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From 0814467cc1b6a2839877277d3efa69cdd4582dd7 Mon Sep 17 00:00:00 2001
From: Richard Levitte <levitte@openssl.org>
Date: Fri, 20 Oct 2023 09:18:19 +0200
Subject: [PATCH] Make DH_check_pub_key() and DH_generate_key() safer yet
We already check for an excessively large P in DH_generate_key(), but not in
DH_check_pub_key(), and none of them check for an excessively large Q.
This change adds all the missing excessive size checks of P and Q.
It's to be noted that behaviours surrounding excessively sized P and Q
differ. DH_check() raises an error on the excessively sized P, but only
sets a flag for the excessively sized Q. This behaviour is mimicked in
DH_check_pub_key().
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22518)
(cherry picked from commit ddeb4b6c6d527e54ce9a99cba785c0f7776e54b6)
Backported-by: Clemens Lang <cllang@redhat.com>
---
crypto/dh/dh_check.c | 17 +++++++++++++++++
crypto/dh/dh_err.c | 1 +
crypto/dh/dh_key.c | 10 ++++++++++
crypto/err/openssl.txt | 1 +
include/openssl/dh.h | 6 ++++--
include/openssl/dherr.h | 1 +
6 files changed, 34 insertions(+), 2 deletions(-)
diff --git a/crypto/dh/dh_check.c b/crypto/dh/dh_check.c
index ae1b03bc92..424a3bb4cd 100644
--- a/crypto/dh/dh_check.c
+++ b/crypto/dh/dh_check.c
@@ -198,10 +198,27 @@ int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)
BN_CTX *ctx = NULL;
*ret = 0;
+
ctx = BN_CTX_new();
if (ctx == NULL)
goto err;
BN_CTX_start(ctx);
+
+ /* Don't do any checks at all with an excessively large modulus */
+ if (BN_num_bits(dh->p) > OPENSSL_DH_CHECK_MAX_MODULUS_BITS) {
+ DHerr(DH_F_DH_CHECK, DH_R_MODULUS_TOO_LARGE);
+ *ret = DH_MODULUS_TOO_LARGE | DH_CHECK_PUBKEY_INVALID;
+ goto err;
+ }
+ if (dh->q != NULL && BN_ucmp(dh->p, dh->q) < 0) {
+ *ret |= DH_CHECK_INVALID_Q_VALUE | DH_CHECK_PUBKEY_INVALID;
+ /* This may look strange here, but returning 1 after setting ret is
+ * correct. See also the behavior of the pub_key^q == 1 mod p check
+ * further down, which behaves in the same way. */
+ ok = 1;
+ goto err;
+ }
+
tmp = BN_CTX_get(ctx);
if (tmp == NULL || !BN_set_word(tmp, 1))
goto err;
diff --git a/crypto/dh/dh_err.c b/crypto/dh/dh_err.c
index 92800d3fcc..b3b1e7a706 100644
--- a/crypto/dh/dh_err.c
+++ b/crypto/dh/dh_err.c
@@ -87,6 +87,7 @@ static const ERR_STRING_DATA DH_str_reasons[] = {
{ERR_PACK(ERR_LIB_DH, 0, DH_R_PARAMETER_ENCODING_ERROR),
"parameter encoding error"},
{ERR_PACK(ERR_LIB_DH, 0, DH_R_PEER_KEY_ERROR), "peer key error"},
+ {ERR_PACK(ERR_LIB_DH, 0, DH_R_Q_TOO_LARGE), "q too large"},
{ERR_PACK(ERR_LIB_DH, 0, DH_R_SHARED_INFO_ERROR), "shared info error"},
{ERR_PACK(ERR_LIB_DH, 0, DH_R_UNABLE_TO_CHECK_GENERATOR),
