1 files changed, 42 insertions, 5 deletions

diff --git a/src/lib/libssl/tls12_record_layer.c b/src/lib/libssl/tls12_record_layer.c
index ba3c3dfb2b..6cf8b31c63 100644
--- a/src/lib/libssl/tls12_record_layer.c
+++ b/src/lib/libssl/tls12_record_layer.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls12_record_layer.c,v 1.24 2021/03/21 19:08:22 tb Exp $ */
+/* $OpenBSD: tls12_record_layer.c,v 1.25 2021/03/29 16:19:15 jsing Exp $ */
 /*
  * Copyright (c) 2020 Joel Sing <jsing@openbsd.org>
  *
@@ -22,9 +22,11 @@
 
 #include "ssl_locl.h"
 
+#define TLS12_RECORD_SEQ_NUM_LEN 8
+
 struct tls12_record_protection {
         uint16_t epoch;
-        uint8_t seq_num[SSL3_SEQUENCE_SIZE];
+        uint8_t seq_num[TLS12_RECORD_SEQ_NUM_LEN];
 
         SSL_AEAD_CTX *aead_ctx;
 
@@ -342,6 +344,38 @@ tls12_record_layer_reflect_seq_num(struct tls12_record_layer *rl)
             sizeof(rl->write->seq_num));
 }
 
+static const uint8_t tls12_max_seq_num[TLS12_RECORD_SEQ_NUM_LEN] = {
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+};
+
+int
+tls12_record_layer_inc_seq_num(struct tls12_record_layer *rl, uint8_t *seq_num)
+{
+        CBS max_seq_num;
+        int i;
+
+        /*
+         * RFC 5246 section 6.1 and RFC 6347 section 4.1 - both TLS and DTLS
+         * sequence numbers must not wrap. Note that for DTLS the first two
+         * bytes are used as an "epoch" and not part of the sequence number.
+         */
+        CBS_init(&max_seq_num, seq_num, TLS12_RECORD_SEQ_NUM_LEN);
+        if (rl->dtls) {
+                if (!CBS_skip(&max_seq_num, 2))
+                        return 0;
+        }
+        if (CBS_mem_equal(&max_seq_num, tls12_max_seq_num,
+            CBS_len(&max_seq_num)))
+                return 0;
+
+        for (i = TLS12_RECORD_SEQ_NUM_LEN - 1; i >= 0; i--) {
+                if (++seq_num[i] != 0)
+                        break;
+        }
+
+        return 1;
+}
+
 static int
 tls12_record_layer_set_mac_key(struct tls12_record_protection *rp,
     const uint8_t *mac_key, size_t mac_key_len)
@@ -1074,8 +1108,10 @@ tls12_record_layer_open_record(struct tls12_record_layer *rl, uint8_t *buf,
                         return 0;
         }
 
-        if (!rl->dtls)
-                tls1_record_sequence_increment(rl->read->seq_num);
+        if (!rl->dtls) {
+                if (!tls12_record_layer_inc_seq_num(rl, rl->read->seq_num))
+                        return 0;
+        }
 
         return 1;
 }
@@ -1274,7 +1310,8 @@ tls12_record_layer_seal_record(struct tls12_record_layer *rl,
         if (!CBB_flush(cbb))
                 goto err;
 
-        tls1_record_sequence_increment(rl->write->seq_num);
+        if (!tls12_record_layer_inc_seq_num(rl, rl->write->seq_num))
+                goto err;
 
         ret = 1;