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ext/gmp: gmp_pow fix FPE with large values. #16384

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ext/gmp: gmp_pow fix FPE with large values. #16384

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0c04ae6
ext/gmp: gmp_pow fix FPE with large values.
devnexen Oct 12, 2024
e2b07d7
add test
devnexen Oct 12, 2024
3534f0a
add tests
devnexen Oct 21, 2024
72b5653
change comparison limit, now new tests overflow on 64 bits.
devnexen Oct 24, 2024
7f432a1
zend_ulong
devnexen Oct 25, 2024
752627d
fix tests on 32 bits attempt.
devnexen Oct 25, 2024
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38 changes: 13 additions & 25 deletions ext/gmp/gmp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1282,39 +1282,27 @@ ZEND_FUNCTION(gmp_pow)
RETURN_THROWS();
}

double powmax = log((double)ZEND_LONG_MAX);

if (Z_TYPE_P(base_arg) == IS_LONG && Z_LVAL_P(base_arg) >= 0) {
INIT_GMP_RETVAL(gmpnum_result);
if (exp >= INT_MAX) {
mpz_t base_num, exp_num, mod;
mpz_init(base_num);
mpz_init(exp_num);
mpz_init(mod);
mpz_set_si(base_num, Z_LVAL_P(base_arg));
mpz_set_si(exp_num, exp);
mpz_set_ui(mod, UINT_MAX);
mpz_powm(gmpnum_result, base_num, exp_num, mod);
mpz_clear(mod);
mpz_clear(exp_num);
mpz_clear(base_num);
} else {
mpz_ui_pow_ui(gmpnum_result, Z_LVAL_P(base_arg), exp);
if ((log(Z_LVAL_P(base_arg)) * exp) > powmax) {
zend_value_error("base and exponent overflow");
RETURN_THROWS();
}
mpz_ui_pow_ui(gmpnum_result, Z_LVAL_P(base_arg), exp);
} else {
mpz_ptr gmpnum_base;
zend_ulong gmpnum;
FETCH_GMP_ZVAL(gmpnum_base, base_arg, temp_base, 1);
INIT_GMP_RETVAL(gmpnum_result);
if (exp >= INT_MAX) {
mpz_t exp_num, mod;
mpz_init(exp_num);
mpz_init(mod);
mpz_set_si(exp_num, exp);
mpz_set_ui(mod, UINT_MAX);
mpz_powm(gmpnum_result, gmpnum_base, exp_num, mod);
mpz_clear(mod);
mpz_clear(exp_num);
} else {
mpz_pow_ui(gmpnum_result, gmpnum_base, exp);
gmpnum = mpz_get_ui(gmpnum_base);
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This can overflow; e.g. gmp_pow(gmp_init(PHP_INT_MAX), 256) is sufficient for overflow on x64 Windows; on LP64, gmp_pow(gmp_add(gmp_mul(gmp_init(PHP_INT_MAX), gmp_init(PHP_INT_MAX)), 3), 256) is likely to overflow here.

It seems to me that the libgmp/mpir developers where so focused to make it fast, that they forgot to make it right.

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I ll add those two cases, the latter does not crash on linux/64 locally.

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The problem is that mpz_get_ui() returns unsigned long long int (at least on Windows) which is an unsigned 64bit value. If you assign that to an unsigned long, the value will be truncated (well-defined behavior, but likely not desired here). It might be better to declare mpir_ui gmpnum, and then go from there, but that might cause further issues down the line.

if ((log(gmpnum) * exp) > powmax) {
FREE_GMP_TEMP(temp_base);
zend_value_error("base and exponent overflow");
RETURN_THROWS();
}
mpz_pow_ui(gmpnum_result, gmpnum_base, exp);
FREE_GMP_TEMP(temp_base);
}
}
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2 changes: 2 additions & 0 deletions ext/gmp/tests/gmp_pow.phpt
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Expand Up @@ -2,6 +2,8 @@
gmp_pow() basic tests
--EXTENSIONS--
gmp
--SKIPIF--
<?php if (PHP_INT_SIZE != 8) die("skip this test is for 64bit platform only"); ?>
--FILE--
<?php

