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gh-97556: Fix crash on null characters in string literal parser #97577

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gh-97556: Fix crash on null characters in string literal parser #97577

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7d1d3e9
String parser no longer crashes on null characters
apccurtiss Sep 26, 2022
15dfa85
Removed test, which is blocked by issue #96670
apccurtiss Sep 26, 2022
883f6f5
Moved the INT_MAX length check to the top of the string parser.
apccurtiss Sep 26, 2022
d62c4e2
📜🤖 Added by blurb_it.
blurb-it[bot] Sep 26, 2022
7f37169
Fix CI: move news entry out of spaced directory (gh-96670)
ambv Oct 21, 2026
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2022-09-26-16-46-54.gh-issue-96670.-n9hqb.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix interpreter crash when a string literal contains a null character.

@pablogsal pablogsal Jun 29, 2026

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Nit: this NEWS entry is filed under gh-issue-96670, but this PR fixes gh-97556. Can we rename it so the changelog points to the right issue?

21 changes: 13 additions & 8 deletions Parser/string_parser.c
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Expand Up @@ -249,12 +249,18 @@ _PyPegen_decode_string(Parser *p, int raw, const char *s, size_t len, Token *t)
PyObject *
_PyPegen_parse_string(Parser *p, Token *t)
{
const char *s = PyBytes_AsString(t->bytes);
if (s == NULL) {
char *s;
Py_ssize_t len;

if (PyBytes_AsStringAndSize(t->bytes, &s, &len)) {

@pablogsal pablogsal Jun 29, 2026

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Shouldn't we reject this in the tokenizer instead? Otherwise files with NUL bytes in a string literal become valid source, while compile() still rejects NUL bytes.

@pablogsal pablogsal Jun 29, 2026

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This is a crash fix but it lands without a regression test. I know a .py file with a null byte is blocked by gh-96670, but can we still add a regression test somehow, e.g. compiling a bytes source with an embedded null? We really want to keep this from regressing.

return NULL;
}

if (len > INT_MAX) {
PyErr_SetString(PyExc_OverflowError, "string to parse is too long");
return NULL;
}

size_t len;
int quote = Py_CHARMASK(*s);
int bytesmode = 0;
int rawmode = 0;
Expand All @@ -263,13 +269,16 @@ _PyPegen_parse_string(Parser *p, Token *t)
while (!bytesmode || !rawmode) {
if (quote == 'b' || quote == 'B') {
quote =(unsigned char)*++s;
len--;
bytesmode = 1;
}
else if (quote == 'u' || quote == 'U') {
quote = (unsigned char)*++s;
len--;
}
else if (quote == 'r' || quote == 'R') {
quote = (unsigned char)*++s;
len--;
rawmode = 1;
}
else {
Expand All @@ -285,15 +294,11 @@ _PyPegen_parse_string(Parser *p, Token *t)

/* Skip the leading quote char. */
s++;
len = strlen(s);
len--;
// gh-120155: 's' contains at least the trailing quote,
// so the code '--len' below is safe.
assert(len >= 1);

if (len > INT_MAX) {
PyErr_SetString(PyExc_OverflowError, "string to parse is too long");
return NULL;
}
if (s[--len] != quote) {
/* Last quote char must match the first. */
PyErr_BadInternalCall();
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