Re: [PATCH v4 2/3] selftests: add clone3() CAP_CHECKPOINT_RESTORE test

[Adrian Reber]

On Thu, Jul 02, 2020 at 03:53:05PM -0500, Serge E. Hallyn wrote:
> On Wed, Jul 01, 2020 at 08:49:05AM +0200, Adrian Reber wrote:
> > This adds a test that changes its UID, uses capabilities to
> > get CAP_CHECKPOINT_RESTORE and uses clone3() with set_tid to
> > create a process with a given PID as non-root.
> 
> Seems worth also verifying that it fails if you have no capabilities.
> I don't see that in the existing clone3/ test dir.

Bit confused about what you mean. This test does:

 * switch UID to 1000
 * run clone3() with set_tid set and expect EPERM
 * set CAP_CHECKPOINT_RESTORE capability
 * run clone3() with set_tid set and expect success

So it already does what I think you are asking for. Did I misunderstand
your comment?

		Adrian

> > Signed-off-by: Adrian Reber <areber@xxxxxxxxxx>
> > ---
> >  tools/testing/selftests/clone3/Makefile       |   4 +-
> >  .../clone3/clone3_cap_checkpoint_restore.c    | 203 ++++++++++++++++++
> >  2 files changed, 206 insertions(+), 1 deletion(-)
> >  create mode 100644 tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
> > 
> > diff --git a/tools/testing/selftests/clone3/Makefile b/tools/testing/selftests/clone3/Makefile
> > index cf976c732906..ef7564cb7abe 100644
> > --- a/tools/testing/selftests/clone3/Makefile
> > +++ b/tools/testing/selftests/clone3/Makefile
> > @@ -1,6 +1,8 @@
> >  # SPDX-License-Identifier: GPL-2.0
> >  CFLAGS += -g -I../../../../usr/include/
> > +LDLIBS += -lcap
> >  
> > -TEST_GEN_PROGS := clone3 clone3_clear_sighand clone3_set_tid
> > +TEST_GEN_PROGS := clone3 clone3_clear_sighand clone3_set_tid \
> > +	clone3_cap_checkpoint_restore
> >  
> >  include ../lib.mk
> > diff --git a/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
> > new file mode 100644
> > index 000000000000..2cc3d57b91f2
> > --- /dev/null
> > +++ b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
> > @@ -0,0 +1,203 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/*
> > + * Based on Christian Brauner's clone3() example.
> > + * These tests are assuming to be running in the host's
> > + * PID namespace.
> > + */
> > +
> > +/* capabilities related code based on selftests/bpf/test_verifier.c */
> > +
> > +#define _GNU_SOURCE
> > +#include <errno.h>
> > +#include <linux/types.h>
> > +#include <linux/sched.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <stdbool.h>
> > +#include <sys/capability.h>
> > +#include <sys/prctl.h>
> > +#include <sys/syscall.h>
> > +#include <sys/types.h>
> > +#include <sys/un.h>
> > +#include <sys/wait.h>
> > +#include <unistd.h>
> > +#include <sched.h>
> > +
> > +#include "../kselftest.h"
> > +#include "clone3_selftests.h"
> > +
> > +#ifndef MAX_PID_NS_LEVEL
> > +#define MAX_PID_NS_LEVEL 32
> > +#endif
> > +
> > +static void child_exit(int ret)
> > +{
> > +	fflush(stdout);
> > +	fflush(stderr);
> > +	_exit(ret);
> > +}
> > +
> > +static int call_clone3_set_tid(pid_t * set_tid, size_t set_tid_size)
> > +{
> > +	int status;
> > +	pid_t pid = -1;
> > +
> > +	struct clone_args args = {
> > +		.exit_signal = SIGCHLD,
> > +		.set_tid = ptr_to_u64(set_tid),
> > +		.set_tid_size = set_tid_size,
> > +	};
> > +
> > +	pid = sys_clone3(&args, sizeof(struct clone_args));
> > +	if (pid < 0) {
> > +		ksft_print_msg("%s - Failed to create new process\n",
> > +			       strerror(errno));
> > +		return -errno;
> > +	}
> > +
> > +	if (pid == 0) {
> > +		int ret;
> > +		char tmp = 0;
> > +
> > +		ksft_print_msg
> > +		    ("I am the child, my PID is %d (expected %d)\n",
> > +		     getpid(), set_tid[0]);
> > +
> > +		if (set_tid[0] != getpid())
> > +			child_exit(EXIT_FAILURE);
> > +		child_exit(EXIT_SUCCESS);
> > +	}
