socket: introduce SELinuxLabelViaNet option

This makes possible to spawn service instances triggered by socket with
MLS/MCS SELinux labels which are created based on information provided by
connected peer.

Implementation of label_get_child_label derived from xinetd.

Reviewed-by: Paul Moore <pmoore@redhat.com>

man/systemd.socket.xml

@@ -675,6 +675,17 @@
                                 for details.</para></listitem>
                         </varlistentry>
 
+                        <varlistentry>
+                          <term><varname>SELinuxLabelViaNet=</varname></term>
+                          <listitem><para>Takes a boolean
+                          value. Controls whether systemd attempts to figure out
+                          SELinux label used for instantiated service from
+                          information handed by peer over the
+                          network. Configuration option has effect only
+                          on sockets with <literal>Accept=</literal>
+                          mode set to <literal>yes</literal>.</para></listitem>
+                        </varlistentry>
+
                         <varlistentry>
                                 <term><varname>PipeSize=</varname></term>
                                 <listitem><para>Takes a size in

src/core/execute.c

@@ -83,6 +83,7 @@
 #include "af-list.h"
 #include "mkdir.h"
 #include "apparmor-util.h"
+#include "label.h"
 
 #ifdef HAVE_SECCOMP
 #include "seccomp-util.h"
@@ -1729,6 +1730,22 @@ int exec_spawn(ExecCommand *command,
                                         goto fail_child;
                                 }
                         }
+
+                        if (context->selinux_label_via_net && use_selinux()) {
+                                _cleanup_free_ char *label = NULL;
+
+                                err = label_get_child_label(socket_fd, command->path, &label);
+                                if (err < 0) {
+                                        r = EXIT_SELINUX_CONTEXT;
+                                        goto fail_child;
+                                }
+
+                                err = setexeccon(label);
+                                if (err < 0) {
+                                        r = EXIT_SELINUX_CONTEXT;
+                                        goto fail_child;
+                                }
+                        }
 #endif
 
 #ifdef HAVE_APPARMOR
@@ -2112,7 +2129,8 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
                 "%sPrivateDevices: %s\n"
                 "%sProtectHome: %s\n"
                 "%sProtectSystem: %s\n"
-                "%sIgnoreSIGPIPE: %s\n",
+                "%sIgnoreSIGPIPE: %s\n"
+                "%sSELinuxLabelViaNet: %s\n",
                 prefix, c->umask,
                 prefix, c->working_directory ? c->working_directory : "/",
                 prefix, c->root_directory ? c->root_directory : "/",
@@ -2122,7 +2140,8 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
                 prefix, yes_no(c->private_devices),
                 prefix, protect_home_to_string(c->protect_home),
                 prefix, protect_system_to_string(c->protect_system),
-                prefix, yes_no(c->ignore_sigpipe));
+                prefix, yes_no(c->ignore_sigpipe),
+                prefix, yes_no(c->selinux_label_via_net));
 
         STRV_FOREACH(e, c->environment)
                 fprintf(f, "%sEnvironment: %s\n", prefix, *e);

src/core/execute.h

@@ -136,6 +136,7 @@ struct ExecContext {
 
         bool selinux_context_ignore;
         char *selinux_context;
+        bool selinux_label_via_net;
 
         bool apparmor_profile_ignore;
         char *apparmor_profile;

src/core/load-fragment-gperf.gperf.m4

@@ -262,6 +262,9 @@ Socket.SmackLabelIPOut,          config_parse_string,                0,
 `Socket.SmackLabel,              config_parse_warn_compat,           0,                             0
 Socket.SmackLabelIPIn,           config_parse_warn_compat,           0,                             0
 Socket.SmackLabelIPOut,          config_parse_warn_compat,           0,                             0')
+m4_ifdef(`HAVE_SELINUX',
+`Socket.SELinuxLabelViaNet,      config_parse_bool,                  0,                             offsetof(Socket, selinux_label_via_net)',
+`Socket.SELinuxLabelViaNet,      config_parse_warn_compat,           0,                             0')
 EXEC_CONTEXT_CONFIG_ITEMS(Socket)m4_dnl
 CGROUP_CONTEXT_CONFIG_ITEMS(Socket)m4_dnl
 KILL_CONTEXT_CONFIG_ITEMS(Socket)m4_dnl

