From 9002fd07327a91f35ba6c1307e71fa6fd4409b7f Mon Sep 17 00:00:00 2001
From: Tomas Mraz <tomas@openssl.org>
Date: Tue, 25 Jul 2023 15:22:48 +0200
Subject: [PATCH] DH_check(): Do not try checking q properties if it is
 obviously invalid

If  |q| >= |p| then the q value is obviously wrong as q
is supposed to be a prime divisor of p-1.

We check if p is overly large so this added test implies that
q is not large either when performing subsequent tests using that
q value.

Otherwise if it is too large these additional checks of the q value
such as the primality test can then trigger DoS by doing overly long
computations.

Fixes CVE-2023-3817

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/21550)

(cherry picked from commit 1c16253f3c3a8d1e25918c3f404aae6a5b0893de)
(cherry picked from commit 6a1eb62c29db6cb5eec707f9338aee00f44e26f5)
---
 crypto/dh/dh_check.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/crypto/dh/dh_check.c b/crypto/dh/dh_check.c
index aef6f9b1b7..fbe2797569 100644
--- a/crypto/dh/dh_check.c
+++ b/crypto/dh/dh_check.c
@@ -143,7 +143,7 @@ int DH_check(const DH *dh, int *ret)
 #ifdef FIPS_MODULE
     return DH_check_params(dh, ret);
 #else
-    int ok = 0, r;
+    int ok = 0, r, q_good = 0;
     BN_CTX *ctx = NULL;
     BIGNUM *t1 = NULL, *t2 = NULL;
     int nid = DH_get_nid((DH *)dh);
@@ -172,6 +172,13 @@ int DH_check(const DH *dh, int *ret)
         goto err;
 
     if (dh->params.q != NULL) {
+        if (BN_ucmp(dh->params.p, dh->params.q) > 0)
+            q_good = 1;
+        else
+            *ret |= DH_CHECK_INVALID_Q_VALUE;
+    }
+
+    if (q_good) {
         if (BN_cmp(dh->params.g, BN_value_one()) <= 0)
             *ret |= DH_NOT_SUITABLE_GENERATOR;
         else if (BN_cmp(dh->params.g, dh->params.p) >= 0)
-- 
2.27.0