> > +
> > +	ksft_print_msg("I am the parent (%d). My child's pid is %d\n",
> > +		       getpid(), pid);
> > +
> > +	if (waitpid(pid, &status, 0) < 0) {
> > +		ksft_print_msg("Child returned %s\n", strerror(errno));
> > +		return -errno;
> > +	}
> > +
> > +	if (!WIFEXITED(status))
> > +		return -1;
> > +
> > +	return WEXITSTATUS(status);
> > +}
> > +
> > +static int test_clone3_set_tid(pid_t * set_tid,
> > +			       size_t set_tid_size, int expected)
> > +{
> > +	int ret;
> > +
> > +	ksft_print_msg("[%d] Trying clone3() with CLONE_SET_TID to %d\n",
> > +		       getpid(), set_tid[0]);
> > +	ret = call_clone3_set_tid(set_tid, set_tid_size);
> > +
> > +	ksft_print_msg
> > +	    ("[%d] clone3() with CLONE_SET_TID %d says :%d - expected %d\n",
> > +	     getpid(), set_tid[0], ret, expected);
> > +	if (ret != expected) {
> > +		ksft_test_result_fail
> > +		    ("[%d] Result (%d) is different than expected (%d)\n",
> > +		     getpid(), ret, expected);
> > +		return -1;
> > +	}
> > +	ksft_test_result_pass
> > +	    ("[%d] Result (%d) matches expectation (%d)\n", getpid(), ret,
> > +	     expected);
> > +
> > +	return 0;
> > +}
> > +
> > +struct libcap {
> > +	struct __user_cap_header_struct hdr;
> > +	struct __user_cap_data_struct data[2];
> > +};
> > +
> > +static int set_capability()
> > +{
> > +	cap_value_t cap_values[] = { CAP_SETUID, CAP_SETGID };
> > +	struct libcap *cap;
> > +	int ret = -1;
> > +	cap_t caps;
> > +
> > +	caps = cap_get_proc();
> > +	if (!caps) {
> > +		perror("cap_get_proc");
> > +		return -1;
> > +	}
> > +
> > +	/* Drop all capabilities */
> > +	if (cap_clear(caps)) {
> > +		perror("cap_clear");
> > +		goto out;
> > +	}
> > +
> > +	cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_values, CAP_SET);
> > +	cap_set_flag(caps, CAP_PERMITTED, 2, cap_values, CAP_SET);
> > +
> > +	cap = (struct libcap *) caps;
> > +
> > +	/* 40 -> CAP_CHECKPOINT_RESTORE */
> > +	cap->data[1].effective |= 1 << (40 - 32);
> > +	cap->data[1].permitted |= 1 << (40 - 32);
> > +
> > +	if (cap_set_proc(caps)) {
> > +		perror("cap_set_proc");
> > +		goto out;
> > +	}
> > +	ret = 0;
> > +out:
> > +	if (cap_free(caps))
> > +		perror("cap_free");
> > +	return ret;
> > +}
> > +
> > +int main(int argc, char *argv[])
> > +{
> > +	pid_t pid;
> > +	int status;
> > +	int ret = 0;
> > +	pid_t set_tid[1];
> > +	uid_t uid = getuid();
> > +
> > +	ksft_print_header();
> > +	test_clone3_supported();
> > +	ksft_set_plan(2);
> > +
> > +	if (uid != 0) {
> > +		ksft_cnt.ksft_xskip = ksft_plan;
> > +		ksft_print_msg("Skipping all tests as non-root\n");
> > +		return ksft_exit_pass();
> > +	}
> > +
> > +	memset(&set_tid, 0, sizeof(set_tid));
> > +
> > +	/* Find the current active PID */
> > +	pid = fork();
> > +	if (pid == 0) {
> > +		ksft_print_msg("Child has PID %d\n", getpid());
> > +		child_exit(EXIT_SUCCESS);
> > +	}
> > +	if (waitpid(pid, &status, 0) < 0)
> > +		ksft_exit_fail_msg("Waiting for child %d failed", pid);
> > +
> > +	/* After the child has finished, its PID should be free. */
> > +	set_tid[0] = pid;
> > +
> > +	if (set_capability())
> > +		ksft_test_result_fail
> > +		    ("Could not set CAP_CHECKPOINT_RESTORE\n");
> > +	prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0);
> > +	/* This would fail without CAP_CHECKPOINT_RESTORE */
> > +	setgid(1000);
> > +	setuid(1000);
> > +	set_tid[0] = pid;
> > +	ret |= test_clone3_set_tid(set_tid, 1, -EPERM);
> > +	if (set_capability())
> > +		ksft_test_result_fail
> > +		    ("Could not set CAP_CHECKPOINT_RESTORE\n");
> > +	/* This should work as we have CAP_CHECKPOINT_RESTORE as non-root */
> > +	ret |= test_clone3_set_tid(set_tid, 1, 0);
> > +
> > +	return !ret ? ksft_exit_pass() : ksft_exit_fail();
> > +}
> > -- 
> > 2.26.2
>