src/core/socket.c

@@ -31,6 +31,10 @@
 #include <mqueue.h>
 #include <sys/xattr.h>
 
+#ifdef HAVE_SELINUX
+#include <selinux/selinux.h>
+#endif
+
 #include "sd-event.h"
 #include "log.h"
 #include "load-dropin.h"
@@ -488,7 +492,8 @@ static void socket_dump(Unit *u, FILE *f, const char *prefix) {
                 "%sPassCredentials: %s\n"
                 "%sPassSecurity: %s\n"
                 "%sTCPCongestion: %s\n"
-                "%sRemoveOnStop: %s\n",
+                "%sRemoveOnStop: %s\n"
+                "%sSELinuxLabelViaNet: %s\n",
                 prefix, socket_state_to_string(s->state),
                 prefix, socket_result_to_string(s->result),
                 prefix, socket_address_bind_ipv6_only_to_string(s->bind_ipv6_only),
@@ -503,7 +508,8 @@ static void socket_dump(Unit *u, FILE *f, const char *prefix) {
                 prefix, yes_no(s->pass_cred),
                 prefix, yes_no(s->pass_sec),
                 prefix, strna(s->tcp_congestion),
-                prefix, yes_no(s->remove_on_stop));
+                prefix, yes_no(s->remove_on_stop),
+                prefix, yes_no(s->selinux_label_via_net));
 
         if (s->control_pid > 0)
                 fprintf(f,
@@ -1130,7 +1136,14 @@ static int socket_open_fds(Socket *s) {
                         continue;
 
                 if (p->type == SOCKET_SOCKET) {
-
+#ifdef HAVE_SELINUX
+                        if (!know_label && s->selinux_label_via_net) {
+                                r = getcon(&label);
+                                if (r < 0)
+                                        return r;
+                                know_label = true;
+                        }
+#endif
                         if (!know_label) {
 
                                 r = socket_instantiate_service(s);
@@ -1829,6 +1842,9 @@ static void socket_enter_running(Socket *s, int cfd) {
                 cfd = -1;
                 s->n_connections ++;
 
+                if (s->selinux_label_via_net)
+                        service->exec_context.selinux_label_via_net = true;
+
                 r = manager_add_job(UNIT(s)->manager, JOB_START, UNIT(service), JOB_REPLACE, true, &error, NULL);
                 if (r < 0)
                         goto fail;

src/core/socket.h

@@ -165,6 +165,8 @@ struct Socket {
         char *smack_ip_in;
         char *smack_ip_out;
 
+        bool selinux_label_via_net;
+
         char *user, *group;
 };
 

src/shared/label.c

@@ -31,6 +31,7 @@
 #ifdef HAVE_SELINUX
 #include <selinux/selinux.h>
 #include <selinux/label.h>
+#include <selinux/context.h>
 #endif
 
 #include "label.h"
@@ -243,6 +244,74 @@ fail:
         return r;
 }
 
+int label_get_child_label(int socket_fd, const char *exe, char **label) {
+        int r = 0;
+
+#ifdef HAVE_SELINUX
+
+        security_context_t mycon = NULL, peercon = NULL, fcon = NULL, ret = NULL;
+        security_class_t sclass;
+        context_t pcon = NULL, bcon = NULL;
+        const char *range = NULL;
+
+        assert(socket_fd >= 0);
+        assert(exe);
+        assert(label);
+
+        r = getcon(&mycon);
+        if (r < 0)
+                goto out;
+
+        r = getpeercon(socket_fd, &peercon);
+        if (r < 0)
+                goto out;
+
+        r = getfilecon(exe, &fcon);
+        if (r < 0)
+                goto out;
+
+        bcon = context_new(mycon);
+        if (!bcon)
+                goto out;
+
+        pcon = context_new(peercon);
+        if (!pcon)
+                goto out;
+
+        range = context_range_get(pcon);
+        if (!range)
+                goto out;
+
+        r = context_range_set(bcon, range);
+        if (r)
+                goto out;
+
+        freecon(mycon);
+        mycon = context_str(bcon);
+        if (!mycon)
+                goto out;
+
+        sclass = string_to_security_class("process");
+        r = security_compute_create(mycon, fcon, sclass, &ret);
+        if (r < 0)
+                goto out;
+
+        *label = ret;
+
+out:
+        if (r && security_getenforce() == 1)
+                r = -errno;
+
+        freecon(mycon);
+        freecon(peercon);
+        freecon(fcon);
+        context_free(pcon);
+        context_free(bcon);
+
+#endif
+        return r;
+}
+
 int label_context_set(const char *path, mode_t mode) {
         int r = 0;
 

src/shared/label.h

@@ -39,6 +39,7 @@ void label_context_clear(void);
 void label_free(const char *label);
 
 int label_get_create_label_from_exe(const char *exe, char **label);
+int label_get_child_label(int socket_fd, const char *exec, char **label);
 
 int label_mkdir(const char *path, mode_t mode);