Fix subsampled row addressing in generic_unpack for multi-line chunks#2543
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Fix subsampled row addressing in generic_unpack for multi-line chunks#2543cary-ilm wants to merge 1 commit into
cary-ilm wants to merge 1 commit into
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generic_unpack() tests row membership with the absolute file row (cury = y + chunk.start_y) but computed the compact FrameBuffer destination using the chunk-local row (y - user_line_begin_skip). For multi-line compressed chunks such as ZIP's 16-line blocks, later chunks often begin at a file row that is not a multiple of ySampling. The first sampled row in such a chunk then has a non-zero chunk-local index, and (y - uls) / y_samples truncates to the wrong compact row. Decoded rows land in the wrong buffer rows and the last sampled row may remain stale. Compute the destination offset relative to decode_to_ptr, which callers already position at the compact row for the current read origin (fb_y = user_line_begin_skip + chunk.start_y): (cury / y_samples - fb_y / y_samples) * user_line_stride Addresses https://github.com/AcademySoftwareFoundation/openexr/security/advisories/GHSA-7828-c4f6-7v6p Signed-off-by: Cary Phillips <cary@ilm.com> Co-authored-by: Cursor <cursoragent@cursor.com>
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generic_unpack() tests row membership with the absolute file row (cury = y + chunk.start_y) but computed the compact FrameBuffer destination using the chunk-local row (y - user_line_begin_skip). For multi-line compressed chunks such as ZIP's 16-line blocks, later chunks often begin at a file row that is not a multiple of ySampling. The first sampled row in such a chunk then has a non-zero chunk-local index, and (y - uls) / y_samples truncates to the wrong compact row. Decoded rows land in the wrong buffer rows and the last sampled row may remain stale.
Compute the destination offset relative to decode_to_ptr, which callers already position at the compact row for the current read origin (fb_y = user_line_begin_skip + chunk.start_y):
(cury / y_samples - fb_y / y_samples) * user_line_stride
Addresses https://github.com/AcademySoftwareFoundation/openexr/security/advisories/GHSA-7828-c4f6-7v6p