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>

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;