"unable to check generator"},
diff --git a/crypto/dh/dh_key.c b/crypto/dh/dh_key.c
index 117f2fa883..9f5e6f6d4c 100644
--- a/crypto/dh/dh_key.c
+++ b/crypto/dh/dh_key.c
@@ -140,6 +140,11 @@ static int generate_key(DH *dh)
return 0;
}
+ if (dh->q != NULL && BN_num_bits(dh->q) > OPENSSL_DH_MAX_MODULUS_BITS) {
+ DHerr(DH_F_GENERATE_KEY, DH_R_Q_TOO_LARGE);
+ return 0;
+ }
+
ctx = BN_CTX_new();
if (ctx == NULL)
goto err;
@@ -250,6 +255,12 @@ static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
goto err;
}
+
+ if (dh->q != NULL && BN_num_bits(dh->q) > OPENSSL_DH_MAX_MODULUS_BITS) {
+ DHerr(DH_F_COMPUTE_KEY, DH_R_Q_TOO_LARGE);
+ goto err;
+ }
+
#ifdef OPENSSL_FIPS
if (FIPS_mode()
&& (BN_num_bits(dh->p) < OPENSSL_DH_FIPS_MIN_MODULUS_BITS)) {
diff --git a/crypto/err/openssl.txt b/crypto/err/openssl.txt
index c0a3cd720b..5e0ff47516 100644
--- a/crypto/err/openssl.txt
+++ b/crypto/err/openssl.txt
@@ -2151,6 +2151,7 @@DH_R_NO_PARAMETERS_SET:107:no parameters set
DH_R_NO_PRIVATE_VALUE:100:no private value
DH_R_PARAMETER_ENCODING_ERROR:105:parameter encoding error
DH_R_PEER_KEY_ERROR:111:peer key error
+DH_R_Q_TOO_LARGE:130:q too large
DH_R_SHARED_INFO_ERROR:113:shared info error
DH_R_UNABLE_TO_CHECK_GENERATOR:121:unable to check generator
DSA_R_BAD_Q_VALUE:102:bad q value
diff --git a/include/openssl/dh.h b/include/openssl/dh.h
index 6c6ff3636a..b7df43b44f 100644
--- a/include/openssl/dh.h
+++ b/include/openssl/dh.h
@@ -72,14 +72,16 @@ DECLARE_ASN1_ITEM(DHparams)
/* #define DH_GENERATOR_3 3 */
# define DH_GENERATOR_5 5
-/* DH_check error codes */
+/* DH_check error codes, some of them shared with DH_check_pub_key */
# define DH_CHECK_P_NOT_PRIME 0x01
# define DH_CHECK_P_NOT_SAFE_PRIME 0x02
# define DH_UNABLE_TO_CHECK_GENERATOR 0x04
# define DH_NOT_SUITABLE_GENERATOR 0x08
# define DH_CHECK_Q_NOT_PRIME 0x10
-# define DH_CHECK_INVALID_Q_VALUE 0x20
+# define DH_CHECK_INVALID_Q_VALUE 0x20 /* +DH_check_pub_key */
# define DH_CHECK_INVALID_J_VALUE 0x40
+/* DH_MODULUS_TOO_SMALL is 0x80 upstream */
+# define DH_MODULUS_TOO_LARGE 0x100 /* +DH_check_pub_key */
/* DH_check_pub_key error codes */
# define DH_CHECK_PUBKEY_TOO_SMALL 0x01
diff --git a/include/openssl/dherr.h b/include/openssl/dherr.h
index 528c819856..d66c35aa8e 100644
--- a/include/openssl/dherr.h
+++ b/include/openssl/dherr.h
@@ -87,6 +87,7 @@ int ERR_load_DH_strings(void);
# define DH_R_NON_FIPS_METHOD 202
# define DH_R_PARAMETER_ENCODING_ERROR 105
# define DH_R_PEER_KEY_ERROR 111
+# define DH_R_Q_TOO_LARGE 130
# define DH_R_SHARED_INFO_ERROR 113
# define DH_R_UNABLE_TO_CHECK_GENERATOR 121
--
2.41.0
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