TLS: Fail without exception when decrypting truncated records

On truncated TLS records, just fail when attempting to decrypt or
calculate the handshake hash instead of raising an BoundsError.
The appropriate exception will be raised later when fields are
actually added to the tree.

This only makes a difference on the first pass, especially with
unencrypted initial handshake messages, as we don't try to decrypt
or calculate the hash on the second pass.

Fix #18896

1 files changed, 7 insertions, 2 deletions

diff --git a/epan/dissectors/packet-tls.c b/epan/dissectors/packet-tls.c
index cd2677dede..c2b630c0c7 100644
--- a/epan/dissectors/packet-tls.c
+++ b/epan/dissectors/packet-tls.c
@@ -1166,7 +1166,7 @@ decrypt_ssl3_record(tvbuff_t *tvb, packet_info *pinfo, guint32 offset, SslDecryp
     gboolean    success;
     gint        direction;
     StringInfo *data_for_iv;
-    gint        data_for_iv_len;
+    gint        data_for_iv_len, data_for_iv_offset;
     SslDecoder *decoder;
 
     /* if we can decrypt and decryption was a success
@@ -1188,7 +1188,12 @@ decrypt_ssl3_record(tvbuff_t *tvb, packet_info *pinfo, guint32 offset, SslDecryp
     /* save data to update IV if decoder is available or updated later */
     data_for_iv = (direction != 0) ? &ssl->server_data_for_iv : &ssl->client_data_for_iv;
     data_for_iv_len = (record_length < 24) ? record_length : 24;
-    ssl_data_set(data_for_iv, (const guchar*)tvb_get_ptr(tvb, offset + record_length - data_for_iv_len, data_for_iv_len), data_for_iv_len);
+    data_for_iv_offset = offset + record_length - data_for_iv_len;
+    if (!tvb_bytes_exist(tvb, data_for_iv_offset, data_for_iv_len)) {
+        ssl_debug_printf("decrypt_ssl3_record: record truncated\n");
+        return FALSE;
+    }
+    ssl_data_set(data_for_iv, (const guchar*)tvb_get_ptr(tvb, data_for_iv_offset, data_for_iv_len), data_for_iv_len);
 
     if (!decoder) {
         ssl_debug_printf("decrypt_ssl3_record: no decoder available\n");