LSM: SafeSetID: add selftest
diff mbox series

Message ID 20190206190309.247032-1-mortonm@chromium.org
State New
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Series
  • LSM: SafeSetID: add selftest
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Commit Message

Micah Morton Feb. 6, 2019, 7:03 p.m. UTC
From: Micah Morton <mortonm@chromium.org>

This patch adds a selftest for the SafeSetID LSM. The test requires
mounting securityfs if it isn't mounted, creating test users in
/etc/passwd, and configuring policies for the SafeSetID LSM through
writes to securityfs.

Signed-off-by: Micah Morton <mortonm@chromium.org>
---
This test is reasonably robust for demonstrating the functionality of
the LSM, but is no masterpiece by any means. I'm not totally sure how
these tests are used. Are they incorporated into testing frameworks for
the Linux kernel that are run regularly or just PoC binaries that sit in
this directory more or less as documentation? If its the former, this
code probably needs some more cleanup and better organization. Beyond
coding style, the test doesn't bother to clean up users that were added
in /etc/passwd for testing purposes nor flushes policies that were
configured for the LSM relating to those users. Should it?

 tools/testing/selftests/safesetid/.gitignore  |   1 +
 tools/testing/selftests/safesetid/Makefile    |   8 +
 tools/testing/selftests/safesetid/config      |   2 +
 .../selftests/safesetid/safesetid-test.c      | 334 ++++++++++++++++++
 .../selftests/safesetid/safesetid-test.sh     |  26 ++
 5 files changed, 371 insertions(+)
 create mode 100644 tools/testing/selftests/safesetid/.gitignore
 create mode 100644 tools/testing/selftests/safesetid/Makefile
 create mode 100644 tools/testing/selftests/safesetid/config
 create mode 100644 tools/testing/selftests/safesetid/safesetid-test.c
 create mode 100755 tools/testing/selftests/safesetid/safesetid-test.sh

Comments

Edwin Zimmerman Feb. 6, 2019, 7:26 p.m. UTC | #1
> On Wednesday, February 06, 2019 2:03 PM Micah Morton wrote:
> > This patch adds a selftest for the SafeSetID LSM. The test requires
> > mounting securityfs if it isn't mounted, creating test users in
> > /etc/passwd, and configuring policies for the SafeSetID LSM through
> > writes to securityfs.
> >
> > Signed-off-by: Micah Morton <mortonm@chromium.org>
> > ---
> > This test is reasonably robust for demonstrating the functionality of
> > the LSM, but is no masterpiece by any means. I'm not totally sure how
> > these tests are used. Are they incorporated into testing frameworks for
> > the Linux kernel that are run regularly or just PoC binaries that sit in
> > this directory more or less as documentation? If its the former, this
> > code probably needs some more cleanup and better organization. Beyond
> > coding style, the test doesn't bother to clean up users that were added
> > in /etc/passwd for testing purposes nor flushes policies that were
> > configured for the LSM relating to those users. Should it?
> 
> No good reason to leave the users, so I would suggest cleaning them up.
> All it would take would be several deluser commands
> in safesetid-test.sh.  Very simple.
Micah Morton Feb. 7, 2019, 9:54 p.m. UTC | #2
Yeah, that would be simple, although maybe someone is counting on
those users to exist later. We could create special users on the
system for the purpose of this test that didn't exist before the test
(and delete them afterward), but then there are other setup/cleanup
questions, like:

- Do we unmount securityfs after the test? What if something was
counting on it being mounted or not mounted?
- Do we flush the SafeSetID LSM policies after the test? Note that the
LSM doesn't currently have the functionality to flush individual
policies, so what happens if something was counting on certain
policies (for other users) being configured for the LSM and we flush
those after running our test?

These questions were the reason I was hoping to get more info on the
kind of environment in which these selftests run. If the norm is to
boot up a VM, run one of these tests, then reboot/shutdown, most of
these questions don't need to be answered (we would still probably
want to fix user creation/deletion since that is persistent across
reboots).

