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Fix GH-16870: gmp_pow(64, 11) throws overflow exception #16884

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Fix GH-16870: gmp_pow(64, 11) throws overflow exception #16884

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d5ed93b
Fix GH-16870: gmp_pow(64, 11) throws overflow exception
cmb69 Nov 21, 2024
4acc1b2
Remove now unused variable
cmb69 Nov 21, 2024
9ce9a4e
Count bits instead of bytes
cmb69 Nov 24, 2024
333524e
Use `mpz_sizeinbase(gmpnum_base, 2) - 1`
cmb69 Nov 25, 2024
3998435
More thorough testing
cmb69 Nov 25, 2024
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8 changes: 3 additions & 5 deletions ext/gmp/gmp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1350,22 +1350,20 @@ ZEND_FUNCTION(gmp_pow)
RETURN_THROWS();
}

double powmax = log((double)ZEND_LONG_MAX);
double max_bits = 16000; // TODO: value is very small, but passed current test suite
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max_bits is a misnomer now; it's actually something like max_double_bits. Maybe someone has an idea for a good name. Alternatively, we could double the value here, and check against > max_bits / 2.0 below. Shouldn't be a performance issue, if we declare const or use a macro.


if (Z_TYPE_P(base_arg) == IS_LONG && Z_LVAL_P(base_arg) >= 0) {
INIT_GMP_RETVAL(gmpnum_result);
if ((log(Z_LVAL_P(base_arg)) * exp) > powmax) {
if ((log2(Z_LVAL_P(base_arg)) * exp) > max_bits) {
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For parity with the else branch, this should be

Suggested change
if ((log2(Z_LVAL_P(base_arg)) * exp) > max_bits) {
if ((floor(log2(Z_LVAL_P(base_arg))) * exp) > max_bits) {

But that would fail the last check in gmp_pow_fpe.phpt.

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);
gmpnum = mpz_get_ui(gmpnum_base);
if ((log(gmpnum) * exp) > powmax) {
if (((mpz_sizeinbase(gmpnum_base, 2) - 1) * exp) > max_bits) {
FREE_GMP_TEMP(temp_base);
zend_value_error("base and exponent overflow");
RETURN_THROWS();
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44 changes: 44 additions & 0 deletions ext/gmp/tests/gh16870.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
--TEST--
GH-16870 (gmp_pow(64, 11) throws overflow exception)
--EXTENSIONS--
gmp
--FILE--
<?php
var_dump((string) gmp_pow(64, 11));
var_dump((string) gmp_pow(-1, PHP_INT_MAX));
var_dump((string) gmp_pow(0, PHP_INT_MAX));
var_dump((string) gmp_pow(1, PHP_INT_MAX));
var_dump((string) gmp_pow("-1", PHP_INT_MAX));
var_dump((string) gmp_pow("0", PHP_INT_MAX));
var_dump((string) gmp_pow("1", PHP_INT_MAX));
var_dump((string) gmp_pow(3, 10094));
Comment on lines +7 to +14
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Please add tests that use the ** operator, as those would also be affected I guess? Or did we somehow not covered this in the initial bug fix?

