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mpeg4dec: Ensure data is not clobbered too early.

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Avoid overwriting the bitstream buffer data before we
have ended processing the frame.
This is necessary to fix hwaccels which might try to use
the buffer during the end_frame call.
I am not sure but it is possible this could even trigger
a use-after-free if the av_fast_malloc allocated a new buffer.
This would require that decode_slice did not wind the bitstream
forward all the way to the end, which does not currently happen in
normal streams.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
This commit is contained in:
Reimar Döffinger 2013-09-19 01:08:30 +02:00
parent 6c169c2fa4
commit f76b633a94
1 changed files with 12 additions and 11 deletions
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23
libavcodec/h263dec.c
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@ -672,7 +672,7 @@ retry:
if (CONFIG_WMV2_DECODER && s->msmpeg4_version==5){
ret = ff_wmv2_decode_secondary_picture_header(s);
if(ret<0) return ret;
if(ret==1) goto intrax8_decoded;
if(ret==1) goto frame_end;
}
/* decode each macroblock */
@ -705,7 +705,18 @@ retry:
av_assert1(s->bitstream_buffer_size==0);
frame_end:
ff_er_frame_end(&s->er);
if (avctx->hwaccel) {
if ((ret = avctx->hwaccel->end_frame(avctx)) < 0)
return ret;
}
ff_MPV_frame_end(s);
/* divx 5.01+ bitstream reorder stuff */
/* Since this clobbers the input buffer and hwaccel codecs still need the
* data during hwaccel->end_frame we should not do this any earlier */
if(s->codec_id==AV_CODEC_ID_MPEG4 && s->divx_packed){
int current_pos= s->gb.buffer == s->bitstream_buffer ? 0 : (get_bits_count(&s->gb)>>3);
int startcode_found=0;
@ -732,16 +743,6 @@ frame_end:
}
}
intrax8_decoded:
ff_er_frame_end(&s->er);
if (avctx->hwaccel) {
if ((ret = avctx->hwaccel->end_frame(avctx)) < 0)
return ret;
}
ff_MPV_frame_end(s);
if (!s->divx_packed && avctx->hwaccel)
ff_thread_finish_setup(avctx);