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From 2c0f7d46b8449423446cfe1e52fc1e1ecd506b62 Mon Sep 17 00:00:00 2001
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From: Tomas Mraz <tomas@openssl.org>
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Date: Wed, 2 Feb 2022 17:47:26 +0100
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Subject: [PATCH] Replace size check with more meaningful pubkey check
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It does not make sense to check the size because this
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function can be used in other contexts than in TLS-1.3 and
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the value might not be padded to the size of p.
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However it makes sense to do the partial pubkey check because
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there is no valid reason having the pubkey value outside the
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1 < pubkey < p-1 bounds.
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Fixes #15465
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Reviewed-by: Paul Dale <pauli@openssl.org>
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(Merged from https://github.com/openssl/openssl/pull/17630)
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---
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crypto/dh/dh_key.c | 11 ++++-------
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1 file changed, 4 insertions(+), 7 deletions(-)
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diff --git a/crypto/dh/dh_key.c b/crypto/dh/dh_key.c
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index 6b8cd550f2..c78ed618bf 100644
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--- a/crypto/dh/dh_key.c
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+++ b/crypto/dh/dh_key.c
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@@ -375,20 +375,17 @@ int ossl_dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
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int err_reason = DH_R_BN_ERROR;
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BIGNUM *pubkey = NULL;
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const BIGNUM *p;
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- size_t p_size;
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+ int ret;
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if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
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goto err;
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DH_get0_pqg(dh, &p, NULL, NULL);
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- if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
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+ if (p == NULL || BN_num_bytes(p) == 0) {
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err_reason = DH_R_NO_PARAMETERS_SET;
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goto err;
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}
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- /*
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- * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
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- * public key is of size not equal to size of p
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- */
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- if (BN_is_zero(pubkey) || p_size != len) {
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+ /* Prevent small subgroup attacks per RFC 8446 Section 4.2.8.1 */
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+ if (!ossl_dh_check_pub_key_partial(dh, pubkey, &ret)) {
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err_reason = DH_R_INVALID_PUBKEY;
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goto err;
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}
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--
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2.35.1
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