From 24f4f8fffa984d32e2f41d2af90743c6a8a3841d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Helleu?= <flashcode@flashtux.org>
Date: Tue, 7 Sep 2021 19:05:06 +0200
Subject: [PATCH] relay: fix crash when decoding a malformed websocket frame
 (CVE-2021-40516)

---
 ChangeLog.adoc                      |  7 +++++++
 src/plugins/relay/relay-websocket.c | 16 +++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/ChangeLog.adoc b/ChangeLog.adoc
index f99e5eaee..aafeab075 100644
--- a/ChangeLog.adoc
+++ b/ChangeLog.adoc
@@ -15,6 +15,13 @@ https://weechat.org/files/releasenotes/ReleaseNotes-devel.html[release notes]
 (file _ReleaseNotes.adoc_ in sources).
 
 
+[[v2.3.1]]
+== Version 2.3.1 (under dev)
+
+Bug fixes::
+
+  * relay: fix crash when decoding a malformed websocket frame (CVE-2021-40516)
+
 [[v2.3]]
 == Version 2.3 (2018-10-21)
 
diff --git a/src/plugins/relay/relay-websocket.c b/src/plugins/relay/relay-websocket.c
index bbac751dc..7cbe60826 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++)
         {
@@ -323,6 +324,11 @@ 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];