bus: use EUID over UID and fix unix-creds

Whenever a process performs an action on an object, the kernel uses the
EUID of the process to do permission checks and to apply on any newly
created objects. The UID of a process is only used if someone *ELSE* acts
on the process. That is, the UID of a process defines who owns the
process, the EUID defines what privileges are used by this process when
performing an action.

Process limits, on the other hand, are always applied to the real UID, not
the effective UID. This is, because a process has a user object linked,
which always corresponds to its UID. A process never has a user object
linked for its EUID. Thus, accounting (and limits) is always done on the
real UID.

This commit fixes all sd-bus users to use the EUID when performing
privilege checks and alike. Furthermore, it fixes unix-creds to be parsed
as EUID, not UID (as the kernel always takes the EUID on UDS). Anyone
using UID (eg., to do user-accounting) has to fall back to the EUID as UDS
does not transmit the UID.

3 files changed, 16 insertions, 16 deletions

diff --git a/src/libsystemd/sd-bus/bus-control.c b/src/libsystemd/sd-bus/bus-control.c
index b45014078d..35c79cf899 100644
--- a/src/libsystemd/sd-bus/bus-control.c
+++ b/src/libsystemd/sd-bus/bus-control.c
@@ -762,7 +762,7 @@ static int bus_get_name_creds_dbus1(
 
                 if ((mask & SD_BUS_CREDS_PID) ||
                     ((mask & SD_BUS_CREDS_AUGMENT) &&
-                     (mask & (SD_BUS_CREDS_EUID|SD_BUS_CREDS_SUID|SD_BUS_CREDS_FSUID|
+                     (mask & (SD_BUS_CREDS_UID|SD_BUS_CREDS_SUID|SD_BUS_CREDS_FSUID|
                               SD_BUS_CREDS_GID|SD_BUS_CREDS_EGID|SD_BUS_CREDS_SGID|SD_BUS_CREDS_FSGID|
                               SD_BUS_CREDS_COMM|SD_BUS_CREDS_EXE|SD_BUS_CREDS_CMDLINE|
                               SD_BUS_CREDS_CGROUP|SD_BUS_CREDS_UNIT|SD_BUS_CREDS_USER_UNIT|SD_BUS_CREDS_SLICE|SD_BUS_CREDS_SESSION|SD_BUS_CREDS_OWNER_UID|
@@ -798,7 +798,7 @@ static int bus_get_name_creds_dbus1(
                         reply = sd_bus_message_unref(reply);
                 }
 
-                if (mask & SD_BUS_CREDS_UID) {
+                if (mask & SD_BUS_CREDS_EUID) {
                         uint32_t u;
 
                         r = sd_bus_call_method(
@@ -818,8 +818,8 @@ static int bus_get_name_creds_dbus1(
                         if (r < 0)
                                 return r;
 
-                        c->uid = u;
-                        c->mask |= SD_BUS_CREDS_UID;
+                        c->euid = u;
+                        c->mask |= SD_BUS_CREDS_EUID;
 
                         reply = sd_bus_message_unref(reply);
                 }
@@ -961,13 +961,13 @@ static int bus_get_owner_creds_dbus1(sd_bus *bus, uint64_t mask, sd_bus_creds **
                 }
 
                 if (bus->ucred.uid != UID_INVALID) {
-                        c->uid = bus->ucred.uid;
-                        c->mask |= SD_BUS_CREDS_UID & mask;
+                        c->euid = bus->ucred.uid;
+                        c->mask |= SD_BUS_CREDS_EUID & mask;
                 }
 
                 if (bus->ucred.gid != GID_INVALID) {
-                        c->gid = bus->ucred.gid;
-                        c->mask |= SD_BUS_CREDS_GID & mask;
+                        c->egid = bus->ucred.gid;
+                        c->mask |= SD_BUS_CREDS_EGID & mask;
                 }
         }
 
diff --git a/src/libsystemd/sd-bus/bus-message.c b/src/libsystemd/sd-bus/bus-message.c
index f352c72981..23076d25dd 100644
--- a/src/libsystemd/sd-bus/bus-message.c
+++ b/src/libsystemd/sd-bus/bus-message.c
@@ -424,19 +424,19 @@ int bus_message_from_header(
 
         if (ucred) {
                 m->creds.pid = ucred->pid;
-                m->creds.uid = ucred->uid;
-                m->creds.gid = ucred->gid;
+                m->creds.euid = ucred->uid;
+                m->creds.egid = ucred->gid;
 
                 /* Due to namespace translations some data might be
                  * missing from this ucred record. */
                 if (m->creds.pid > 0)
                         m->creds.mask |= SD_BUS_CREDS_PID;
 
-                if (m->creds.uid != UID_INVALID)
-                        m->creds.mask |= SD_BUS_CREDS_UID;
+                if (m->creds.euid != UID_INVALID)
+                        m->creds.mask |= SD_BUS_CREDS_EUID;
 
-                if (m->creds.gid != GID_INVALID)
-                        m->creds.mask |= SD_BUS_CREDS_GID;
+                if (m->creds.egid != GID_INVALID)
+                        m->creds.mask |= SD_BUS_CREDS_EGID;
         }
 
         if (label) {
diff --git a/src/libsystemd/sd-bus/busctl.c b/src/libsystemd/sd-bus/busctl.c
index c0d51e06a3..f0bc2a76a5 100644
--- a/src/libsystemd/sd-bus/busctl.c
+++ b/src/libsystemd/sd-bus/busctl.c
@@ -160,7 +160,7 @@ static int list_bus_names(sd_bus *bus, char **argv) {
                 r = sd_bus_get_name_creds(
                                 bus, *i,
                                 (arg_augment_creds ? SD_BUS_CREDS_AUGMENT : 0) |
-                                SD_BUS_CREDS_UID|SD_BUS_CREDS_PID|SD_BUS_CREDS_COMM|
+                                SD_BUS_CREDS_EUID|SD_BUS_CREDS_PID|SD_BUS_CREDS_COMM|
                                 SD_BUS_CREDS_UNIQUE_NAME|SD_BUS_CREDS_UNIT|SD_BUS_CREDS_SESSION|
                                 SD_BUS_CREDS_DESCRIPTION, &creds);
                 if (r >= 0) {
@@ -178,7 +178,7 @@ static int list_bus_names(sd_bus *bus, char **argv) {
                         } else
                                 fputs("          - -              ", stdout);
 
-                        r = sd_bus_creds_get_uid(creds, &uid);
+                        r = sd_bus_creds_get_euid(creds, &uid);
                         if (r >= 0) {
                                 _cleanup_free_ char *u = NULL;