diff options
| author | Tomas Mraz <tomas@openssl.org> | 2022-02-28 18:26:21 +0100 |
|---|---|---|
| committer | Matt Caswell <matt@openssl.org> | 2022-03-15 14:15:12 +0100 |
| commit | 9eafb53614bf65797db25f467946e735e1b43dc9 (patch) | |
| tree | 3b3262d7c346c484e33fbd946bf33b6e4ffc7692 /crypto/bn | |
| parent | Fix signed integer overflow in evp_enc (diff) | |
| download | openssl-9eafb53614bf65797db25f467946e735e1b43dc9.tar.xz openssl-9eafb53614bf65797db25f467946e735e1b43dc9.zip | |
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 <davidben@google.com>.
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Diffstat (limited to 'crypto/bn')
| -rw-r--r-- | crypto/bn/bn_sqrt.c | 30 |
1 files changed, 18 insertions, 12 deletions
diff --git a/crypto/bn/bn_sqrt.c b/crypto/bn/bn_sqrt.c index b663ae5ec5..c5ea7ab194 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; @@ -303,18 +304,23 @@ 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) { - ERR_raise(ERR_LIB_BN, 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) { + ERR_raise(ERR_LIB_BN, BN_R_NOT_A_SQUARE); + goto end; } /* t := y^2^(e - i - 1) */ |