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

[Serge E. Hallyn]

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.


> 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