Test to trace NFS unlabeled bug

[Richard Haines <richard_c_haines@xxxxxxxxxxxxxx>]

I've been building selinux-testsuite tests for various filesystems and
have come across an unlabeled issue when testing. Stephen thinks that
this is a bug sometimes seen with labeled NFS, where the top-level
mounted directory shows up with unlabeled_t initially, then later gets
refreshed to a valid context.

I've put together a test script, policy module and mount prog to
facilitate debugging this issue. I've set out how I tested this on a
Fedora 31 system below, if any problems let me know. 

The nfs.sh script:
MOUNT=`stat --print %m .`
TESTDIR=`pwd`
systemctl start nfs-server
exportfs -orw,no_root_squash,security_label localhost:$MOUNT
mkdir -p /mnt/selinux-testsuite
runcon -t test_nfs_unlabeled_bug ./mount -f nfs4 -s localhost:$TESTDIR
-t /mnt/selinux-testsuite -o
"nfsvers=4.2,proto=tcp,clientaddr=127.0.0.1,addr=127.0.0.1" -v
umount /mnt/selinux-testsuite
exportfs -u localhost:$MOUNT
systemctl stop nfs-server

Install mount.c, unlabeled_bug.te and nfs.sh

Build mount prog:
cc mount.c -o mount -Wall
Then:
chcon -t bin_t ./mount

Build policy module and install:
make -f /usr/share/selinux/devel/Makefile unlabeled_bug.pp
semodule -i unlabeled_bug.pp

Clean audit log:
> /var/log/audit/audit.log

run ./nfs.sh

Check audit log:
audit2allow -p /etc/selinux/targeted/policy/policy.31 <
/var/log/audit/audit.log

Should see:
#============= test_nfs_unlabeled_bug ==============
allow test_nfs_unlabeled_bug unlabeled_t:dir search;

Once done:
semodule -r unlabeled_bug

/* cc mount.c -o mount -Wall */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdbool.h>
#include <sys/mount.h>

static void print_usage(char *progname)
{
	fprintf(stderr,
		"usage:  %s [-s src] -t tgt [-f fs_type] [-o options]\n"
		"Where:\n\t"
		"-s  Source path\n\t"
		"-t  Target path\n\t"
		"-f  Filesystem type\n\t"
		"-o  Options list (comma separated list)\n\t"
		"-v  Print information.\n", progname);
	exit(-1);
}

int main(int argc, char *argv[])
{
	int opt, result, save_err, flags = 0;
	char *src = NULL, *tgt = NULL, *fs_type = NULL, *opts = NULL;
	bool verbose = false;

	while ((opt = getopt(argc, argv, "s:t:f:o:v")) != -1) {
		switch (opt) {
		case 's':
			src = optarg;
			break;
		case 't':
			tgt = optarg;
			break;
		case 'f':
			fs_type = optarg;
			break;
		case 'o':
			opts = optarg;
			break;
		case 'v':
			verbose = true;
			break;
		default:
			print_usage(argv[0]);
		}
	}

	if (!tgt)
		print_usage(argv[0]);

	if (verbose)
		printf("Mounting\n\tsrc: %s\n\ttgt: %s\n\tfs_type: %s flags: 0x%x\n\topts: %s\n",
		       src, tgt, fs_type, flags, opts);

	result = mount(src, tgt, fs_type, flags, opts);
	save_err = errno;
	if (result < 0) {
		fprintf(stderr, "Failed mount(2): %s\n", strerror(errno));
		return save_err;
	}

	return 0;
}

Attachment: test-nfs.sh
Description: application/shellscript

policy_module(unlabeled_bug, 1.0)

require {
	role unconfined_r;
	type bin_t,user_devpts_t,nfs_t,kernel_t;
	class file { entrypoint execute read };
	class capability { sys_admin };
	class system { module_request };
	class chr_file { append getattr read write };
	class dir { search };
	class filesystem { mount };
}

#============= test_nfs_unlabeled_bug ==============
type test_nfs_unlabeled_bug;
role unconfined_r types test_nfs_unlabeled_bug;
files_type(test_nfs_unlabeled_bug)
domain_type(test_nfs_unlabeled_bug)
allow test_nfs_unlabeled_bug bin_t:file { entrypoint execute read };
files_mounton_default(test_nfs_unlabeled_bug)
allow test_nfs_unlabeled_bug bin_t:file map;
allow test_nfs_unlabeled_bug default_t:dir mounton;
allow test_nfs_unlabeled_bug self:capability sys_admin;
allow test_nfs_unlabeled_bug kernel_t:system module_request;
allow test_nfs_unlabeled_bug nfs_t:dir search;
allow test_nfs_unlabeled_bug nfs_t:filesystem mount;
allow test_nfs_unlabeled_bug user_devpts_t:chr_file { append getattr read write };

#allow test_nfs_unlabeled_bug unlabeled_t:dir search;