Ensure RSA PSS correctly returns the right default digest

A default digest of SHA256 was being returned for RSA PSS even if the
PSS parameters indicated a different digest must be used. We change this
so that the correct default digest is returned and additionally mark this
as mandatory for PSS.

This bug had an impact on sig alg selection in libssl. Due to this issue
an incorrect sig alg might be selected in the event that a server is
configured with an RSA-PSS cert with parameter restrictions.

Fixes #9545

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9553)

diff --git a/crypto/rsa/rsa_ameth.c b/crypto/rsa/rsa_ameth.c
index 82d1d56d0a19e0eeec9e76c401a4a8bc29bc4a73..bf56039b468d4dcfd05c282cefc00b9c5e9581c6 100644 (file)
--- a/crypto/rsa/rsa_ameth.c
+++ b/crypto/rsa/rsa_ameth.c
@@ -458,6 +458,9 @@ static int rsa_sig_print(BIO *bp, const X509_ALGOR *sigalg,
 static int rsa_pkey_ctrl(EVP_PKEY *pkey, int op, long arg1, void *arg2)
 {
     X509_ALGOR *alg = NULL;
+    const EVP_MD *md;
+    const EVP_MD *mgf1md;
+    int min_saltlen;
 
     switch (op) {
 
@@ -497,6 +500,16 @@ static int rsa_pkey_ctrl(EVP_PKEY *pkey, int op, long arg1, void *arg2)
 #endif
 
     case ASN1_PKEY_CTRL_DEFAULT_MD_NID:
+        if (pkey->pkey.rsa->pss != NULL) {
+            if (!rsa_pss_get_param(pkey->pkey.rsa->pss, &md, &mgf1md,
+                                   &min_saltlen)) {
+                RSAerr(0, ERR_R_INTERNAL_ERROR);
+                return 0;
+            }
+            *(int *)arg2 = EVP_MD_type(md);
+            /* Return of 2 indicates this MD is mandatory */
+            return 2;
+        }
         *(int *)arg2 = NID_sha256;
         return 1;