On Wed, Feb 6, 2019 at 11:26 AM Edwin Zimmerman <edwin@211mainstreet.net> wrote:
>
> > On Wednesday, February 06, 2019 2:03 PM Micah Morton wrote:
> > > This patch adds a selftest for the SafeSetID LSM. The test requires
> > > mounting securityfs if it isn't mounted, creating test users in
> > > /etc/passwd, and configuring policies for the SafeSetID LSM through
> > > writes to securityfs.
> > >
> > > Signed-off-by: Micah Morton <mortonm@chromium.org>
> > > ---
> > > This test is reasonably robust for demonstrating the functionality of
> > > the LSM, but is no masterpiece by any means. I'm not totally sure how
> > > these tests are used. Are they incorporated into testing frameworks for
> > > the Linux kernel that are run regularly or just PoC binaries that sit in
> > > this directory more or less as documentation? If its the former, this
> > > code probably needs some more cleanup and better organization. Beyond
> > > coding style, the test doesn't bother to clean up users that were added
> > > in /etc/passwd for testing purposes nor flushes policies that were
> > > configured for the LSM relating to those users. Should it?
> >
> > No good reason to leave the users, so I would suggest cleaning them up.
> > All it would take would be several deluser commands
> > in safesetid-test.sh.  Very simple.
>
James Morris Feb. 12, 2019, 7:01 p.m. UTC | #3
On Wed, 6 Feb 2019, mortonm@chromium.org wrote:

> From: Micah Morton <mortonm@chromium.org>
> 
> This patch adds a selftest for the SafeSetID LSM. The test requires
> mounting securityfs if it isn't mounted, creating test users in
> /etc/passwd, and configuring policies for the SafeSetID LSM through
> writes to securityfs.
> 
> Signed-off-by: Micah Morton <mortonm@chromium.org>

Great!

Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git next-general

Patch
diff mbox series

diff --git a/tools/testing/selftests/safesetid/.gitignore b/tools/testing/selftests/safesetid/.gitignore
new file mode 100644
index 000000000000..9c1a629bca01
--- /dev/null
+++ b/tools/testing/selftests/safesetid/.gitignore
@@ -0,0 +1 @@ 
+safesetid-test
diff --git a/tools/testing/selftests/safesetid/Makefile b/tools/testing/selftests/safesetid/Makefile
new file mode 100644
index 000000000000..98da7a504737
--- /dev/null
+++ b/tools/testing/selftests/safesetid/Makefile
@@ -0,0 +1,8 @@ 
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for mount selftests.
+CFLAGS = -Wall -lcap -O2
+
+TEST_PROGS := run_tests.sh
+TEST_GEN_FILES := safesetid-test
+
+include ../lib.mk
diff --git a/tools/testing/selftests/safesetid/config b/tools/testing/selftests/safesetid/config
new file mode 100644
index 000000000000..9d44e5c2e096
--- /dev/null
+++ b/tools/testing/selftests/safesetid/config
@@ -0,0 +1,2 @@ 
+CONFIG_SECURITY=y
+CONFIG_SECURITYFS=y
diff --git a/tools/testing/selftests/safesetid/safesetid-test.c b/tools/testing/selftests/safesetid/safesetid-test.c
new file mode 100644
index 000000000000..892c8e8b1b8b
--- /dev/null
+++ b/tools/testing/selftests/safesetid/safesetid-test.c
@@ -0,0 +1,334 @@ 
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <errno.h>
+#include <pwd.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/capability.h>
+#include <sys/types.h>
+#include <sys/mount.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdarg.h>
+
+#ifndef CLONE_NEWUSER
+# define CLONE_NEWUSER 0x10000000
+#endif
+
+#define ROOT_USER 0
+#define RESTRICTED_PARENT 1
+#define ALLOWED_CHILD1 2
+#define ALLOWED_CHILD2 3
+#define NO_POLICY_USER 4
+
+char* add_whitelist_policy_file = "/sys/kernel/security/safesetid/add_whitelist_policy";
+
+static void die(char *fmt, ...)
+{
+	va_list ap;
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+	exit(EXIT_FAILURE);
+}
+
+static bool vmaybe_write_file(bool enoent_ok, char *filename, char *fmt, va_list ap)
+{
+	char buf[4096];
+	int fd;
+	ssize_t written;
+	int buf_len;
+
+	buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
+	if (buf_len < 0) {
+		printf("vsnprintf failed: %s\n",
+		    strerror(errno));
+		return false;
+	}
+	if (buf_len >= sizeof(buf)) {
+		printf("vsnprintf output truncated\n");
+		return false;
+	}
+
+	fd = open(filename, O_WRONLY);
+	if (fd < 0) {
+		if ((errno == ENOENT) && enoent_ok)
+			return true;
+		return false;
+	}
+	written = write(fd, buf, buf_len);
+	if (written != buf_len) {
+		if (written >= 0) {
+			printf("short write to %s\n", filename);
+			return false;
+		} else {
+			printf("write to %s failed: %s\n",
+				filename, strerror(errno));
+			return false;
+		}
+	}
+	if (close(fd) != 0) {
+		printf("close of %s failed: %s\n",
+			filename, strerror(errno));
+		return false;
+	}
+	return true;
+}
+
+static bool write_file(char *filename, char *fmt, ...)
+{
+	va_list ap;
+	bool ret;
+
+	va_start(ap, fmt);
+	ret = vmaybe_write_file(false, filename, fmt, ap);
+	va_end(ap);
+
+	return ret;
+}
+
+static void ensure_user_exists(uid_t uid)
+{
+	struct passwd p;
+
+	FILE *fd;
+	char name_str[10];
+
+	if (getpwuid(uid) == NULL) {
+		memset(&p,0x00,sizeof(p));
+		fd=fopen("/etc/passwd","a");
+		if (fd == NULL)
+			die("couldn't open file\n");
+		if (fseek(fd, 0, SEEK_END))
+			die("couldn't fseek\n");
+		snprintf(name_str, 10, "%d", uid);
+		p.pw_name=name_str;
+		p.pw_uid=uid;
+		p.pw_gecos="Test account";
+		p.pw_dir="/dev/null";
+		p.pw_shell="/bin/false";
+		int value = putpwent(&p,fd);
+		if (value != 0)
+			die("putpwent failed\n");
+		if (fclose(fd))
+			die("fclose failed\n");
+	}
+}
+
+static void ensure_securityfs_mounted(void)
+{
+	int fd = open(add_whitelist_policy_file, O_WRONLY);
+	if (fd < 0) {
+		if (errno == ENOENT) {
+			// Need to mount securityfs
+			if (mount("securityfs", "/sys/kernel/security",
+						"securityfs", 0, NULL) < 0)
+				die("mounting securityfs failed\n");
+		} else {
+			die("couldn't find securityfs for unknown reason\n");
+		}
+	} else {
+		if (close(fd) != 0) {
+			die("close of %s failed: %s\n",
+				add_whitelist_policy_file, strerror(errno));
+		}
+	}
+}
+
+static void write_policies(void)
+{
+	ssize_t written;
+	int fd;
+
+	fd = open(add_whitelist_policy_file, O_WRONLY);
+	if (fd < 0)
+		die("cant open add_whitelist_policy file\n");
+	written = write(fd, "1:2", strlen("1:2"));
+	if (written != strlen("1:2")) {
+		if (written >= 0) {
+			die("short write to %s\n", add_whitelist_policy_file);
+		} else {
+			die("write to %s failed: %s\n",
+				add_whitelist_policy_file, strerror(errno));
+		}
+	}
+	written = write(fd, "1:3", strlen("1:3"));
+	if (written != strlen("1:3")) {
