From 97bdd51112ad290647c208c13c4916a1630caa0f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Helleu?= <flashcode@flashtux.org>
Date: Sat, 4 Sep 2021 15:55:37 +0200
Subject: [PATCH] relay: fix crash when decoding a malformed websocket frame

---
 ChangeLog.adoc                      |  1 +
 src/plugins/relay/relay-websocket.c | 16 +++++++++++-----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/ChangeLog.adoc b/ChangeLog.adoc
index 2165b202d..9339d1b28 100644
--- a/ChangeLog.adoc
+++ b/ChangeLog.adoc
@@ -50,6 +50,7 @@ Bug fixes::
   * irc: remove unneeded message about Diffie-Hellman shared secret exchange during SSL connection to server (issue #857)
   * irc: escape/unescape IRC message tags values (issue #1654)
   * irc: set notify level to "private" for received WALLOPS
+  * relay: fix crash when decoding a malformed websocket frame
   * script: fix move of installed script on another filesystem (issue #1667)
 
 Documentation::
diff --git a/src/plugins/relay/relay-websocket.c b/src/plugins/relay/relay-websocket.c
index c5a7df324..7cbbaa308 100644
--- a/src/plugins/relay/relay-websocket.c
+++ b/src/plugins/relay/relay-websocket.c
@@ -278,7 +278,7 @@ relay_websocket_decode_frame (const unsigned char *buffer,
     index_buffer = 0;
 
     /* loop to decode all frames in message */
-    while (index_buffer + 2 <= buffer_length)
+    while (index_buffer + 1 < buffer_length)
     {
         opcode = buffer[index_buffer] & 15;
 
@@ -293,10 +293,12 @@ relay_websocket_decode_frame (const unsigned char *buffer,
         length_frame_size = 1;
         length_frame = buffer[index_buffer + 1] & 127;
         index_buffer += 2;
+        if (index_buffer >= buffer_length)
+            return 0;
         if ((length_frame == 126) || (length_frame == 127))
         {
             length_frame_size = (length_frame == 126) ? 2 : 8;
-            if (buffer_length < 1 + length_frame_size)
+            if (index_buffer + length_frame_size > buffer_length)
                 return 0;
             length_frame = 0;
             for (i = 0; i < length_frame_size; i++)
@@ -306,10 +308,9 @@ relay_websocket_decode_frame (const unsigned char *buffer,
             index_buffer += length_frame_size;
         }
 
-        if (buffer_length < 1 + length_frame_size + 4 + length_frame)
-            return 0;
-
         /* read masks (4 bytes) */
+        if (index_buffer + 4 > buffer_length)
+            return 0;
         int masks[4];
         for (i = 0; i < 4; i++)
         {
@@ -333,6 +334,11 @@ relay_websocket_decode_frame (const unsigned char *buffer,
         *decoded_length += 1;
 
         /* decode data using masks */
+        if ((length_frame > buffer_length)
+            || (index_buffer + length_frame > buffer_length))
+        {
+            return 0;
+        }
         for (i = 0; i < length_frame; i++)
         {
             decoded[*decoded_length + i] = (int)((unsigned char)buffer[index_buffer + i]) ^ masks[i % 4];