From 620c97b671a9c7bc31ca36a24b2242aa1aa80022 Mon Sep 17 00:00:00 2001
From: Kurt Roeckx <kurt@roeckx.be>
Date: Sun, 9 Feb 2020 19:28:15 +0100
Subject: Check that ed25519 and ed448 are allowed by the security level

Signature algorithms not using an MD weren't checked that they're
allowed by the security level.

Reviewed-by: Matt Caswell <matt@openssl.org>
GH: #10785
---
 ssl/t1_lib.c | 59 +++++++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 41 insertions(+), 18 deletions(-)

(limited to 'ssl')

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 103a8f18bb..aedb521015 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -1075,6 +1075,31 @@ int tls_check_sigalg_curve(const SSL *s, int curve)
 }
 #endif
 
+/*
+ * Return the number of security bits for the signature algorithm, or 0 on
+ * error.
+ */
+static int sigalg_security_bits(SSL_CTX *ctx, const SIGALG_LOOKUP *lu)
+{
+    const EVP_MD *md = NULL;
+    int secbits = 0;
+
+    if (!tls1_lookup_md(ctx, lu, &md))
+        return 0;
+    if (md != NULL)
+    {
+        /* Security bits: half digest bits */
+        secbits = EVP_MD_size(md) * 4;
+    } else {
+        /* Values from https://tools.ietf.org/html/rfc8032#section-8.5 */
+        if (lu->sigalg == TLSEXT_SIGALG_ed25519)
+            secbits = 128;
+        else if (lu->sigalg == TLSEXT_SIGALG_ed448)
+            secbits = 224;
+    }
+    return secbits;
+}
+
 /*
  * Check signature algorithm is consistent with sent supported signature
  * algorithms and if so set relevant digest and signature scheme in
@@ -1088,6 +1113,7 @@ int tls12_check_peer_sigalg(SSL *s, uint16_t sig, EVP_PKEY *pkey)
     size_t sent_sigslen, i, cidx;
     int pkeyid = EVP_PKEY_id(pkey);
     const SIGALG_LOOKUP *lu;
+    int secbits = 0;
 
     /* Should never happen */
     if (pkeyid == -1)
@@ -1189,20 +1215,20 @@ int tls12_check_peer_sigalg(SSL *s, uint16_t sig, EVP_PKEY *pkey)
                  SSL_R_UNKNOWN_DIGEST);
         return 0;
     }
-    if (md != NULL) {
-        /*
-         * 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;
-        if (!ssl_security(s, SSL_SECOP_SIGALG_CHECK,
-                    EVP_MD_size(md) * 4, EVP_MD_type(md),
-                    (void *)sigalgstr)) {
-            SSLfatal(s, SSL_AD_HANDSHAKE_FAILURE, SSL_F_TLS12_CHECK_PEER_SIGALG,
-                     SSL_R_WRONG_SIGNATURE_TYPE);
-            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_type(md) : NID_undef,
+                      (void *)sigalgstr)) {
+        SSLfatal(s, SSL_AD_HANDSHAKE_FAILURE, SSL_F_TLS12_CHECK_PEER_SIGALG,
+                 SSL_R_WRONG_SIGNATURE_TYPE);
+        return 0;
     }
     /* Store the sigalg the peer uses */
     s->s3.tmp.peer_sigalg = lu;
@@ -1726,11 +1752,8 @@ static int tls12_sigalg_allowed(const SSL *s, int op, const SIGALG_LOOKUP *lu)
         }
     }
 
-    if (lu->hash == NID_undef)
-        return 1;
-    /* Security bits: half digest bits */
-    secbits = EVP_MD_size(ssl_md(s->ctx, lu->hash_idx)) * 4;
     /* Finally see if security callback allows it */
+    secbits = sigalg_security_bits(s->ctx, lu);
     sigalgstr[0] = (lu->sigalg >> 8) & 0xff;
     sigalgstr[1] = lu->sigalg & 0xff;
     return ssl_security(s, op, secbits, lu->hash, (void *)sigalgstr);
-- 
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