When dbus client connects to systemd-bus-proxyd through
Unix domain socket proxy takes client's smack label and sets for itself.
It is done before and independent of dropping privileges.
The reason of such soluton is fact that tests of access rights
performed by lsm may take place inside kernel, not only
in userspace of recipient of message.
The bus-proxyd needs CAP_MAC_ADMIN to manipulate its label.
In case of systemd running in system mode, CAP_MAC_ADMIN
should be added to CapabilityBoundingSet in service file of bus-proxyd.
In case of systemd running in user mode ('systemd --user')
it can be achieved by addition
Capabilities=cap_mac_admin=i and SecureBits=keep-caps
to user@.service file
and setting cap_mac_admin+ei on bus-proxyd binary.
Signed-off-by: Przemyslaw Kedzierski <p.kedzier...@samsung.com>
---
src/bus-proxyd/bus-proxyd.c | 16 ++++++++++++++++
src/shared/capability.c | 18 ++++++++++++++++++
src/shared/capability.h | 2 ++
src/shared/smack-util.c | 18 ++++++++++++++++++
src/shared/smack-util.h | 1 +
units/systemd-bus-pro...@.service.in | 2 +-
units/u...@.service.in | 2 ++
7 files changed, 58 insertions(+), 1 deletion(-)
diff --git a/src/bus-proxyd/bus-proxyd.c b/src/bus-proxyd/bus-proxyd.c
index d10de2f..066232e 100644
--- a/src/bus-proxyd/bus-proxyd.c
+++ b/src/bus-proxyd/bus-proxyd.c
@@ -45,6 +45,7 @@
#include "def.h"
#include "capability.h"
#include "bus-policy.h"
+#include "smack-util.h"
static char *arg_address = NULL;
static char *arg_command_line_buffer = NULL;
@@ -1168,6 +1169,21 @@ int main(int argc, char *argv[]) {
if (is_unix) {
(void) getpeercred(in_fd, &ucred);
(void) getpeersec(in_fd, &peersec);
+
+ if (mac_smack_use()) {
+ if (peersec) {
+
+ r = mac_smack_set_process_label(peersec);
+ if (r < 0)
+ log_warning("Failed to set SMACK label
%s : %s", peersec, strerror(-r));
+ } else {
+ log_warning("Invalid SMACK label");
+ }
+
+ r = drop_capability(CAP_MAC_ADMIN);
+ if (r < 0)
+ log_warning("Failed to drop CAP_MAC_ADMIN:
%s", strerror(-r));
+ }
}
if (arg_drop_privileges) {
diff --git a/src/shared/capability.c b/src/shared/capability.c
index 0226542..9dc42ec 100644
--- a/src/shared/capability.c
+++ b/src/shared/capability.c
@@ -285,3 +285,21 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t
keep_capabilities) {
return 0;
}
+
+int drop_capability(cap_value_t cv) {
+ _cleanup_cap_free_ cap_t tmp_cap = NULL;
+
+ tmp_cap = cap_get_proc();
+ if (!tmp_cap)
+ return -errno;
+
+ if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
+ (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
+ (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
+ return -errno;
+
+ if (cap_set_proc(tmp_cap) < 0)
+ return -errno;
+
+ return 0;
+}
diff --git a/src/shared/capability.h b/src/shared/capability.h
index 3e6d999..6f2f6f9 100644
--- a/src/shared/capability.h
+++ b/src/shared/capability.h
@@ -34,6 +34,8 @@ int capability_bounding_set_drop_usermode(uint64_t drop);
int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilites);
+int drop_capability(cap_value_t cv);
+
DEFINE_TRIVIAL_CLEANUP_FUNC(cap_t, cap_free);
#define _cleanup_cap_free_ _cleanup_(cap_freep)
diff --git a/src/shared/smack-util.c b/src/shared/smack-util.c
index a8dccd1..3e9810c 100644
--- a/src/shared/smack-util.c
+++ b/src/shared/smack-util.c
@@ -181,3 +181,21 @@ int mac_smack_fix(const char *path, bool ignore_enoent,
bool ignore_erofs) {
return r;
}
+
+int mac_smack_set_process_label(char *label) {
+#ifdef HAVE_SMACK
+ int ret;
+
+ if (!label) {
+ log_debug("No SMACK label given");
+ return -1;
+ }
+ ret = write_string_file("/proc/self/attr/current", label);
+ if (ret) {
+ log_debug("Failed to set current SMACK label \"%s\" on self:
%s",
+ label, strerror(-ret));
+ return ret;
+ }
+#endif
+ return 0;
+}
diff --git a/src/shared/smack-util.h b/src/shared/smack-util.h
index 68778da..a49405b 100644
--- a/src/shared/smack-util.h
+++ b/src/shared/smack-util.h
@@ -33,3 +33,4 @@ int mac_smack_apply(const char *path, const char *label);
int mac_smack_apply_fd(int fd, const char *label);
int mac_smack_apply_ip_in_fd(int fd, const char *label);
int mac_smack_apply_ip_out_fd(int fd, const char *label);
+int mac_smack_set_process_label(char *label);
diff --git a/units/systemd-bus-pro...@.service.in
b/units/systemd-bus-pro...@.service.in
index eef703f..654bfb2 100644
--- a/units/systemd-bus-pro...@.service.in
+++ b/units/systemd-bus-pro...@.service.in
@@ -14,7 +14,7 @@ Description=Legacy D-Bus Protocol Compatibility Daemon
# space available for this.
ExecStart=@rootlibexecdir@/systemd-bus-proxyd --drop-privileges
--address=kernel:path=/dev/kdbus/0-system/bus
--configuration=/etc/dbus-1/system.conf
--configuration=/etc/dbus-1/system-local.conf
--configuration=/etc/dbus-1/system.d/ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
NotifyAccess=main
-CapabilityBoundingSet=CAP_IPC_OWNER CAP_SETUID CAP_SETGID CAP_SETPCAP
+CapabilityBoundingSet=CAP_IPC_OWNER CAP_SETUID CAP_SETGID CAP_SETPCAP
CAP_MAC_ADMIN
PrivateTmp=yes
PrivateDevices=yes
PrivateNetwork=yes
diff --git a/units/u...@.service.in b/units/u...@.service.in
index 8091ce1..9c0903e 100644
--- a/units/u...@.service.in
+++ b/units/u...@.service.in
@@ -16,3 +16,5 @@ Type=notify
ExecStart=-@rootlibexecdir@/systemd --user
Slice=user-%i.slice
KillMode=mixed
+Capabilities=cap_mac_admin=i
+SecureBits=keep-caps
--
2.1.2
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