[3.13] gh-144759: Fix undefined behavior from NULL pointer arithmetic in lexer (GH-144788)#145355
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pablogsal merged 1 commit intopython:3.13from Feb 28, 2026
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…hmetic in lexer (pythonGH-144788) Guard against NULL pointer arithmetic in `_PyLexer_remember_fstring_buffers` and `_PyLexer_restore_fstring_buffers`. When `start` or `multi_line_start` are NULL (uninitialized in tok_mode_stack[0]), performing `NULL - tok->buf` is undefined behavior. Add explicit NULL checks to store -1 as sentinel and restore NULL accordingly. Add test_lexer_buffer_realloc_with_null_start to test_repl.py that exercises the code path where the lexer buffer is reallocated while tok_mode_stack[0] has NULL start/multi_line_start pointers. This triggers _PyLexer_remember_fstring_buffers and verifies the NULL checks prevent undefined behavior. (cherry picked from commit e6110ef) Co-authored-by: Ramin Farajpour Cami <ramin.blackhat@gmail.com>
This was referenced Feb 28, 2026
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johnslavik
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Thanks a lot @StanFromIreland |
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Guard against NULL pointer arithmetic in
_PyLexer_remember_fstring_buffersand_PyLexer_restore_fstring_buffers. Whenstartormulti_line_startare NULL (uninitialized in tok_mode_stack[0]), performingNULL - tok->bufis undefined behavior. Add explicit NULL checks to store -1 as sentinel and restore NULL accordingly.Add test_lexer_buffer_realloc_with_null_start to test_repl.py that exercises the code path where the lexer buffer is reallocated while tok_mode_stack[0] has NULL start/multi_line_start pointers. This triggers _PyLexer_remember_fstring_buffers and verifies the NULL checks prevent undefined behavior.
(cherry picked from commit e6110ef)