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Forbid \C in UTF-8 patterns #21139

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Forbid \C in UTF-8 patterns #21139

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8 changes: 7 additions & 1 deletion ext/pcre/php_pcre.c
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Original file line number Diff line number Diff line change
Expand Up @@ -734,6 +734,8 @@ PHPAPI pcre_cache_entry* pcre_get_compiled_regex_cache_ex(zend_string *regex, bo
#ifdef PCRE2_UCP
coptions |= PCRE2_UCP;
#endif
/* The \C escape sequence is unsafe in PCRE2_UTF mode */
coptions |= PCRE2_NEVER_BACKSLASH_C;
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@devnexen devnexen Feb 5, 2026 •
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would need to document it somehow (UPGRADING ?) wdyt ?

break;
case 'J': coptions |= PCRE2_DUPNAMES; break;

Expand Down Expand Up @@ -787,7 +789,11 @@ PHPAPI pcre_cache_entry* pcre_get_compiled_regex_cache_ex(zend_string *regex, bo
if (key != regex) {
zend_string_release_ex(key, 0);
}
pcre2_get_error_message(errnumber, error, sizeof(error));
if (errnumber == PCRE2_ERROR_BACKSLASH_C_CALLER_DISABLED) {
strlcpy((char*)error, "using \\C is incompatible with the 'u' modifier", sizeof(error));
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@devnexen devnexen Feb 5, 2026

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yes the default message is a bit vague in this context, makes sense.

} else {
pcre2_get_error_message(errnumber, error, sizeof(error));
}
php_error_docref(NULL,E_WARNING, "Compilation failed: %s at offset %zu", error, erroffset);
Comment on lines +792 to 797
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@ndossche ndossche Feb 5, 2026

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I think the strlcpy call is ugly, but I won't object. Why not smth like this (and possibly rename error to error_buf):

Suggested change
if (errnumber == PCRE2_ERROR_BACKSLASH_C_CALLER_DISABLED) {
strlcpy((char*)error, "using \\C is incompatible with the 'u' modifier", sizeof(error));
} else {
pcre2_get_error_message(errnumber, error, sizeof(error));
}
php_error_docref(NULL,E_WARNING, "Compilation failed: %s at offset %zu", error, erroffset);
const char *err_msg = (const char *) error;
if (errnumber == PCRE2_ERROR_BACKSLASH_C_CALLER_DISABLED) {
err_msg = "using \\C is incompatible with the 'u' modifier";
} else {
pcre2_get_error_message(errnumber, error, sizeof(error));
}
php_error_docref(NULL,E_WARNING, "Compilation failed: %s at offset %zu", err_msg, erroffset);

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@devnexen devnexen Feb 6, 2026

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on that, I was surprised to see pcre2 provides a strcpy-like only for their own buffer type.

pcre_handle_exec_error(PCRE2_ERROR_INTERNAL);
efree(pattern);
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15 changes: 15 additions & 0 deletions ext/pcre/tests/gh21134.phpt
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@@ -0,0 +1,15 @@
--TEST--
GH-21134: ASan negative-size-param in preg_match_all() with \C + UTF-8 multibyte input
--CREDITS--
vi3tL0u1s
--FILE--
<?php

$r = preg_match_all("/(.*)\\C/u", "à", $m);
var_dump($r, $m);

?>
--EXPECTF--
Warning: preg_match_all(): Compilation failed: using \C is incompatible with the 'u' modifier at offset 6 in %s on line %d
bool(false)
NULL
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