Ensure that we write out alerts correctly after early_data

If we sent early_data and then received back an HRR, the enc_write_ctx
was stale resulting in errors if an alert needed to be sent.

Thanks to Quarkslab for reporting this.

In any case it makes little sense to encrypt alerts using the
client_early_traffic_secret, so we add special handling for alerts sent
after early_data. All such alerts are sent in plaintext.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6887)

ssl/record/rec_layer_s3.c

@@ -829,7 +829,10 @@ int do_ssl3_write(SSL *s, int type, const unsigned char *buf,
          * In TLSv1.3, once encrypting, we always use application data for the
          * record type
          */
-        if (SSL_TREAT_AS_TLS13(s) && s->enc_write_ctx != NULL)
+        if (SSL_TREAT_AS_TLS13(s)
+                && s->enc_write_ctx != NULL
+                && (s->statem.enc_write_state != ENC_WRITE_STATE_WRITE_PLAIN_ALERTS
+                    || type != SSL3_RT_ALERT))
             rectype = SSL3_RT_APPLICATION_DATA;
         else
             rectype = type;
@@ -892,7 +895,10 @@ int do_ssl3_write(SSL *s, int type, const unsigned char *buf,
             SSL3_RECORD_reset_input(&wr[j]);
         }
 
-        if (SSL_TREAT_AS_TLS13(s) && s->enc_write_ctx != NULL) {
+        if (SSL_TREAT_AS_TLS13(s)
+                && s->enc_write_ctx != NULL
+                && (s->statem.enc_write_state != ENC_WRITE_STATE_WRITE_PLAIN_ALERTS
+                    || type != SSL3_RT_ALERT)) {
             size_t rlen, max_send_fragment;
 
             if (!WPACKET_put_bytes_u8(thispkt, type)) {
@@ -981,8 +987,7 @@ int do_ssl3_write(SSL *s, int type, const unsigned char *buf,
         SSL3_RECORD_set_length(thiswr, len);
     }
 
-    if (s->early_data_state == SSL_EARLY_DATA_WRITING
-            || s->early_data_state == SSL_EARLY_DATA_WRITE_RETRY) {
+    if (s->statem.enc_write_state == ENC_WRITE_STATE_WRITE_PLAIN_ALERTS) {
         /*
          * We haven't actually negotiated the version yet, but we're trying to
          * send early data - so we need to use the tls13enc function.

ssl/record/ssl3_record_tls13.c

@@ -52,7 +52,10 @@ int tls13_enc(SSL *s, SSL3_RECORD *recs, size_t n_recs, int sending)
         seq = RECORD_LAYER_get_read_sequence(&s->rlayer);
     }
 
-    if (ctx == NULL) {
+    if (ctx == NULL
+            || (rec->type == SSL3_RT_ALERT
+                && s->statem.enc_write_state
+                   == ENC_WRITE_STATE_WRITE_PLAIN_ALERTS)) {
         memmove(rec->data, rec->input, rec->length);
         rec->input = rec->data;
         return 1;

ssl/s3_enc.c

@@ -155,7 +155,7 @@ int ssl3_change_cipher_state(SSL *s, int which)
         RECORD_LAYER_reset_read_sequence(&s->rlayer);
         mac_secret = &(s->s3->read_mac_secret[0]);
     } else {
-        s->statem.invalid_enc_write_ctx = 1;
+        s->statem.enc_write_state = ENC_WRITE_STATE_INVALID;
         if (s->enc_write_ctx != NULL) {
             reuse_dd = 1;
         } else if ((s->enc_write_ctx = EVP_CIPHER_CTX_new()) == NULL) {
@@ -238,7 +238,7 @@ int ssl3_change_cipher_state(SSL *s, int which)
         goto err;
     }
 
-    s->statem.invalid_enc_write_ctx = 0;
+    s->statem.enc_write_state = ENC_WRITE_STATE_VALID;
     OPENSSL_cleanse(exp_key, sizeof(exp_key));
     OPENSSL_cleanse(exp_iv, sizeof(exp_iv));
     return 1;

ssl/statem/statem.c

@@ -123,7 +123,8 @@ void ossl_statem_fatal(SSL *s, int al, int func, int reason, const char *file,
     s->statem.in_init = 1;
     s->statem.state = MSG_FLOW_ERROR;
     ERR_put_error(ERR_LIB_SSL, func, reason, file, line);
-    if (al != SSL_AD_NO_ALERT && !s->statem.invalid_enc_write_ctx)
+    if (al != SSL_AD_NO_ALERT
+            && s->statem.enc_write_state != ENC_WRITE_STATE_INVALID)
         ssl3_send_alert(s, SSL3_AL_FATAL, al);
 }
 

ssl/statem/statem.h

@@ -71,6 +71,15 @@ typedef enum {
     WRITE_STATE_POST_WORK
 } WRITE_STATE;
 
+typedef enum {
+    /* The enc_write_ctx can be used normally */
+    ENC_WRITE_STATE_VALID,
+    /* The enc_write_ctx cannot be used */
+    ENC_WRITE_STATE_INVALID,
+    /* Write alerts in plaintext, but otherwise use the enc_write_ctx */
+    ENC_WRITE_STATE_WRITE_PLAIN_ALERTS
+} ENC_WRITE_STATES;
+
 /*****************************************************************************
  *                                                                           *
  * This structure should be considered "opaque" to anything outside of the   *
@@ -100,7 +109,7 @@ struct ossl_statem_st {
     /* Should we skip the CertificateVerify message? */
     unsigned int no_cert_verify;
     int use_timer;
-    int invalid_enc_write_ctx;
+    ENC_WRITE_STATES enc_write_state;
 };
 typedef struct ossl_statem_st OSSL_STATEM;
 

ssl/t1_enc.c

@@ -154,7 +154,7 @@ int tls1_change_cipher_state(SSL *s, int which)
         mac_secret = &(s->s3->read_mac_secret[0]);
         mac_secret_size = &(s->s3->read_mac_secret_size);
     } else {
-        s->statem.invalid_enc_write_ctx = 1;
+        s->statem.enc_write_state = ENC_WRITE_STATE_INVALID;
         if (s->ext.use_etm)
             s->s3->flags |= TLS1_FLAGS_ENCRYPT_THEN_MAC_WRITE;
         else
@@ -316,7 +316,7 @@ int tls1_change_cipher_state(SSL *s, int which)
                  ERR_R_INTERNAL_ERROR);
         goto err;
     }
-    s->statem.invalid_enc_write_ctx = 0;
+    s->statem.enc_write_state = ENC_WRITE_STATE_VALID;
 
 #ifdef SSL_DEBUG
     printf("which = %04X\nkey=", which);

ssl/tls13_enc.c

@@ -425,7 +425,7 @@ int tls13_change_cipher_state(SSL *s, int which)
 
         RECORD_LAYER_reset_read_sequence(&s->rlayer);
     } else {
-        s->statem.invalid_enc_write_ctx = 1;
+        s->statem.enc_write_state = ENC_WRITE_STATE_INVALID;
         if (s->enc_write_ctx != NULL) {
             EVP_CIPHER_CTX_reset(s->enc_write_ctx);
         } else {
@@ -648,7 +648,10 @@ int tls13_change_cipher_state(SSL *s, int which)
         goto err;
     }
 
-    s->statem.invalid_enc_write_ctx = 0;
+    if (!s->server && label == client_early_traffic)
+        s->statem.enc_write_state = ENC_WRITE_STATE_WRITE_PLAIN_ALERTS;
+    else
+        s->statem.enc_write_state = ENC_WRITE_STATE_VALID;
     ret = 1;
  err:
     OPENSSL_cleanse(secret, sizeof(secret));
@@ -671,7 +674,7 @@ int tls13_update_key(SSL *s, int sending)
         insecret = s->client_app_traffic_secret;
 
     if (sending) {
-        s->statem.invalid_enc_write_ctx = 1;
+        s->statem.enc_write_state = ENC_WRITE_STATE_INVALID;
         iv = s->write_iv;
         ciph_ctx = s->enc_write_ctx;
         RECORD_LAYER_reset_write_sequence(&s->rlayer);
@@ -692,7 +695,7 @@ int tls13_update_key(SSL *s, int sending)
 
     memcpy(insecret, secret, hashlen);
 
-    s->statem.invalid_enc_write_ctx = 0;
+    s->statem.enc_write_state = ENC_WRITE_STATE_VALID;
     ret = 1;
  err:
     OPENSSL_cleanse(secret, sizeof(secret));