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[3.13] gh-127971: fix off-by-one read beyond the end of a string during search (#132574) #136648

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Merged
merged 1 commit into from
Jul 14, 2025
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[3.13] gh-127971: fix off-by-one read beyond the end of a string during search (#132574) #136648

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9 changes: 9 additions & 0 deletions Lib/test/string_tests.py
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Original file line number Diff line number Diff line change
Expand Up @@ -767,6 +767,15 @@ def test_replace(self):
self.checkraises(TypeError, 'hello', 'replace', 42, 'h')
self.checkraises(TypeError, 'hello', 'replace', 'h', 42)

def test_replacement_on_buffer_boundary(self):
# gh-127971: Check we don't read past the end of the buffer when a
# potential match misses on the last character.
any_3_nonblank_codepoints = '!!!'
seven_codepoints = any_3_nonblank_codepoints + ' ' + any_3_nonblank_codepoints
a = (' ' * 243) + seven_codepoints + (' ' * 7)
b = ' ' * 6 + chr(256)
a.replace(seven_codepoints, b)

def test_replace_uses_two_way_maxcount(self):
# Test that maxcount works in _two_way_count in fastsearch.h
A, B = "A"*1000, "B"*1000
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2025-04-16-12-01-13.gh-issue-127971.pMDOQ0.rst
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@@ -0,0 +1 @@
Fix off-by-one read beyond the end of a string in string search.
8 changes: 4 additions & 4 deletions Objects/stringlib/fastsearch.h
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Original file line number Diff line number Diff line change
Expand Up @@ -588,7 +588,7 @@ STRINGLIB(default_find)(const STRINGLIB_CHAR* s, Py_ssize_t n,
continue;
}
/* miss: check if next character is part of pattern */
if (!STRINGLIB_BLOOM(mask, ss[i+1])) {
if (i + 1 <= w && !STRINGLIB_BLOOM(mask, ss[i+1])) {
i = i + m;
}
else {
Expand All @@ -597,7 +597,7 @@ STRINGLIB(default_find)(const STRINGLIB_CHAR* s, Py_ssize_t n,
}
else {
/* skip: check if next character is part of pattern */
if (!STRINGLIB_BLOOM(mask, ss[i+1])) {
if (i + 1 <= w && !STRINGLIB_BLOOM(mask, ss[i+1])) {
i = i + m;
}
}
Expand Down Expand Up @@ -661,7 +661,7 @@ STRINGLIB(adaptive_find)(const STRINGLIB_CHAR* s, Py_ssize_t n,
}
}
/* miss: check if next character is part of pattern */
if (!STRINGLIB_BLOOM(mask, ss[i+1])) {
if (i + 1 <= w && !STRINGLIB_BLOOM(mask, ss[i+1])) {
i = i + m;
}
else {
Expand All @@ -670,7 +670,7 @@ STRINGLIB(adaptive_find)(const STRINGLIB_CHAR* s, Py_ssize_t n,
}
else {
/* skip: check if next character is part of pattern */
if (!STRINGLIB_BLOOM(mask, ss[i+1])) {
if (i + 1 <= w && !STRINGLIB_BLOOM(mask, ss[i+1])) {
i = i + m;
}
}
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