test/ring-leak: add test app demonstrating leak of io_uring instance

Signed-off-by: Jens Axboe <axboe@kernel.dk>

test/Makefile

@@ -1,10 +1,10 @@
 CFLAGS ?= -g -O2 -Wall -D_GNU_SOURCE -L../src/
 
-all_targets += io_uring-test io_uring-cp poll poll-cancel
+all_targets += io_uring-test io_uring-cp poll poll-cancel ring-leak
 
 all: $(all_targets)
 
-test_srcs := io_uring-test.c io_uring-cp.c poll.c poll-cancel.c
+test_srcs := io_uring-test.c io_uring-cp.c poll.c poll-cancel.c ring-leak.c
 
 test_objs := $(patsubst %.c,%.ol,$(test_srcs))
 
@@ -16,5 +16,7 @@ poll: poll.c
 	$(CC) $(CFLAGS) -o $@ poll.c -luring
 poll-cancel: poll-cancel.c
 	$(CC) $(CFLAGS) -o $@ poll-cancel.c -luring
+ring-leak: ring-leak.c
+	$(CC) $(CFLAGS) -o $@ ring-leak.c -luring
 clean:
 	rm -f $(all_targets) $(test_objs)

test/ring-leak.c

@@ -0,0 +1,108 @@
+/*
+ * Based on description from Al Viro - this demonstrates a leak of the
+ * io_uring instance, by sending the io_uring fd over a UNIX socket.
+ *
+ * See:
+ *
+ * https://lore.kernel.org/linux-block/20190129192702.3605-1-axboe@kernel.dk/T/#m6c87fc64e4d063786af6ec6fadce3ac1e95d3184
+ *
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <signal.h>
+#include <inttypes.h>
+#include <sys/types.h>
+#include <sys/syscall.h>
+#include <sys/socket.h>
+#include <sys/wait.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <linux/fs.h>
+
+#include "../src/liburing.h"
+
+static int io_uring_register_files(int ring_fd, int fd1, int fd2)
+{
+	__s32 *fds;
+
+	fds = calloc(2, sizeof(__s32));
+	fds[0] = fd1;
+	fds[1] = fd2;
+
+	return io_uring_register(ring_fd, IORING_REGISTER_FILES, fds, 2);
+}
+
+static int get_ring_fd(void)
+{
+	struct io_uring_params p;
+	int fd;
+
+	memset(&p, 0, sizeof(p));
+
+	fd = io_uring_setup(2, &p);
+	if (fd < 0) {
+		perror("io_uring_setup");
+		return -1;
+	}
+
+	return fd;
+}
+
+static void send_fd(int socket, int fd)
+{
+	char buf[CMSG_SPACE(sizeof(fd))];
+	struct cmsghdr *cmsg;
+	struct msghdr msg;
+
+	memset(buf, 0, sizeof(buf));
+	memset(&msg, 0, sizeof(msg));
+
+	msg.msg_control = buf;
+	msg.msg_controllen = sizeof(buf);
+
+	cmsg = CMSG_FIRSTHDR(&msg);
+	cmsg->cmsg_level = SOL_SOCKET;
+	cmsg->cmsg_type = SCM_RIGHTS;
+	cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
+
+	memmove(CMSG_DATA(cmsg), &fd, sizeof(fd));
+
+	msg.msg_controllen = CMSG_SPACE(sizeof(fd));
+
+	if (sendmsg(socket, &msg, 0) < 0)
+		perror("sendmsg");
+}
+
+int main(int argc, char *argv[])
+{
+	int sp[2], pid, ring_fd, ret;
+
+	if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sp) != 0) {
+		perror("Failed to create Unix-domain socket pair\n");
+		return 1;
+	}
+
+	ring_fd = get_ring_fd();
+	if (ring_fd < 0)
+		return 1;
+
+	ret = io_uring_register_files(ring_fd, sp[0], sp[1]);
+	if (ret < 0) {
+		perror("register files");
+		return 1;
+	}
+
+	pid = fork();
+	if (pid) {
+		printf("Sending fd %d\n", ring_fd);
+
+		send_fd(sp[0], ring_fd);
+	}
+
+	close(ring_fd);
+	close(sp[0]);
+	close(sp[1]);
+	return 0;
+}