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Fix heap buffer overflow in _tiffWriteProc when saving TIFF to BytesIO - #10224
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libtiff seeks past the current end of data when writing the directory and writes tag values there. _tiffWriteProc sized its realloc() from state->size + size instead of the write position state->loc + size, so the first out-of-line tag value written after such a seek could overrun the allocation by up to the size of the directory. The bytes skipped by the seek were also never zeroed, leaking stale heap contents into the saved file. Size the buffer from the write position and zero the space added by realloc, matching the semantics of writing to a real file. Reject writes where the position is still beyond the buffer for the non-reallocating case. Reported-by: carlini Reported-by: Tomer-PL Fixes: GHSA-332p-7hrc-92wf Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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libtiff seeks past the current end of data when writing the directory and writes tag values there. _tiffWriteProc sized its realloc() from state->size + size instead of the write position state->loc + size, so the first out-of-line tag value written after such a seek could overrun the allocation by up to the size of the directory. The bytes skipped by the seek were also never zeroed, leaking stale heap contents into the saved file.
Size the buffer from the write position and zero the space added by realloc, matching the semantics of writing to a real file. Reject writes where the position is still beyond the buffer for the non-reallocating case.