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

Adrian Reber
2020-07-01T06:50:04Z

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.

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