1 files changed, 28 insertions, 1 deletions

diff --git a/src/lib/libssl/tls12_record_layer.c b/src/lib/libssl/tls12_record_layer.c
index 04699f9a83..7fa31707d3 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 1.10 2021/01/19 18:34:02 jsing Exp $ */
+/* $OpenBSD: tls12_record_layer.c,v 1.11 2021/01/19 18:51:08 jsing Exp $ */
 /*
  * Copyright (c) 2020 Joel Sing <jsing@openbsd.org>
  *
@@ -168,6 +168,33 @@ tls12_record_layer_alert(struct tls12_record_layer *rl, uint8_t *alert_desc)
         *alert_desc = rl->alert_desc;
 }
 
+int
+tls12_record_layer_write_overhead(struct tls12_record_layer *rl,
+    size_t *overhead)
+{
+        size_t block_size, eiv_len, mac_len;
+
+        *overhead = 0;
+
+        if (rl->write->aead_ctx != NULL) {
+                *overhead = rl->write->aead_ctx->tag_len;
+        } else if (rl->write->cipher_ctx != NULL) {
+                eiv_len = 0;
+                if (rl->version != TLS1_VERSION) {
+                        if (!tls12_record_protection_eiv_len(rl->write, &eiv_len))
+                                return 0;
+                }
+                if (!tls12_record_protection_block_size(rl->write, &block_size))
+                        return 0;
+                if (!tls12_record_protection_mac_len(rl->write, &mac_len))
+                        return 0;
+
+                *overhead = eiv_len + block_size + mac_len;
+        }
+
+        return 1;
+}
+
 void
 tls12_record_layer_set_version(struct tls12_record_layer *rl, uint16_t version)
 {