+		if (written >= 0) {
+			die("short write to %s\n", add_whitelist_policy_file);
+		} else {
+			die("write to %s failed: %s\n",
+				add_whitelist_policy_file, strerror(errno));
+		}
+	}
+	if (close(fd) != 0) {
+		die("close of %s failed: %s\n",
+			add_whitelist_policy_file, strerror(errno));
+	}
+}
+
+static bool test_userns(bool expect_success)
+{
+	uid_t uid;
+	char map_file_name[32];
+	size_t sz = sizeof(map_file_name);
+	pid_t cpid;
+	bool success;
+
+	uid = getuid();
+
+	int clone_flags = CLONE_NEWUSER;
+	cpid = syscall(SYS_clone, clone_flags, NULL);
+	if (cpid == -1) {
+	    printf("clone failed");
+	    return false;
+	}
+
+	if (cpid == 0) {	/* Code executed by child */
+		// Give parent 1 second to write map file
+		sleep(1);
+		exit(EXIT_SUCCESS);
+	} else {		/* Code executed by parent */
+		if(snprintf(map_file_name, sz, "/proc/%d/uid_map", cpid) < 0) {
+			printf("preparing file name string failed");
+			return false;
+		}
+		success = write_file(map_file_name, "0 0 1", uid);
+		return success == expect_success;
+	}
+
+	printf("should not reach here");
+	return false;
+}
+
+static void test_setuid(uid_t child_uid, bool expect_success)
+{
+	pid_t cpid, w;
+	int wstatus;
+
+	cpid = fork();
+	if (cpid == -1) {
+		die("fork\n");
+	}
+
+	if (cpid == 0) {	    /* Code executed by child */
+		setuid(child_uid);
+		if (getuid() == child_uid)
+			exit(EXIT_SUCCESS);
+		else
+			exit(EXIT_FAILURE);
+	} else {		 /* Code executed by parent */
+		do {
+			w = waitpid(cpid, &wstatus, WUNTRACED | WCONTINUED);
+			if (w == -1) {
+				die("waitpid\n");
+			}
+
+			if (WIFEXITED(wstatus)) {
+				if (WEXITSTATUS(wstatus) == EXIT_SUCCESS) {
+					if (expect_success) {
+						return;
+					} else {
+						die("unexpected success\n");
+					}
+				} else {
+					if (expect_success) {
+						die("unexpected failure\n");
+					} else {
+						return;
+					}
+				}
+			} else if (WIFSIGNALED(wstatus)) {
+				if (WTERMSIG(wstatus) == 9) {
+					if (expect_success)
+						die("killed unexpectedly\n");
+					else
+						return;
+				} else {
+					die("unexpected signal: %d\n", wstatus);
+				}
+			} else {
+				die("unexpected status: %d\n", wstatus);
+			}
+		} while (!WIFEXITED(wstatus) && !WIFSIGNALED(wstatus));
+	}
+
+	die("should not reach here\n");
+}
+
+static void ensure_users_exist(void)
+{
+	ensure_user_exists(ROOT_USER);
+	ensure_user_exists(RESTRICTED_PARENT);
+	ensure_user_exists(ALLOWED_CHILD1);
+	ensure_user_exists(ALLOWED_CHILD2);
+	ensure_user_exists(NO_POLICY_USER);
+}
+
+static void drop_caps(bool setid_retained)
+{
+	cap_value_t cap_values[] = {CAP_SETUID, CAP_SETGID};
+	cap_t caps;
+
+	caps = cap_get_proc();
+	if (setid_retained)
+		cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_values, CAP_SET);
+	else
+		cap_clear(caps);
+	cap_set_proc(caps);
+	cap_free(caps);
+}
+
+int main(int argc, char **argv)
+{
+	ensure_users_exist();
+	ensure_securityfs_mounted();
+	write_policies();
+
+	if (prctl(PR_SET_KEEPCAPS, 1L))
+		die("Error with set keepcaps\n");
+
+	// First test to make sure we can write userns mappings from a user
+	// that doesn't have any restrictions (as long as it has CAP_SETUID);
+	setuid(NO_POLICY_USER);
+	setgid(NO_POLICY_USER);
+
+	// Take away all but setid caps
+	drop_caps(true);
+
+	// Need PR_SET_DUMPABLE flag set so we can write /proc/[pid]/uid_map
+	// from non-root parent process.
+	if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0))
+		die("Error with set dumpable\n");
+
+	if (!test_userns(true)) {
+		die("test_userns failed when it should work\n");
+	}
+
+	setuid(RESTRICTED_PARENT);
+	setgid(RESTRICTED_PARENT);
+
+	test_setuid(ROOT_USER, false);
+	test_setuid(ALLOWED_CHILD1, true);
+	test_setuid(ALLOWED_CHILD2, true);
+	test_setuid(NO_POLICY_USER, false);
+
+	if (!test_userns(false)) {
+		die("test_userns worked when it should fail\n");
+	}
+
+	// Now take away all caps
+	drop_caps(false);
+	test_setuid(2, false);
+	test_setuid(3, false);
+	test_setuid(4, false);
+
+	// NOTE: this test doesn't clean up users that were created in
+	// /etc/passwd or flush policies that were added to the LSM.
+	return EXIT_SUCCESS;
+}
diff --git a/tools/testing/selftests/safesetid/safesetid-test.sh b/tools/testing/selftests/safesetid/safesetid-test.sh
new file mode 100755
index 000000000000..e4fdce675c54
--- /dev/null
+++ b/tools/testing/selftests/safesetid/safesetid-test.sh
@@ -0,0 +1,26 @@ 
+#!/bin/bash
+
+TCID="safesetid-test.sh"
+errcode=0
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+check_root()
+{
+	uid=$(id -u)
+	if [ $uid -ne 0 ]; then
+		echo $TCID: must be run as root >&2
+		exit $ksft_skip
+	fi
+}
+
+main_function()
+{
+  check_root
+  ./safesetid-test
+}
+
+main_function
+echo "$TCID: done"
+exit $errcode