zdtm: Check many processes with common dead pidfd

We have multiple processes open a pidfd to a common dead process.
After C/R we check that the inode numbers for these pidfds are equal or
not.

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

test/zdtm/static/Makefile

@@ -56,6 +56,7 @@ TST_NOFILE	:=				\
 		pidfd_self			\
 		pidfd_of_thread			\
 		pidfd_dead			\
+		pidfd_diffdead			\
 		pidfd_child			\
 		pidfd_kill			\
 		fd_from_pidfd			\

test/zdtm/static/pidfd_diffdead.c

@@ -0,0 +1,228 @@
+#include <sys/statfs.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc = "Check C/R of processes that point to a common dead pidfd\n";
+const char *test_author = "Bhavik Sachdev <b.sachdev1904@gmail.com>";
+
+#ifndef PID_FS_MAGIC
+#define PID_FS_MAGIC 0x50494446
+#endif
+
+/*
+ * main
+ *	`- child
+ *		`- grandchild
+ *
+ * main and child open a pidfd for grandchild.
+ * Before C/R we kill grandchild.
+ * We end up with two pidfds in two diff processes that point to the same dead process.
+ */
+
+static long get_fs_type(int lfd)
+{
+	struct statfs fst;
+
+	if (fstatfs(lfd, &fst)) {
+		return -1;
+	}
+	return fst.f_type;
+}
+
+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 check_for_pidfs(void)
+{
+	long type;
+	int pidfd = pidfd_open(getpid(), 0);
+	if (pidfd < 0) {
+		pr_perror("pidfd open() failed");
+		return -1;
+	}
+	type = get_fs_type(pidfd);
+	close(pidfd);
+	return type == PID_FS_MAGIC;
+}
+
+int main(int argc, char *argv[])
+{
+#define READ  0
+#define WRITE 1
+
+	int child, ret, gchild, status;
+	struct statx stat;
+	task_waiter_t t;
+	unsigned long long ino;
+
+	/*
+	 * We use the inop pipe to send the inode number of the
+	 * pidfd opened in the child to the main process for
+	 * comparison.
+	 */
+	int p[2];
+	int pidfd;
+
+	test_init(argc, argv);
+	task_waiter_init(&t);
+
+	ret = check_for_pidfs();
+	if (ret < 0)
+		return 1;
+
+	if (ret == 0) {
+		test_daemon();
+		test_waitsig();
+		skip("Test requires pidfs. skipping...");
+		pass();
+		return 0;
+	}
+
+	if (pipe(p)) {
+		pr_perror("pipe");
+		return 1;
+	}
+
+	child = test_fork();
+	if (child < 0) {
+		pr_perror("fork");
+		return 1;
+	} else if (child == 0) {
+		int gchild;
+		gchild = test_fork();
+		if (gchild < 0) {
+			pr_perror("fork");
+			return 1;
+		} else if (gchild == 0) {
+			close(p[READ]);
+			close(p[WRITE]);
+			while (1)
+				sleep(1000);
+		} else {
+			if (write(p[WRITE], &gchild, sizeof(int)) != sizeof(int)) {
+				pr_perror("write");
+				return 1;
+			}
+
+			pidfd = pidfd_open(gchild, 0);
+			if (pidfd < 0) {
+				pr_perror("pidfd_open");
+				return 1;
+			}
+
+			if (waitpid(gchild, &status, 0) != gchild) {
+				pr_perror("waitpid");
+				return 1;
+			}
+
+			if (!WIFSIGNALED(status)) {
+				fail("Expected grandchild to be terminated by a signal");
+				return 1;
+			}
+
+			if (WTERMSIG(status) != SIGKILL) {
+				fail("Expected grandchild to be terminated by SIGKILL");
+				return 1;
+			}
+			task_waiter_complete(&t, 1);
+
+			test_waitsig();
+
+			if (statx(pidfd, "", AT_EMPTY_PATH, STATX_ALL, &stat) < 0) {
+				pr_perror("statx");
+				return 1;
+			}
+
+			close(p[WRITE]);
+			if (read(p[READ], &ino, sizeof(ino)) != sizeof(ino)) {
+				pr_perror("read");
+				return 1;
+			}
+			close(p[READ]);
+			close(pidfd);
+
+			/* ino number should be same because both pidfds were for the same process */
+			if (ino != stat.stx_ino) {
+				exit(1);
+			}
+			exit(0);
+		}
+	}
+
+	if (read(p[READ], &gchild, sizeof(int)) != sizeof(int)) {
+		pr_perror("write");
+		return 1;
+	}
+
+	pidfd = pidfd_open(gchild, 0);
+	if (pidfd < 0) {
+		pr_perror("pidfd_open");
+		return 1;
+	}
+
+	/*
+	* We kill grandchild process only after opening pidfd.
+	*/
+	if (pidfd_send_signal(pidfd, SIGKILL, NULL, 0)) {
+		pr_perror("pidfd_send_signal");
+		return 1;
+	}
+
+	/* Wait for child to waitpid on gchild */
+	task_waiter_wait4(&t, 1);
+
+	test_daemon();
+	test_waitsig();
+
+	close(p[READ]);
+	if (statx(pidfd, "", AT_EMPTY_PATH, STATX_ALL, &stat) < 0) {
+		pr_perror("statx");
+		goto err;
+	}
+
+	/* Send inode number of pidfd to child for comparison */
+	if (write(p[WRITE], &stat.stx_ino, sizeof(stat.stx_ino)) != sizeof(stat.stx_ino)) {
+		pr_perror("write");
+		goto err;
+	}
+	close(p[WRITE]);
+
+	if (kill(child, SIGTERM)) {
+		pr_perror("kill");
+		goto err;
+	}
+
+	if (waitpid(child, &status, 0) != child) {
+		pr_perror("waitpid");
+		goto err;
+	}
+
+	if (!WIFEXITED(status)) {
+		fail("Expected child to terminate normally");
+		goto err;
+	}
+
+	if (WEXITSTATUS(status) != 0) {
+		fail("Child failed");
+		goto err;
+	}
+
+	pass();
+	close(pidfd);
+	return 0;
+err:
+	close(pidfd);
+	return 1;
+}