smime/pkcs7: disable the Bleichenbacher workaround

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #13817)

crypto/pkcs7/pk7_doit.c

@@ -163,6 +163,13 @@ static int pkcs7_decrypt_rinfo(unsigned char **pek, int *peklen,
     if (EVP_PKEY_decrypt_init(pctx) <= 0)
         goto err;
 
+    if (EVP_PKEY_is_a(pkey, "RSA"))
+        /* upper layer pkcs7 code incorrectly assumes that a successful RSA
+         * decryption means that the key matches ciphertext (which never
+         * was the case, implicit rejection or not), so to make it work
+         * disable implicit rejection for RSA keys */
+        EVP_PKEY_CTX_ctrl_str(pctx, "rsa_pkcs1_implicit_rejection", "0");
+
     if (EVP_PKEY_decrypt(pctx, NULL, &eklen,
                          ri->enc_key->data, ri->enc_key->length) <= 0)
         goto err;