From f470b130139919f32926b3f5a75ba4d161cbcf88 Mon Sep 17 00:00:00 2001
From: Clemens Lang <[email protected]>
Date: Tue, 1 Mar 2022 15:44:18 +0100
Subject: [PATCH 2/2] Allow SHA1 in seclevel 1 if rh-allow-sha1-signatures =
 yes

NOTE: This patch is ported from CentOS 9 / RHEL 9, where it allows SHA1
in seclevel 2 if rh-allow-sha1-signatures = yes. This was chosen because
on CentOS 9 and RHEL 9, the LEGACY crypto policy sets the security level
to 2.

On Fedora 35 (with OpenSSL 1.1) the legacy crypto policy uses security
level 1. Because Fedora 36 supports both OpenSSL 1.1 and OpenSSL 3, and
we want the legacy crypto policy to allow SHA-1 in TLS, the only option
to make this happen consistently in both OpenSSL 1.1 and OpenSSL 3 is
SECLEVEL=1 (which will allow SHA-1 in OpenSSL 1.1) and this change to
allow SHA-1 in SECLEVEL=1 with rh-allow-sha1-signatures = yes (which
will allow SHA-1 in OpenSSL 3).

The change from CentOS 9 / RHEL 9 cannot be applied unmodified, because
rh-allow-sha1-signatures will default to yes in Fedora (according to our
current plans including until F38), and the security level in the
DEFAULT crypto policy is 2, i.e., the unmodified change would weaken the
default configuration.

Related: rhbz#2055796
Related: rhbz#2070977
---
 crypto/x509/x509_vfy.c        | 20 ++++++++++-
 doc/man5/config.pod           |  7 ++++
 ssl/t1_lib.c                  | 67 ++++++++++++++++++++++++++++-------
 test/recipes/25-test_verify.t |  4 +--
 4 files changed, 82 insertions(+), 16 deletions(-)

diff --git a/crypto/x509/x509_vfy.c b/crypto/x509/x509_vfy.c
index 2f175ca517..bf0c608839 100644
--- a/crypto/x509/x509_vfy.c
+++ b/crypto/x509/x509_vfy.c
@@ -25,6 +25,7 @@
 #include <openssl/objects.h>
 #include <openssl/core_names.h>
 #include "internal/dane.h"
+#include "internal/sslconf.h"
 #include "crypto/x509.h"
 #include "x509_local.h"
 
@@ -3441,14 +3442,31 @@ static int check_sig_level(X509_STORE_CTX *ctx, X509 *cert)
 {
     int secbits = -1;
     int level = ctx->param->auth_level;
+    int nid;
+    OSSL_LIB_CTX *libctx = NULL;
 
     if (level <= 0)
         return 1;
     if (level > NUM_AUTH_LEVELS)
         level = NUM_AUTH_LEVELS;
 
-    if (!X509_get_signature_info(cert, NULL, NULL, &secbits, NULL))
+    if (ctx->libctx)
+        libctx = ctx->libctx;
+    else if (cert->libctx)
+        libctx = cert->libctx;
+    else
+        libctx = OSSL_LIB_CTX_get0_global_default();
+
+    if (!X509_get_signature_info(cert, &nid, NULL, &secbits, NULL))
         return 0;
 
+    if ((nid == NID_sha1 || nid == NID_md5_sha1)
+            && ossl_ctx_legacy_digest_signatures_allowed(libctx, 0)
+            && ctx->param->auth_level < 2)
+        /* When rh-allow-sha1-signatures = yes and security level <= 1,
+         * explicitly allow SHA1 for backwards compatibility. Also allow
+         * MD5-SHA1 because TLS 1.0 is still supported, which uses it. */
+        return 1;
+
     return secbits >= minbits_table[level - 1];
 }
diff --git a/doc/man5/config.pod b/doc/man5/config.pod
index 0c9110d28a..e0516d20b8 100644
--- a/doc/man5/config.pod
+++ b/doc/man5/config.pod
@@ -309,6 +309,13 @@ this option is set to B<no>.  Because TLS 1.1 or lower use MD5-SHA1 as
 pseudorandom function (PRF) to derive key material, disabling
 B<rh-allow-sha1-signatures> requires the use of TLS 1.2 or newer.
 
+Note that enabling B<rh-allow-sha1-signatures> will allow TLS signature
+algorithms that use SHA1 in security level 1, despite the definition of
+security level 1 of 80 bits of security, which SHA1 and MD5-SHA1 do not meet.
+This allows using SHA1 and MD5-SHA1 in TLS in the LEGACY crypto-policy on
+Fedora without requiring to set the security level to 0, which would include
+further insecure algorithms, and thus restores support for TLS 1.0 and 1.1.
+
 =item B<fips_mode> (deprecated)
 
