From 2dc9970bed3cee69e6746b110a649a9285dd6369 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Tue, 24 Dec 2013 16:20:47 +0100
Subject: [PATCH] bus: only accept kdbus creds if they are valid

This allows userspace to fake kdbus creds via struct ucred in the proxy,
without making the recieving side choke on the missing fields of the
kdbus struct, more precisel pid_starttime and tid
---
 src/libsystemd-bus/bus-control.c | 16 ++++++++++++----
 src/libsystemd-bus/bus-kernel.c  | 21 ++++++++++++++++++---
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/src/libsystemd-bus/bus-control.c b/src/libsystemd-bus/bus-control.c
index 1eed7b9e320..55986f349b4 100644
--- a/src/libsystemd-bus/bus-control.c
+++ b/src/libsystemd-bus/bus-control.c
@@ -407,17 +407,25 @@ static int bus_get_owner_kdbus(
                 switch (item->type) {
 
                 case KDBUS_ITEM_CREDS:
-                        m = (SD_BUS_CREDS_UID | SD_BUS_CREDS_GID | SD_BUS_CREDS_PID |
-                             SD_BUS_CREDS_TID | SD_BUS_CREDS_PID_STARTTIME) & mask;
+                        m = (SD_BUS_CREDS_UID | SD_BUS_CREDS_GID | SD_BUS_CREDS_PID) & mask;
 
                         if (m) {
                                 c->uid = item->creds.uid;
                                 c->pid = item->creds.pid;
                                 c->gid = item->creds.gid;
-                                c->tid = item->creds.tid;
-                                c->pid_starttime = item->creds.starttime;
                                 c->mask |= m;
                         }
+
+                        if (mask & SD_BUS_CREDS_TID && item->creds.tid > 0) {
+                                c->tid = item->creds.tid;
+                                c->mask |= SD_BUS_CREDS_TID;
+                        }
+
+                        if (mask & SD_BUS_CREDS_PID_STARTTIME && item->creds.starttime > 0) {
+                                c->pid_starttime = item->creds.starttime;
+                                c->mask |= SD_BUS_CREDS_PID_STARTTIME;
+                        }
+
                         break;
 
                 case KDBUS_ITEM_PID_COMM:
diff --git a/src/libsystemd-bus/bus-kernel.c b/src/libsystemd-bus/bus-kernel.c
index 05544e1e477..19d97b7e001 100644
--- a/src/libsystemd-bus/bus-kernel.c
+++ b/src/libsystemd-bus/bus-kernel.c
@@ -793,12 +793,27 @@ static int bus_kernel_make_message(sd_bus *bus, struct kdbus_msg *k) {
                 }
 
                 case KDBUS_ITEM_CREDS:
-                        m->creds.pid_starttime = d->creds.starttime / NSEC_PER_USEC;
+                        /* UID/GID/PID are always valid */
                         m->creds.uid = d->creds.uid;
                         m->creds.gid = d->creds.gid;
                         m->creds.pid = d->creds.pid;
-                        m->creds.tid = d->creds.tid;
-                        m->creds.mask |= (SD_BUS_CREDS_UID|SD_BUS_CREDS_GID|SD_BUS_CREDS_PID|SD_BUS_CREDS_PID_STARTTIME|SD_BUS_CREDS_TID) & bus->creds_mask;
+                        m->creds.mask |= (SD_BUS_CREDS_UID|SD_BUS_CREDS_GID|SD_BUS_CREDS_PID) & bus->creds_mask;
+
+                        /* The PID starttime/TID might be missing
+                         * however, when the data is faked by some
+                         * data bus proxy and it lacks that
+                         * information about the real client since
+                         * SO_PEERCRED is used for that */
+
+                        if (d->creds.starttime > 0) {
+                                m->creds.pid_starttime = d->creds.starttime / NSEC_PER_USEC;
+                                m->creds.mask |= SD_BUS_CREDS_PID_STARTTIME & bus->creds_mask;
+                        }
+
+                        if (d->creds.tid > 0) {
+                                m->creds.tid = d->creds.tid;
+                                m->creds.mask |= SD_BUS_CREDS_TID & bus->creds_mask;
+                        }
                         break;
 
                 case KDBUS_ITEM_TIMESTAMP: