zdtm: Check pidfd can kill descendant processes

Validate that pidfds can been used to send signals to different
processes after C/R using the `pidfd_send_signal()` syscall.

Signed-off-by: Bhavik Sachdev <b.sachdev1904@gmail.com>

test/zdtm/static/Makefile

@@ -55,6 +55,7 @@ TST_NOFILE	:=				\
 		ptrace_sig			\
 		pidfd_self			\
 		pidfd_child			\
+		pidfd_kill			\
 		pipe00				\
 		pipe01				\
 		pipe02				\

test/zdtm/static/pidfd_kill.c

@@ -0,0 +1,128 @@
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc = "Kill child and grandchild process using pidfds\n";
+const char *test_author = "Bhavik Sachdev <b.sachdev1904@gmail.com>";
+
+static int pidfd_open(pid_t pid, unsigned int flags)
+{
+	return syscall(__NR_pidfd_open, pid, flags);
+}
+
+static int pidfd_send_signal(int pidfd, int sig, siginfo_t* info, unsigned int flags)
+{
+	return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
+}
+
+static int wait_for_child(int child)
+{
+	int status;
+	if (waitpid(child, &status, 0) != child) {
+		pr_perror("waitpid()");
+		return 1;
+	}
+
+	if (status != 0) {
+		test_msg("%d:%d:%d:%d", WIFEXITED(status), WEXITSTATUS(status),
+			WIFSIGNALED(status), WTERMSIG(status));
+	}
+
+	return 0;
+}
+
+int main(int argc, char* argv[])
+{
+	#define READ 0
+	#define WRITE 1
+
+	int child, gchild, cpidfd, gpidfd, gchild_pid, ret;
+	int p[2];
+
+	if (pipe(p)) {
+		pr_perror("pipe");
+		return 1;
+	}
+
+	test_init(argc, argv);
+
+	child = fork();
+	if (child < 0) {
+		pr_perror("fork");
+		return 1;
+	}
+
+	if (child == 0) {
+		gchild = fork();
+		if (gchild < 0) {
+			pr_perror("fork");
+			return 1;
+		}
+
+		if (gchild == 0) {
+			test_waitsig();
+			return 0;
+		}
+
+		close(p[READ]);
+		if (write(p[WRITE], &gchild, sizeof(gchild))
+			!= sizeof(gchild)) {
+			pr_perror("write");
+			return 1;
+		}
+		close(p[WRITE]);
+
+		test_waitsig();
+		return wait_for_child(gchild);
+	}
+
+	cpidfd = pidfd_open(child, 0);
+	if (cpidfd < 0) {
+		pr_perror("pidfd_open");
+		return 1;
+	}
+
+	close(p[WRITE]);
+	if (read(p[READ], &gchild_pid, sizeof(gchild_pid))
+		!= sizeof(gchild_pid)) {
+		pr_perror("read");
+		return 1;
+	}
+	close(p[READ]);
+
+	gpidfd = pidfd_open(gchild_pid, 0);
+	if (gpidfd < 0) {
+		pr_perror("pidfd_open");
+		return 1;
+	}
+
+	test_daemon();
+	test_waitsig();
+
+	if (pidfd_send_signal(gpidfd, SIGKILL, NULL, 0)) {
+		pr_perror("Could not send signal");
+		goto fail_close;
+	}
+
+	if (pidfd_send_signal(cpidfd, SIGKILL, NULL, 0)) {
+		pr_perror("Could not send signal");
+		goto fail_close;
+	}
+
+	ret = wait_for_child(child);
+	if (ret)
+		goto fail_close;
+
+	pass();
+	close(cpidfd);
+	close(gpidfd);
+	return 0;
+
+fail_close:
+	fail();
+	close(cpidfd);
+	close(gpidfd);
+	return 1;
+}