From 3118eb64934499d93db3230748a452351d1d9a65 Mon Sep 17 00:00:00 2001 From: Tomas Mraz Date: Mon, 28 Feb 2022 18:26:21 +0100 Subject: [PATCH] Fix possible infinite loop in BN_mod_sqrt() The calculation in some cases does not finish for non-prime p. This fixes CVE-2022-0778. Based on patch by David Benjamin . Reviewed-by: Paul Dale Reviewed-by: Matt Caswell --- crypto/bn/bn_sqrt.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) From b5fcb7e133725b8b2eb66f63f5142710ed63a6d1 Mon Sep 17 00:00:00 2001 From: Tomas Mraz Date: Mon, 28 Feb 2022 18:26:30 +0100 Subject: [PATCH] Add documentation of BN_mod_sqrt() Reviewed-by: Paul Dale Reviewed-by: Matt Caswell --- doc/man3/BN_add.pod | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) From 3ef5c3034e5c545f34d6929568f3f2b10ac4bdf0 Mon Sep 17 00:00:00 2001 From: Tomas Mraz Date: Mon, 28 Feb 2022 18:26:35 +0100 Subject: [PATCH] Add a negative testcase for BN_mod_sqrt Reviewed-by: Paul Dale Reviewed-by: Matt Caswell --- test/bntest.c | 11 ++++++++++- test/recipes/10-test_bn_data/bnmod.txt | 12 ++++++++++++ 2 files changed, 22 insertions(+), 1 deletion(-) diff --git a/crypto/bn/bn_sqrt.c b/crypto/bn/bn_sqrt.c index 1723d5ded5a8..53b0f559855c 100644 --- a/crypto/bn/bn_sqrt.c +++ b/crypto/bn/bn_sqrt.c @@ -14,7 +14,8 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx) /* * Returns 'ret' such that ret^2 == a (mod p), using the Tonelli/Shanks * algorithm (cf. Henri Cohen, "A Course in Algebraic Computational Number - * Theory", algorithm 1.5.1). 'p' must be prime! + * Theory", algorithm 1.5.1). 'p' must be prime, otherwise an error or + * an incorrect "result" will be returned. */ { BIGNUM *ret = in; @@ -301,18 +302,23 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx) goto vrfy; } - /* find smallest i such that b^(2^i) = 1 */ - i = 1; - if (!BN_mod_sqr(t, b, p, ctx)) - goto end; - while (!BN_is_one(t)) { - i++; - if (i == e) { - BNerr(BN_F_BN_MOD_SQRT, BN_R_NOT_A_SQUARE); - goto end; + /* Find the smallest i, 0 < i < e, such that b^(2^i) = 1. */ + for (i = 1; i < e; i++) { + if (i == 1) { + if (!BN_mod_sqr(t, b, p, ctx)) + goto end; + + } else { + if (!BN_mod_mul(t, t, t, p, ctx)) + goto end; } - if (!BN_mod_mul(t, t, t, p, ctx)) - goto end; + if (BN_is_one(t)) + break; + } + /* If not found, a is not a square or p is not prime. */ + if (i >= e) { + BNerr(BN_F_BN_MOD_SQRT, BN_R_NOT_A_SQUARE); + goto end; } /* t := y^2^(e - i - 1) */ diff --git a/doc/man3/BN_add.pod b/doc/man3/BN_add.pod index dccd4790ede7..1f5e37a4d183 100644 --- a/doc/man3/BN_add.pod +++ b/doc/man3/BN_add.pod @@ -3,7 +3,7 @@ =head1 NAME BN_add, BN_sub, BN_mul, BN_sqr, BN_div, BN_mod, BN_nnmod, BN_mod_add, -BN_mod_sub, BN_mod_mul, BN_mod_sqr, BN_exp, BN_mod_exp, BN_gcd - +BN_mod_sub, BN_mod_mul, BN_mod_sqr, BN_mod_sqrt, BN_exp, BN_mod_exp, BN_gcd - arithmetic operations on BIGNUMs =head1 SYNOPSIS @@ -36,6 +36,8 @@ arithmetic operations on BIGNUMs int BN_mod_sqr(BIGNUM *r, BIGNUM *a, const BIGNUM *m, BN_CTX *ctx); + BIGNUM *BN_mod_sqrt(BIGNUM *in, BIGNUM *a, const BIGNUM *p, BN_CTX *ctx); + int BN_exp(BIGNUM *r, BIGNUM *a, BIGNUM *p, BN_CTX *ctx); int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p, @@ -87,6 +89,12 @@ L. BN_mod_sqr() takes the square of I modulo B and places the result in I. +BN_mod_sqrt() returns the modular square root of I such that +C. The modulus I

must be a +prime, otherwise an error or an incorrect "result" will be returned. +The result is stored into I which can be NULL. The result will be +newly allocated in that case. + BN_exp() raises I to the I

-th power and places the result in I (C). This function is faster than repeated applications of BN_mul(). @@ -108,7 +116,10 @@ the arguments. =head1 RETURN VALUES -For all functions, 1 is returned for success, 0 on error. The return +The BN_mod_sqrt() returns the result (possibly incorrect if I

is +not a prime), or NULL. + +For all remaining functions, 1 is returned for success, 0 on error. The return value should always be checked (e.g., C). The error codes can be obtained by L. diff --git a/test/bntest.c b/test/bntest.c index 390dd800733e..1cab660bcafb 100644 --- a/test/bntest.c +++ b/test/bntest.c @@ -1729,8 +1729,17 @@ static int file_modsqrt(STANZA *s) || !TEST_ptr(ret2 = BN_new())) goto err; + if (BN_is_negative(mod_sqrt)) { + /* A negative testcase */ + if (!TEST_ptr_null(BN_mod_sqrt(ret, a, p, ctx))) + goto err; + + st = 1; + goto err; + } + /* There are two possible answers. */ - if (!TEST_true(BN_mod_sqrt(ret, a, p, ctx)) + if (!TEST_ptr(BN_mod_sqrt(ret, a, p, ctx)) || !TEST_true(BN_sub(ret2, p, ret))) goto err; diff --git a/test/recipes/10-test_bn_data/bnmod.txt b/test/recipes/10-test_bn_data/bnmod.txt index 5ea4d031f271..e28cc6bfb02e 100644 --- a/test/recipes/10-test_bn_data/bnmod.txt +++ b/test/recipes/10-test_bn_data/bnmod.txt @@ -2799,3 +2799,15 @@ P = 9df9d6cc20b8540411af4e5357ef2b0353cb1f2ab5ffc3e246b41c32f71e951f ModSqrt = a1d52989f12f204d3d2167d9b1e6c8a6174c0c786a979a5952383b7b8bd186 A = 2eee37cf06228a387788188e650bc6d8a2ff402931443f69156a29155eca07dcb45f3aac238d92943c0c25c896098716baa433f25bd696a142f5a69d5d937e81 P = 9df9d6cc20b8540411af4e5357ef2b0353cb1f2ab5ffc3e246b41c32f71e951f + +# Negative testcases for BN_mod_sqrt() + +# This one triggers an infinite loop with unfixed implementation +# It should just fail. +ModSqrt = -1 +A = 20a7ee +P = 460201 + +ModSqrt = -1 +A = 65bebdb00a96fc814ec44b81f98b59fba3c30203928fa5214c51e0a97091645280c947b005847f239758482b9bfc45b066fde340d1fe32fc9c1bf02e1b2d0ed +P = 9df9d6cc20b8540411af4e5357ef2b0353cb1f2ab5ffc3e246b41c32f71e951f