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77 changes: 77 additions & 0 deletions ext/gmp/tests/gmp_pow_32bits.phpt
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@@ -0,0 +1,77 @@
--TEST--
gmp_pow() basic tests
--EXTENSIONS--
gmp
--SKIPIF--
<?php if (PHP_INT_SIZE != 4) die("skip this test is for 32bit platform only"); ?>
--FILE--
<?php

var_dump(gmp_strval(gmp_pow(2,10)));
var_dump(gmp_strval(gmp_pow(-2,10)));
var_dump(gmp_strval(gmp_pow(-2,11)));
var_dump(gmp_strval(gmp_pow("2",10)));
var_dump(gmp_strval(gmp_pow("2",0)));
try {
gmp_pow("2", -1);
} catch (ValueError $exception) {
echo $exception->getMessage() . "\n";
}
var_dump(gmp_strval(gmp_pow("-2",10)));
try {
gmp_pow(20,10);
} catch (ValueError $exception) {
echo $exception->getMessage() . "\n";
}
try {
gmp_pow(50,10);
} catch (ValueError $exception) {
echo $exception->getMessage() . "\n";
}
try {
gmp_pow(50,-5);
} catch (ValueError $exception) {
echo $exception->getMessage() . "\n";
}
try {
$n = gmp_init("20");
gmp_pow($n,10);
} catch (ValueError $exception) {
echo $exception->getMessage() . "\n";
}
try {
$n = gmp_init("-20");
gmp_pow($n,10);
} catch (ValueError $exception) {
echo $exception->getMessage() . "\n";
}
try {
var_dump(gmp_pow(2,array()));
} catch (TypeError $e) {
echo $e->getMessage(), "\n";
}

try {
var_dump(gmp_pow(array(),10));
} catch (\TypeError $e) {
echo $e->getMessage() . \PHP_EOL;
}

echo "Done\n";
?>
--EXPECT--
string(4) "1024"
string(4) "1024"
string(5) "-2048"
string(4) "1024"
string(1) "1"
gmp_pow(): Argument #2 ($exponent) must be greater than or equal to 0
string(4) "1024"
base and exponent overflow
base and exponent overflow
gmp_pow(): Argument #2 ($exponent) must be greater than or equal to 0
base and exponent overflow
base and exponent overflow
gmp_pow(): Argument #2 ($exponent) must be of type int, array given
gmp_pow(): Argument #1 ($num) must be of type GMP|string|int, array given
Done
35 changes: 25 additions & 10 deletions ext/gmp/tests/gmp_pow_fpe.phpt
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Expand Up @@ -6,15 +6,30 @@ gmp
<?php
$g = gmp_init(256);

var_dump(gmp_pow($g, PHP_INT_MAX));
var_dump(gmp_pow(256, PHP_INT_MAX));
?>
--EXPECTF--
object(GMP)#2 (1) {
["num"]=>
string(%d) "%s"
try {
gmp_pow($g, PHP_INT_MAX);
} catch (\ValueError $e) {
echo $e->getMessage() . PHP_EOL;
}
object(GMP)#2 (1) {
["num"]=>
string(%d) "%s"
try {
gmp_pow(256, PHP_INT_MAX);
} catch (\ValueError $e) {
echo $e->getMessage() . PHP_EOL;
}

try {
gmp_pow(gmp_add(gmp_mul(gmp_init(PHP_INT_MAX), gmp_init(PHP_INT_MAX)), 3), 256);
} catch (\ValueError $e) {
echo $e->getMessage() . PHP_EOL;
}
try {
gmp_pow(gmp_init(PHP_INT_MAX), 256);
} catch (\ValueError $e) {
echo $e->getMessage();
}
?>
--EXPECTF--
base and exponent overflow
base and exponent overflow
base and exponent overflow
base and exponent overflow
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