gh-144759: Fix undefined behavior from NULL pointer arithmetic in lexer#144788
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raminfp wants to merge 3 commits intopython:mainfrom
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gh-144759: Fix undefined behavior from NULL pointer arithmetic in lexer#144788raminfp wants to merge 3 commits intopython:mainfrom
raminfp wants to merge 3 commits intopython:mainfrom
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…in lexer 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.
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…tions Replace :c:func: references with double-backtick markup since these are internal functions without documentation entries.
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@raminfp Could you add a regression test? I suspect And please avoid force pushes to the PR so we preserve history. |
…exer 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.
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Fix undefined behavior in
_PyLexer_remember_fstring_buffersand_PyLexer_restore_fstring_bufferscaused by performing pointer arithmetic onNULLpointers (NULL - tok->buf).When
tok_mode_stack[0]is initialized, thestartandmulti_line_startfields are not explicitly set and remainNULL(fromPyMem_Calloc). Later, when the lexer buffer is reallocated, the remember/restore functions performNULL - valid_pointerandvalid_pointer + negative_offset, both of which are undefined behavior in C.The fix adds explicit
NULLchecks: store-1as a sentinel offset when the pointer isNULL, and restoreNULLwhen the offset is negative.Detected with
--with-undefined-behavior-sanitizer:Fixes #144759