From 4573166e9384f4ffe17a87f7b41aacc4cfe8bad0 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 13 Feb 2019 16:51:22 +0100
Subject: [PATCH] sd-bus: if we receive an invalid dbus message, ignore and
 proceeed

dbus-daemon might have a slightly different idea of what a valid msg is
than us (for example regarding valid msg and field sizes). Let's hence
try to proceed if we can and thus drop messages rather than fail the
connection if we fail to validate a message.

Hopefully the differences in what is considered valid are not visible
for real-life usecases, but are specific to exploit attempts only.

(cherry-picked from commit 6d586a13717ae057aa1b4127400c3de61cd5b9e7)

Related: #1678641
---
 src/libsystemd/sd-bus/bus-socket.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/libsystemd/sd-bus/bus-socket.c b/src/libsystemd/sd-bus/bus-socket.c
index a5513d1ab..17cfa8e1f 100644
--- a/src/libsystemd/sd-bus/bus-socket.c
+++ b/src/libsystemd/sd-bus/bus-socket.c
@@ -1078,7 +1078,7 @@ static int bus_socket_read_message_need(sd_bus *bus, size_t *need) {
 }
 
 static int bus_socket_make_message(sd_bus *bus, size_t size) {
-        sd_bus_message *t;
+        sd_bus_message *t = NULL;
         void *b;
         int r;
 
@@ -1103,7 +1103,9 @@ static int bus_socket_make_message(sd_bus *bus, size_t size) {
                                     bus->fds, bus->n_fds,
                                     NULL,
                                     &t);
-        if (r < 0) {
+        if (r == -EBADMSG)
+                log_debug_errno(r, "Received invalid message from connection %s, dropping.", strna(bus->description));
+        else if (r < 0) {
                 free(b);
                 return r;
         }
@@ -1114,7 +1116,8 @@ static int bus_socket_make_message(sd_bus *bus, size_t size) {
         bus->fds = NULL;
         bus->n_fds = 0;
 
-        bus->rqueue[bus->rqueue_size++] = t;
+        if (t)
+                bus->rqueue[bus->rqueue_size++] = t;
 
         return 1;
 }