Hi,
When X11 connection is forwarded using ssh, the ssh client typically connects
to the local X server using unix socket (often it is the only option because X
servers no longer listens on TCP by default). X clients connected remotely
over ssh then seem like if they are local to the X server. Because of that it
will attempt to use extensions that are meant for local clients only (SHM,
DRI*, etc). In most cases the client or server can detect failure and fallback
to a method that works remotely, but this does not always work:
https://bugzilla.opensuse.org/show_bug.cgi?id=1022727
(comments 24-26)
The ideal solution would be if ssh marked the connection as remote.
X protocol supports that since 2011:
https://cgit.freedesktop.org/xorg/xserver/commit/?
id=e2c7d70e5ddb8b17676a13ceebfbb87d14d63243
SSH only needs to change the first byte sent from X client to server to mark
it as remote. SSH already modifies the whole first message (replaces
authorization data), so changing the first byte is easy addition.
I have attached patch that implements it. Please check it and consider adding
it or something similar to openssh.
Best regards,
Michal Srb
>From 0ab799d99113fd20e918fb2bc740614ce8388dcb Mon Sep 17 00:00:00 2001
From: Michal Srb <msrb@xxxxxxxx>
Date: Mon, 21 Aug 2017 15:49:38 +0200
Subject: [PATCH] Mark x11 connection as remote.
If we are channeling x11 connection, modify the byte order field to let
X server know that the connection is remote.
---
channels.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/channels.c b/channels.c
index 028d5db2..2a09f91a 100644
--- a/channels.c
+++ b/channels.c
@@ -931,10 +931,12 @@ x11_open_helper(Buffer *b)
/* Parse the lengths of variable-length fields. */
ucp = buffer_ptr(b);
- if (ucp[0] == 0x42) { /* Byte order MSB first. */
+ if (ucp[0] == 0x42 || ucp[0] == 0x52) { /* Byte order MSB first. */
+ ucp[0] = 0x52; /* MSB first + remote connection flag */
proto_len = 256 * ucp[6] + ucp[7];
data_len = 256 * ucp[8] + ucp[9];
- } else if (ucp[0] == 0x6c) { /* Byte order LSB first. */
+ } else if (ucp[0] == 0x6c || ucp[0] == 0x72) { /* Byte order LSB first. */
+ ucp[0] = 0x72; /* LSB first + remote connection flag */
proto_len = ucp[6] + 256 * ucp[7];
data_len = ucp[8] + 256 * ucp[9];
} else {
--
2.12.3
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