From 535aaf2325356d517acb761cf81e7bd33ed6dbc4 Mon Sep 17 00:00:00 2001
From: Juliusz Sosinowicz <juliusz@wolfssl.com>
Date: Wed, 15 Apr 2026 14:43:26 +0200
Subject: [PATCH] tls: fix TLSX_TCA_GetSize word16 overflow (F-2131)

Mirror the TLSX_SNI_GetSize pattern: accumulate into a word32 and
return 0 when the aggregate size exceeds WOLFSSL_MAX_16BIT so large
idSz values or many TCA entries no longer silently wrap to a small
value that undersizes the TLSX_TCA_Write output buffer.
---
 src/tls.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/tls.c b/src/tls.c
index dde6a335a9..e94634f149 100644
--- a/src/tls.c
+++ b/src/tls.c
@@ -2961,7 +2961,7 @@ static void TLSX_TCA_FreeAll(TCA* list, void* heap)
 static word16 TLSX_TCA_GetSize(TCA* list)
 {
     TCA* tca;
-    word16 length = OPAQUE16_LEN; /* list length */
+    word32 length = OPAQUE16_LEN; /* list length */
 
     while ((tca = list)) {
         list = tca->next;
@@ -2979,9 +2979,13 @@ static word16 TLSX_TCA_GetSize(TCA* list)
                 length += OPAQUE16_LEN + tca->idSz;
                 break;
         }
+
+        if (length > WOLFSSL_MAX_16BIT) {
+            return 0;
+        }
     }
 
-    return length;
+    return (word16)length;
 }
 
 /** Writes the TCA objects of a list in a buffer. */
@@ -14941,8 +14945,15 @@ static int TLSX_GetSize(TLSX* list, byte* semaphore, byte msgType,
 
             case TLSX_TRUSTED_CA_KEYS:
                 /* TCA only sends the list on the request. */
-                if (isRequest)
-                    length += TCA_GET_SIZE((TCA*)extension->data);
+                if (isRequest) {
+                    word16 tcaSz = TCA_GET_SIZE((TCA*)extension->data);
+                    /* 0 on non-empty list means 16-bit overflow. */
+                    if (tcaSz == 0 && extension->data != NULL) {
+                        ret = LENGTH_ERROR;
+                        break;
+                    }
+                    length += tcaSz;
+                }
                 break;
 
             case TLSX_MAX_FRAGMENT_LENGTH: