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Fix GH-16501: gmp_random_bits overflow. #16503

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Fix GH-16501: gmp_random_bits overflow. #16503

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ec3ccb5
Fix GH-16501: gmp_random_bits overflow.
devnexen Oct 19, 2024
fa54bc4
fix existing test
devnexen Oct 19, 2024
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12 changes: 9 additions & 3 deletions ext/gmp/gmp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1803,15 +1803,21 @@ ZEND_FUNCTION(gmp_random_bits)
RETURN_THROWS();
}

if (bits <= 0) {
zend_argument_value_error(1, "must be greater than or equal to 1");
#if SIZEOF_SIZE_T == 4
const zend_long maxbits = ULONG_MAX / GMP_NUMB_BITS;
#else
const zend_long maxbits = INT_MAX;
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This still can overflow. libgmp does this check, but afterwards calculates ((new_alloc) * sizeof (mp_limb_t)), where sizeof(mp_limb_t) is certainly larger than 2 (I assume it's usually four or eight).

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Disregard. This is fine; I was confused by 32bit using ULONG_MAX, but 64bit using INT_MAX. The 32bit case looks fishy (for LP64), though.

#endif

if (bits <= 0 || bits > maxbits) {
zend_argument_value_error(1, "must be between 1 and " ZEND_LONG_FMT, maxbits);
RETURN_THROWS();
}

INIT_GMP_RETVAL(gmpnum_result);
gmp_init_random();

mpz_urandomb(gmpnum_result, GMPG(rand_state), bits);
mpz_urandomb(gmpnum_result, GMPG(rand_state), (mp_bitcnt_t)bits);
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Is the mp_bitcnt_t cast correct?

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It s just to avoid pedantic build warning I guess, bits being always > 0 and < max value for unsigned long int ; I think it is fine.

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Well, just extraneous; I'd remove it (could still trigger some compiler/analyser diagnostic without the cast).

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Ah, I overlooked your comment. Let's leave it as is.

}
/* }}} */

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14 changes: 14 additions & 0 deletions ext/gmp/tests/gh16501.phpt
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@@ -0,0 +1,14 @@
--TEST--
GH-16501 (gmp_random_bits overflow)
--EXTENSIONS--
gmp
--FILE--
<?php
try {
gmp_random_bits(PHP_INT_MAX);
} catch (\ValueError $e) {
echo $e->getMessage();
}
?>
--EXPECTF--
gmp_random_bits(): Argument #1 ($bits) must be between 1 and %d
6 changes: 3 additions & 3 deletions ext/gmp/tests/gmp_random_bits.phpt
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Expand Up @@ -40,7 +40,7 @@ while (1) {

echo "Done\n";
?>
--EXPECT--
gmp_random_bits(): Argument #1 ($bits) must be greater than or equal to 1
gmp_random_bits(): Argument #1 ($bits) must be greater than or equal to 1
--EXPECTF--
gmp_random_bits(): Argument #1 ($bits) must be between 1 and %d
gmp_random_bits(): Argument #1 ($bits) must be between 1 and %d
Done
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