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[Qemu-devel] [PULL 13/18] chardev: disallow TLS/telnet/websocket with tc

From: Marc-André Lureau
Subject: [Qemu-devel] [PULL 13/18] chardev: disallow TLS/telnet/websocket with tcp_chr_wait_connected
Date: Thu, 7 Feb 2019 17:06:12 +0100

From: Daniel P. Berrangé <address@hidden>

In the previous commit

    commit 1dc8a6695c731abb7461c637b2512c3670d82be4
    Author: Marc-André Lureau <address@hidden>
    Date:   Tue Aug 16 12:33:32 2016 +0400

      char: fix waiting for TLS and telnet connection

the tcp_chr_wait_connected() method was changed to check for a non-NULL
's->ioc' as a sign that there is already a connection present, as
opposed to checking the "connected" flag to supposedly fix handling of
TLS/telnet connections.

The original code would repeatedly call tcp_chr_wait_connected creating
many connections as 'connected' would never become true. The changed
code would still repeatedly call tcp_chr_wait_connected busy waiting
because s->ioc is set but the chardev will never see CHR_EVENT_OPENED.
IOW, the code is still broken with TLS/telnet, but in a different way.

Checking for a non-NULL 's->ioc' does not mean that a CHR_EVENT_OPENED
will be ready for a TLS/telnet connection. These protocols (and the
websocket protocol) all require the main loop to be running in order
to complete the protocol handshake before emitting CHR_EVENT_OPENED.
The tcp_chr_wait_connected() method is only used during early startup
before a main loop is running, so TLS/telnet/websock connections can
never complete initialization.

Making this work would require changing tcp_chr_wait_connected to run
a main loop. This is quite complex since we must not allow GSource's
that other parts of QEMU have registered to run yet. The current callers
of tcp_chr_wait_connected do not require use of the TLS/telnet/websocket
protocols, so the simplest option is to just forbid this combination
completely for now.

Reviewed-by: Marc-André Lureau <address@hidden>
Signed-off-by: Daniel P. Berrangé <address@hidden>
Message-Id: <address@hidden>
 chardev/char-socket.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index 7db20ff0a0..86c1f502d6 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -951,8 +951,20 @@ static void tcp_chr_accept_server_sync(Chardev *chr)
 static int tcp_chr_wait_connected(Chardev *chr, Error **errp)
     SocketChardev *s = SOCKET_CHARDEV(chr);
-    /* It can't wait on s->connected, since it is set asynchronously
-     * in TLS and telnet cases, only wait for an accepted socket */
+    const char *opts[] = { "telnet", "tn3270", "websock", "tls-creds" };
+    bool optset[] = { s->is_telnet, s->is_tn3270, s->is_websock, s->tls_creds 
+    size_t i;
+    for (i = 0; i < G_N_ELEMENTS(opts); i++) {
+        if (optset[i]) {
+            error_setg(errp,
+                       "'%s' option is incompatible with waiting for "
+                       "connection completion", opts[i]);
+            return -1;
+        }
+    }
     while (!s->ioc) {
         if (s->is_listen) {

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