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Fix GH-16878: Prevent overflow in gmp_fact() for large GMP inputs (ext/gmp) #20900

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Fix GH-16878: Prevent overflow in gmp_fact() for large GMP inputs (ext/gmp) #20900

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e053c6b
ext/gmp: Reject too-large inputs in gmp_fact() to avoid overflow
khaledalam Jan 10, 2026
cf8d259
Merge remote-tracking branch 'origin' into fix-gh16878-gmp-fact-overflow
khaledalam Jan 10, 2026
8d8a8bd
feat: remove unrelated changes.
khaledalam Jan 10, 2026
1af8acd
test: fix gmp_fact test case on x32.
khaledalam Jan 10, 2026
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7 changes: 5 additions & 2 deletions ext/gmp/gmp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1094,8 +1094,11 @@ ZEND_FUNCTION(gmp_fact)
RETURN_THROWS();
}

// TODO: Check that we don't an int that is larger than an unsigned long?
// Could use mpz_fits_slong_p() if we revert to using mpz_get_si()
/* mpz_fac_ui() takes an unsigned long; avoid truncation/overflow + huge work */
if (!mpz_fits_ulong_p(gmpnum) || mpz_cmp_ui(gmpnum, 100000) > 0) {
zend_argument_value_error(1, "is too large");
RETURN_THROWS();
}

INIT_GMP_RETVAL(gmpnum_result);
mpz_fac_ui(gmpnum_result, mpz_get_ui(gmpnum));
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58 changes: 58 additions & 0 deletions ext/gmp/tests/gh16878.phpt
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@@ -0,0 +1,58 @@
--TEST--
GH-16878: Core dump when gmp_fact allocates huge memory
--EXTENSIONS--
gmp
--FILE--
<?php
echo "Test 1: Factorial of 2^50 + 1\n";
try {
$value = gmp_add(gmp_pow(2, 50), 1);
echo "Calculating factorial of: ", gmp_strval($value), "\n";
$result = gmp_fact($value);
echo "Result: " . gmp_strval($result) . "\n";
} catch (\ValueError $e) {
echo "ValueError: " . $e->getMessage() . "\n";
} catch (\Error $e) {
echo "Error: " . $e->getMessage() . "\n";
}

echo "\nTest 2: Another large value\n";
try {
$value = gmp_init('1000000000000'); // 1 trillion
echo "Calculating factorial of: ", gmp_strval($value), "\n";
$result = gmp_fact($value);
echo "Result: " . gmp_strval($result) . "\n";
} catch (\ValueError $e) {
echo "ValueError: " . $e->getMessage() . "\n";
} catch (\Error $e) {
echo "Error: " . $e->getMessage() . "\n";
}

echo "\nTest 3: Moderately large value that should work\n";
try {
$value = 100;
echo "Calculating factorial of: $value\n";
$result = gmp_fact($value);
echo "Result length: " . strlen(gmp_strval($result)) . " digits\n";
} catch (\ValueError $e) {
echo "ValueError: " . $e->getMessage() . "\n";
} catch (\Error $e) {
echo "Error: " . $e->getMessage() . "\n";
}

echo "\nDone\n";
?>
--EXPECTF--
Test 1: Factorial of 2^50 + 1
Calculating factorial of: 1125899906842625
ValueError: %s

Test 2: Another large value
Calculating factorial of: 1000000000000
ValueError: %s

Test 3: Moderately large value that should work
Calculating factorial of: 100
Result length: 158 digits

Done
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