SO_PEERSEC on socket connected to the same process

[Laurent Bigonville <bigon@xxxxxxxxxx>]

Hi,

Currently the dbus-daemon is not returning anything when asked about its 
own security context (using GetConnectionSELinuxSecurityContext or 
GetConnectionCredentials methods). This cause some issues[0] with 
systemd now that it's enforcing the policy for user sessions again.

I already made a patch that has been merged[1][2] upstream in the 
GetConnectionSELinuxSecurityContext case and it now returns the SELinux 
context of the dbus-daemon process itself.

For the GetConnectionCredentials case, upstream wanted a generic way of 
getting the security label and went the way of using SO_PEERSEC on a 
socket connected to itself.

But for some reasons it's always returning unlabeled_t. Note that the 
same value is returned by the getpeercon() function as well.

I've made a small test case (see attached file) and tested it on both 
debian and RHEL7.

Is this somehow expected? Is this a bug?

Cheers,

Laurent Bigonville

[0]https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=864221
[1]https://bugs.freedesktop.org/show_bug.cgi?id=101315
[2] https://phabricator.freedesktop.org/rDBUSdcf02f80656d

#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>
#include <selinux/selinux.h>

int main(void) {

	int socks[2];
	char buf[1024] = "";
	int len = sizeof(buf);
	char *context = NULL;

	if (getcon_raw(&context) < 0)
		perror("getcon_raw");
	printf("getcon: %s\n", context);
	freecon(context);

	if (socketpair (AF_UNIX, SOCK_STREAM, 0, socks) < 0)
		perror("socketpair");

	if (getsockopt (socks[0], SOL_SOCKET, SO_PEERSEC, &buf, &len) < 0)
		perror("getsockopt 1");
	printf("socket 1: %s\n", buf);

	len = sizeof(buf);

	if (getsockopt (socks[1], SOL_SOCKET, SO_PEERSEC, &buf, &len) < 0)
		perror("getsockopt 2");
	printf("socket 2: %s\n", buf);

	if (getpeercon_raw(socks[0], &context) < 0)
		perror("getpeercon_raw 1");
	printf("getpeercon 1: %s\n", context);
	freecon(context);

	if (getpeercon_raw(socks[1], &context) < 0)
		perror("getpeercon_raw 2");
	printf("getpeercon 2: %s\n", context);
	freecon(context);

	close(socks[0]);
	close(socks[1]);


	return 0;
}