>  
> >> -    if (sequence_number == 0 && dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
> >> +    if (!s->previous_picture.f->data[0] && dispose_op == APNG_DISPOSE_OP_PREVIOUS) {
> >>          // No previous frame to revert to for the first frame
> >>          // Spec says to just treat it as a APNG_DISPOSE_OP_BACKGROUND
> >>          dispose_op = APNG_DISPOSE_OP_BACKGROUND;
> > 
> > wont this be different when seeking back to the
> > first frame ?
> > is that intended ?
> 
> I don't think the apng demuxer supports seeking.
> But it shouldn't hurt to check both sequence_number and the previous frame.
> Updated patch is attached.
> 
> Best regards,
> Andreas
> 

>  pngdec.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 141d5230c97dbc47e0b291f660544cfe57abbf7c  0001-pngdec-check-if-previous-frame-exists-instead-of-tru.patch
> From 84125e5f32fd4b9146d9926d2f8a4467da7c8557 Mon Sep 17 00:00:00 2001
> From: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> Date: Fri, 25 Nov 2016 22:09:51 +0100
> Subject: [PATCH] pngdec: check if previous frame exists instead of trusting
>  sequence_number
> 
> This fixes a segmentation fault caused by calling memcpy with NULL as
> second argument in handle_p_frame_apng.
> 
> Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> ---
>  libavcodec/pngdec.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

LGTM

thx


[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.
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