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

Serge E. Hallyn
2020-07-02T20:53:10Z

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@redhat.com>
> ---
> 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