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Missing bounds-checks for VUI Bitstream Restriction Syntax Elements #55

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wrv opened this issue Jul 19, 2023 · 3 comments · May be fixed by #66
Open

Missing bounds-checks for VUI Bitstream Restriction Syntax Elements #55

wrv opened this issue Jul 19, 2023 · 3 comments · May be fixed by #66

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@wrv
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wrv commented Jul 19, 2023

The VUI bitstream restriction syntax elements are not bounds checked: https://github.com/dholroyd/h264-reader/blob/master/src/nal/sps.rs#L803-L812

Expected bounds, according to Annex E.2.1 of the spec:

  • max_bytes_per_pic_denom: [0, 16]
  • max_bits_per_mb_denom: [0, 16]
  • log2_max_mv_length_horizontal: [0, 15]
  • log2_max_mv_length_vertical: [0, 15]
  • max_num_reorder_frames: [0, max_dec_frame_buffering]
  • max_dec_frame_buffering: [max_num_reorder_frames, MaxDpbFrames] where MaxDpbFrames is set by the Level
dholroyd added a commit that referenced this issue Feb 26, 2024
@dholroyd
Bounds checks for bistream_restriction fields
549d4e6 
Fixes #55
@dholroyd dholroyd linked a pull request Feb 26, 2024 that will close this issue
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dholroyd added a commit that referenced this issue Feb 26, 2024
@dholroyd
Bounds checks for many fields
902104e 
Fixes #55, #58
@dholroyd
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log2_max_mv_length_horizontal: [0, 15]
log2_max_mv_length_vertical: [0, 15]

This is indeed what more recent versions of the standard specify, e.g. from 2017,

image

Looks like this changed at some point though. Bitstreams I've tested with use the value 16, and going back to a 2003 copy of the spec, it says 16,

image

I don't know when this changed.

It seems that to avoid rejecting real files, these checks should allow 16.

(Discussion of the same confusion on ffmpeg-devel.)

dholroyd added a commit that referenced this issue Feb 27, 2024
@dholroyd
Bounds checks for many fields
86a0ff9 
Fixes #55, #58
@wrv
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wrv commented Feb 27, 2024

Woah! Thanks for sharing this insight!

Are you familiar with any other syntax elements that have become more restrictive across spec versions?

@dholroyd
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I am not aware of other examples; but I would not have investigated if data already used in some tests hadn't been rejected by the new checks.

dholroyd added a commit that referenced this issue Feb 29, 2024
@dholroyd
Bounds checks for many fields
506ee23 
Fixes #55, #58
dholroyd added a commit that referenced this issue Mar 1, 2024
@dholroyd
Bounds checks for many fields
bacebcc 
Fixes #55, #58
dholroyd added a commit that referenced this issue Mar 1, 2024
@dholroyd
Bounds checks for many fields
ab5c4cb 
Fixes #55, #58
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Bounds checks for many fields dholroyd/h264-reader
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@dholroyd @wrv