From badb16c481cf592a1761ad20dd0a84614d2bbd5b Mon Sep 17 00:00:00 2001
From: David Rheinsberg <david.rheinsberg@gmail.com>
Date: Thu, 14 Mar 2019 13:33:28 +0100
Subject: [PATCH] sd-bus: fix SASL reply to empty AUTH

The correct way to reply to "AUTH <protocol>" without any payload is to
send "DATA" rather than "OK". The "DATA" reply triggers the client to
respond with the requested payload.

In fact, adding the data as hex-encoded argument like
"AUTH <protocol> <hex-data>" is an optimization that skips the "DATA"
roundtrip. The standard way to perform an authentication is to send the
"DATA" line.

This commit fixes sd-bus to properly send the "DATA" line. Surprisingly
no existing implementation depends on this, as they all pass the data
directly as argument to "AUTH". This will not work if we want to pass
an empty argument, though.

Signed-off-by: David Rheinsberg <david.rheinsberg@gmail.com>
(cherry picked from commit 2010873b4b49b223e0cc07d28205b09c693ef005)

Related: #1838081
---
 src/libsystemd/sd-bus/bus-socket.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/libsystemd/sd-bus/bus-socket.c b/src/libsystemd/sd-bus/bus-socket.c
index 1c8b331b48..e505d43c6b 100644
--- a/src/libsystemd/sd-bus/bus-socket.c
+++ b/src/libsystemd/sd-bus/bus-socket.c
@@ -399,7 +399,10 @@ static int bus_socket_auth_verify_server(sd_bus *b) {
                                 r = bus_socket_auth_write(b, "REJECTED\r\n");
                         else {
                                 b->auth = BUS_AUTH_ANONYMOUS;
-                                r = bus_socket_auth_write_ok(b);
+                                if (l <= strlen("AUTH ANONYMOUS"))
+                                        r = bus_socket_auth_write(b, "DATA\r\n");
+                                else
+                                        r = bus_socket_auth_write_ok(b);
                         }
 
                 } else if (line_begins(line, l, "AUTH EXTERNAL")) {
@@ -413,7 +416,10 @@ static int bus_socket_auth_verify_server(sd_bus *b) {
                                 r = bus_socket_auth_write(b, "REJECTED\r\n");
                         else {
                                 b->auth = BUS_AUTH_EXTERNAL;
-                                r = bus_socket_auth_write_ok(b);
+                                if (l <= strlen("AUTH EXTERNAL"))
+                                        r = bus_socket_auth_write(b, "DATA\r\n");
+                                else
+                                        r = bus_socket_auth_write_ok(b);
                         }
 
                 } else if (line_begins(line, l, "AUTH"))