 The value is a boolean that can be B<yes> or B<no>.  If the value is
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index dcd487ec2e..0b50266b69 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -20,6 +20,7 @@
 #include <openssl/bn.h>
 #include <openssl/provider.h>
 #include <openssl/param_build.h>
+#include "crypto/x509.h"
 #include "internal/sslconf.h"
 #include "internal/nelem.h"
 #include "internal/sizes.h"
@@ -1561,19 +1562,28 @@ int tls12_check_peer_sigalg(SSL *s, uint16_t sig, EVP_PKEY *pkey)
         SSLfatal(s, SSL_AD_HANDSHAKE_FAILURE, SSL_R_UNKNOWN_DIGEST);
         return 0;
     }
-    /*
-     * Make sure security callback allows algorithm. For historical
-     * reasons we have to pass the sigalg as a two byte char array.
-     */
-    sigalgstr[0] = (sig >> 8) & 0xff;
-    sigalgstr[1] = sig & 0xff;
-    secbits = sigalg_security_bits(s->ctx, lu);
-    if (secbits == 0 ||
-        !ssl_security(s, SSL_SECOP_SIGALG_CHECK, secbits,
-                      md != NULL ? EVP_MD_get_type(md) : NID_undef,
-                      (void *)sigalgstr)) {
-        SSLfatal(s, SSL_AD_HANDSHAKE_FAILURE, SSL_R_WRONG_SIGNATURE_TYPE);
-        return 0;
+
+    if ((lu->hash == NID_sha1 || lu->hash == NID_md5_sha1)
+            && ossl_ctx_legacy_digest_signatures_allowed(s->ctx->libctx, 0)
+            && SSL_get_security_level(s) < 2) {
+        /* When rh-allow-sha1-signatures = yes and security level <= 1,
+         * explicitly allow SHA1 for backwards compatibility. Also allow
+         * MD5-SHA1 because TLS 1.0 is still supported, which uses it. */
+    } else {
+        /*
+         * Make sure security callback allows algorithm. For historical
+         * reasons we have to pass the sigalg as a two byte char array.
+         */
+        sigalgstr[0] = (sig >> 8) & 0xff;
+        sigalgstr[1] = sig & 0xff;
+        secbits = sigalg_security_bits(s->ctx, lu);
+        if (secbits == 0 ||
+            !ssl_security(s, SSL_SECOP_SIGALG_CHECK, secbits,
+                          md != NULL ? EVP_MD_get_type(md) : NID_undef,
+                          (void *)sigalgstr)) {
+            SSLfatal(s, SSL_AD_HANDSHAKE_FAILURE, SSL_R_WRONG_SIGNATURE_TYPE);
+            return 0;
+        }
     }
     /* Store the sigalg the peer uses */
     s->s3.tmp.peer_sigalg = lu;
@@ -2106,6 +2116,15 @@ static int tls12_sigalg_allowed(const SSL *s, int op, const SIGALG_LOOKUP *lu)
         }
     }
 
+    if ((lu->hash == NID_sha1 || lu->hash == NID_md5_sha1)
+            && ossl_ctx_legacy_digest_signatures_allowed(s->ctx->libctx, 0)
+            && SSL_get_security_level(s) < 2) {
+        /* When rh-allow-sha1-signatures = yes and security level <= 1,
+         * explicitly allow SHA1 for backwards compatibility. Also allow
+         * MD5-SHA1 because TLS 1.0 is still supported, which uses it. */
+        return 1;
+    }
+
     /* Finally see if security callback allows it */
     secbits = sigalg_security_bits(s->ctx, lu);
     sigalgstr[0] = (lu->sigalg >> 8) & 0xff;
@@ -2977,6 +2996,8 @@ static int ssl_security_cert_sig(SSL *s, SSL_CTX *ctx, X509 *x, int op)
 {
     /* Lookup signature algorithm digest */
     int secbits, nid, pknid;
+    OSSL_LIB_CTX *libctx = NULL;
+
     /* Don't check signature if self signed */
     if ((X509_get_extension_flags(x) & EXFLAG_SS) != 0)
         return 1;
@@ -2985,6 +3006,26 @@ static int ssl_security_cert_sig(SSL *s, SSL_CTX *ctx, X509 *x, int op)
     /* If digest NID not defined use signature NID */
     if (nid == NID_undef)
         nid = pknid;
+
+    if (x && x->libctx)
+        libctx = x->libctx;
+    else if (ctx && ctx->libctx)
+        libctx = ctx->libctx;
+    else if (s && s->ctx && s->ctx->libctx)
+        libctx = s->ctx->libctx;
+    else
+        libctx = OSSL_LIB_CTX_get0_global_default();
+
+    if ((nid == NID_sha1 || nid == NID_md5_sha1)
+            && ossl_ctx_legacy_digest_signatures_allowed(libctx, 0)
+            && ((s != NULL && SSL_get_security_level(s) < 2)
+                || (ctx != NULL && SSL_CTX_get_security_level(ctx) < 2)
+            ))
+        /* When rh-allow-sha1-signatures = yes and security level <= 1,
+         * explicitly allow SHA1 for backwards compatibility. Also allow
+         * MD5-SHA1 because TLS 1.0 is still supported, which uses it. */
+        return 1;
+
     if (s)
         return ssl_security(s, op, secbits, nid, x);
     else
diff --git a/test/recipes/25-test_verify.t b/test/recipes/25-test_verify.t
index 700bbd849c..280477bc9d 100644
--- a/test/recipes/25-test_verify.t
+++ b/test/recipes/25-test_verify.t
@@ -387,8 +387,8 @@ ok(verify("ee-pss-sha1-cert", "", ["root-cert"], ["ca-cert"], "-auth_level", "0"
 ok(verify("ee-pss-sha256-cert", "", ["root-cert"], ["ca-cert"], ),
     "CA with PSS signature using SHA256");
 
-ok(!verify("ee-pss-sha1-cert", "", ["root-cert"], ["ca-cert"], "-auth_level", "1"),
-    "Reject PSS signature using SHA1 and auth level 1");
+ok(!verify("ee-pss-sha1-cert", "", ["root-cert"], ["ca-cert"], "-auth_level", "2"),
+    "Reject PSS signature using SHA1 and auth level 2");
 
 ok(verify("ee-pss-sha256-cert", "", ["root-cert"], ["ca-cert"], "-auth_level", "2"),
     "PSS signature using SHA256 and auth level 2");
-- 
2.35.1