selftest: bpf: Add test for bpf_unix_scrub_fds().

This test performs the following for all AF_UNIX socket types

  1. Create a socket pair (sender and receiver)
  2. Send the receiver's fd from the sender to the receiver
  3. Receive the fd
  4. Attach a BPF LSM prog that scrubs SCM_RIGHTS fds
  5. Send the receiver's fd from the sender to the receiver
  6. Check if the fd was scrubbed
  7. Detach the LSM prog

How to run:

  # make -C tools/testing/selftests/bpf/
  # ./tools/testing/selftests/bpf/test_progs -t lsm_unix_may_send
  ...
  torvalds#175/1   lsm_unix_may_send/SOCK_STREAM:OK
  torvalds#175/2   lsm_unix_may_send/SOCK_DGRAM:OK
  torvalds#175/3   lsm_unix_may_send/SOCK_SEQPACKET:OK
  torvalds#175     lsm_unix_may_send:OK
  Summary: 1/3 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Kuniyuki Iwashima <[email protected]>

Author: q2ven

tools/testing/selftests/bpf/prog_tests/lsm_unix_may_send.c

@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright Amazon.com Inc. or its affiliates. */
+
+#include "test_progs.h"
+#include "lsm_unix_may_send.skel.h"
+
+#define MSG_HELLO "Hello"
+#define MSG_WORLD "World"
+#define MSG_LEN 5
+
+struct scm_rights {
+	struct cmsghdr cmsghdr;
+	int fd;
+};
+
+static int send_fd(int sender_fd, int receiver_fd)
+{
+	struct scm_rights cmsg = {};
+	struct msghdr msg = {};
+	struct iovec iov = {};
+	int ret;
+
+	msg.msg_iov = &iov;
+	msg.msg_iovlen = 1;
+	msg.msg_control = &cmsg;
+	msg.msg_controllen = CMSG_SPACE(sizeof(cmsg.fd));
+
+	iov.iov_base = MSG_HELLO;
+	iov.iov_len = MSG_LEN;
+
+	cmsg.cmsghdr.cmsg_len = CMSG_LEN(sizeof(cmsg.fd));
+	cmsg.cmsghdr.cmsg_level = SOL_SOCKET;
+	cmsg.cmsghdr.cmsg_type = SCM_RIGHTS;
+	cmsg.fd = receiver_fd;
+
+	ret = sendmsg(sender_fd, &msg, 0);
+	if (!ASSERT_EQ(ret, MSG_LEN, "sendmsg(Hello)"))
+		return -EINVAL;
+
+	ret = send(sender_fd, MSG_WORLD, MSG_LEN, 0);
+	if (!ASSERT_EQ(ret, MSG_LEN, "sendmsg(World)"))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int recv_fd(int receiver_fd, bool lsm_attached)
+{
+	struct scm_rights cmsg = {};
+	struct msghdr msg = {};
+	char buf[MSG_LEN] = {};
+	struct iovec iov = {};
+	int ret;
+
+	msg.msg_iov = &iov;
+	msg.msg_iovlen = 1;
+	msg.msg_control = &cmsg;
+	msg.msg_controllen = CMSG_SPACE(sizeof(cmsg.fd));
+
+	iov.iov_base = buf;
+	iov.iov_len = sizeof(buf);
+
+	ret = recvmsg(receiver_fd, &msg, 0);
+	if (!ASSERT_EQ(ret, MSG_LEN, "recvmsg(Hello) length") ||
+	    !ASSERT_STRNEQ(buf, MSG_HELLO, MSG_LEN, "recvmsg(Hello) data"))
+		return -EINVAL;
+
+	if (lsm_attached) {
+		if (!ASSERT_ERR_PTR(CMSG_FIRSTHDR(&msg), "cmsg filtered"))
+			return -EINVAL;
+	} else {
+		if (!ASSERT_OK_PTR(CMSG_FIRSTHDR(&msg), "cmsg sent") ||
+		    !ASSERT_EQ(cmsg.cmsghdr.cmsg_len, CMSG_LEN(sizeof(cmsg.fd)), "cmsg_len") ||
+		    !ASSERT_EQ(cmsg.cmsghdr.cmsg_level, SOL_SOCKET, "cmsg_level") ||
+		    !ASSERT_EQ(cmsg.cmsghdr.cmsg_type, SCM_RIGHTS, "cmsg_type"))
+			return -EINVAL;
+
+		receiver_fd = cmsg.fd;
+	}
+
+	memset(buf, 0, sizeof(buf));
+
+	ret = recv(receiver_fd, buf, sizeof(buf), 0);
+	if (!ASSERT_EQ(ret, MSG_LEN, "recvmsg(World) length") ||
+	    !ASSERT_STRNEQ(buf, MSG_WORLD, MSG_LEN, "recvmsg(World) data"))
+		return -EINVAL;
+
+	return 0;
+}
+
+static void test_scm_rights(struct lsm_unix_may_send *skel, int type)
+{
+	struct bpf_link *link;
+	int socket_fds[2];
+	int err;
+
+	err = socketpair(AF_UNIX, type, 0, socket_fds);
+	if (!ASSERT_EQ(err, 0, "socketpair"))
+		return;
+
+	err = send_fd(socket_fds[0], socket_fds[1]);
+	if (err)
+		goto close;
+
+	err = recv_fd(socket_fds[1], false);
+	if (err)
+		goto close;
+
+	link = bpf_program__attach_lsm(skel->progs.unix_scrub_scm_rights);
+	if (!ASSERT_OK_PTR(link, "attach lsm"))
+		goto close;
+
+	err = send_fd(socket_fds[0], socket_fds[1]);
+	if (err)
+		goto close;
+
+	err = recv_fd(socket_fds[1], true);
+	if (err)
+		goto close;
+
+	err = bpf_link__destroy(link);
+	ASSERT_EQ(err, 0, "destroy lsm");
+close:
+	close(socket_fds[0]);
+	close(socket_fds[1]);
+}
+
+struct sk_type {
+	char name[16];
+	int type;
+} sk_types[] = {
+	{
+		.name = "SOCK_STREAM",
+		.type = SOCK_STREAM,
+	},
+	{
+		.name = "SOCK_DGRAM",
+		.type = SOCK_DGRAM,
+	},
+	{
+		.name = "SOCK_SEQPACKET",
+		.type = SOCK_SEQPACKET,
+	},
+};
+
+void test_lsm_unix_may_send(void)
+{
+	struct lsm_unix_may_send *skel;
+	int i;
+
+	skel = lsm_unix_may_send__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "load skel"))
+		return;
+
+	for (i = 0; i < ARRAY_SIZE(sk_types); i++)
+		if (test__start_subtest(sk_types[i].name))
+			test_scm_rights(skel, sk_types[i].type);
+
+	lsm_unix_may_send__destroy(skel);
+}

tools/testing/selftests/bpf/progs/lsm_unix_may_send.c

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright Amazon.com Inc. or its affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_tracing.h>
+
+#ifndef EPERM
+#define EPERM 1
+#endif
+
+SEC("lsm/unix_may_send")
+int BPF_PROG(unix_scrub_scm_rights,
+	     struct socket *sock, struct socket *other, struct sk_buff *skb)
+{
+	struct unix_skb_parms *cb;
+
+	if (!skb)
+		return 0;
+
+	cb = (struct unix_skb_parms *)skb->cb;
+	if (!cb->fp)
+		return 0;
+
+	if (bpf_unix_scrub_fds(skb))
+		return -EPERM;
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";