try {
var_dump((string) gmp_pow(3, 10095));
} catch (ValueError $e) {
echo $e->getMessage(), "\n";
}
var_dump((string) gmp_pow("3", 16000));
try {
var_dump((string) gmp_pow("3", 16001));
} catch (ValueError $e) {
echo $e->getMessage(), "\n";
}
try {
gmp_pow("18446744073709551616", 0x7fffffff);
} catch (ValueError $e) {
echo $e->getMessage(), "\n";
}
?>
--EXPECT--
string(20) "73786976294838206464"
string(2) "-1"
string(1) "0"
string(1) "1"
string(2) "-1"
string(1) "0"
string(1) "1"
string(4817) "11533075637415496487592281331871174224637747280976783291049637915717488227409677235589985655833465069923970899504086533698509270485890415334138939234858553150826813059505821259421456502508459186875462194341065386126027027801534249219977601579402736284286658193223986383464522124431223004297979465911201782466728745878641327908224534851121272255882547583191118693484780082125687029148743930859469820619678076958478118783489386874938191595509014766881676382421423016318326239973711548512612598309512106273519481784053091183020220527884557279099056661262994370342893384956309190106859775380860788112440147017820801636914712819201261397772886095769514880661889558718248848498944978298184551864073632680231658424104129061352234739458896093955810573478729324201585738500508329505836621196751694435138391020244524002159614497981053936222615557057893320016368675928259661493908333929142877007002885770583505582564736312299864984293531873864785061265017587679806566346937678293678998816923947602772262547079648068153366270700158042945319861666957554360301554853013633335061966660135604818152043268703879168177293143076972823669959649421742685351867333233375304163232177777149647584860455637044208414453159294097804572134602265717132591722340206521295262152747278343230909914146841030285355493512813207869020568988470431918854802958290677478180815612525670586383633573558530284054578826178408362217876241833460468595240122498437860045968972498437913593528141080036063648369793150134377980502301181887963885053064585044647683192966091405359713319504738027316338262877696465232479348268959047133196943904242825585164714190795727177289193707936288448757607620884395915808810169838006401939994129380221798621603922122120110978533508520737364952338800186754919489090671539065182388363071753440332332249991931441542792540505050771825563716012931675348704705770151623950861159540884480458342871213236644751652034678244538551634573645445081249713336054306352098643138437770637045046645088903473177825834711859735016452422236013031965468217796705403248576918867778077692445192471434260249043920105606081135347705471262201478880521919759088254915924663179252552339836393647820778888239706561457303926528584995539088709710358964191141263305063547111178725937342302098044093057127459931531969143049596597192023941133832945605615334970253334228000275114412032554739404197725782911039011770988887590764320264786241103943964745418928079629108956619786453969570711590050691932385791267203614515551830325273413306776447458839519881809227379691968602616006998938263546188046854314963767036370641280548468755684510584427490525867039168065160950239341183895809995044275414602304583704717163464266405807330989661792426013150352392087304879788737912048852459292593719156210711473037637547103646633898687511717796971016064790324828663563087681469449755567209995580910951033394998762663853063178438599205534963057781410172898489892718908461868307071054446450561922351101300171637091591413816045421511530390792520180437209031104189440498889042828323443697952275508957192579916808786021116553372668204960814067368778487925938948510853284619996784341333402905801347256105023014742400298085781418992355245244156505542455222650319803872472017206844050437780143120498808268520589669594027795801438407544679315677995610024554202130961041463899262204300934333414826431857761050231879979281031546519214077200265877969102451689679880205621377656924576256346866648855273620211964454200666629878075419597919852822938780309508644306537653750021962025990643059595796196697895840873603111986834333194711636636348263344926116699951769640079227690346397831461531292290830418182071541604993899466537843235494262980341932336568387592159813596163181944639955690022622519454338194071345149482727629363247164883011183345428351495527322131091146630729105930006087949486403591684325160001638574604024394536745386047627900917257815847545171976792043319150875518285604781055959205372582776540005233644057612223824800964132529686684541425442628267789238706523810350415794716578754447768048781908772346231178543166514429377036603488773915367383002286671376468419724428841687176592794065754546867062875406331140604798929779064101927739181639627468245954232039869046707424467620707677501544195000789093397664181696452971158542902981581987839614407777681067561791112963614073029383140487183899555545496926164982886373099319907733644729223215119356475099918343507159953339661877757192384854128503625650657367508508660932110689248806971912244789249729377746967911203753323354211795666229306826885533076923224636360742503247191795910899694603683976297608514851769022529820637273260270472582103791801328333797745859172743767108242081619361527230269139392742585955692131235200252584005651254346885442923058733606248191257109473881785843652930393562387120056434695224498865819867705157369"
base and exponent overflow
string(7634) 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base and exponent overflow
base and exponent overflow
2 changes: 1 addition & 1 deletion ext/gmp/tests/gmp_pow_fpe.phpt
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@ try {
echo $e->getMessage() . PHP_EOL;
}
try {
gmp_pow(gmp_init(PHP_INT_MAX), 256);
gmp_pow(PHP_INT_MAX, 256);
} catch (\ValueError $e) {
echo $e->getMessage();
}
Expand Down
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