[PATCH] selftests/socket: Introduce simple SCM_RIGHTS tests

[Kees Cook <keescook@chromium.org>]

This makes sure that simple SCM_RIGHTS fd passing works as expected, to
avoid any future regressions. This is mostly code from Michael Kerrisk's
examples on how to set up and perform fd passing with SCM_RIGHTS. Add
a test script and wire it up to the selftests.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
FYI, this also relicenses Michael's code (with his permission) from
GPL3+ to GPL2+, who is on CC to publicly confirm. :) Thank you Michael!
---
 tools/testing/selftests/Makefile              |   1 +
 tools/testing/selftests/socket/.gitignore     |   4 +
 tools/testing/selftests/socket/Makefile       |  11 ++
 tools/testing/selftests/socket/hello.txt      |   1 +
 tools/testing/selftests/socket/scm_rights.h   |  40 +++++
 .../selftests/socket/scm_rights_recv.c        | 168 ++++++++++++++++++
 .../selftests/socket/scm_rights_send.c        | 144 +++++++++++++++
 .../selftests/socket/simple_scm_rights.sh     |  30 ++++
 tools/testing/selftests/socket/unix_sockets.c |  88 +++++++++
 tools/testing/selftests/socket/unix_sockets.h |  23 +++
 10 files changed, 510 insertions(+)
 create mode 100644 tools/testing/selftests/socket/.gitignore
 create mode 100644 tools/testing/selftests/socket/Makefile
 create mode 100644 tools/testing/selftests/socket/hello.txt
 create mode 100644 tools/testing/selftests/socket/scm_rights.h
 create mode 100644 tools/testing/selftests/socket/scm_rights_recv.c
 create mode 100644 tools/testing/selftests/socket/scm_rights_send.c
 create mode 100755 tools/testing/selftests/socket/simple_scm_rights.sh
 create mode 100644 tools/testing/selftests/socket/unix_sockets.c
 create mode 100644 tools/testing/selftests/socket/unix_sockets.h

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index e03bc15ce731..97e155596660 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -51,6 +51,7 @@ TARGETS += rtc
 TARGETS += seccomp
 TARGETS += sigaltstack
 TARGETS += size
+TARGETS += socket
 TARGETS += sparc64
 TARGETS += splice
 TARGETS += static_keys
diff --git a/tools/testing/selftests/socket/.gitignore b/tools/testing/selftests/socket/.gitignore
new file mode 100644
index 000000000000..bc9a892956b0
--- /dev/null
+++ b/tools/testing/selftests/socket/.gitignore
@@ -0,0 +1,4 @@
+unix_sockets.o
+scm_rights_send
+scm_rights_recv
+scm_rights
diff --git a/tools/testing/selftests/socket/Makefile b/tools/testing/selftests/socket/Makefile
new file mode 100644
index 000000000000..3eb7ef0db997
--- /dev/null
+++ b/tools/testing/selftests/socket/Makefile
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0+
+TEST_PROGS := simple_scm_rights.sh
+TEST_GEN_PROGS_EXTENDED := scm_rights_send scm_rights_recv
+
+include ../lib.mk
+
+$(OUTPUT)/unix_sockets.o: unix_sockets.h
+$(OUTPUT)/scm_rights_recv: $(OUTPUT)/unix_sockets.o scm_rights.h
+$(OUTPUT)/scm_rights_send: $(OUTPUT)/unix_sockets.o scm_rights.h
+
+EXTRA_CLEAN += $(OUTPUT)/unix_sockets.o $(OUTPUT)/scm_rights
diff --git a/tools/testing/selftests/socket/hello.txt b/tools/testing/selftests/socket/hello.txt
new file mode 100644
index 000000000000..e965047ad7c5
--- /dev/null
+++ b/tools/testing/selftests/socket/hello.txt
@@ -0,0 +1 @@
+Hello
diff --git a/tools/testing/selftests/socket/scm_rights.h b/tools/testing/selftests/socket/scm_rights.h
new file mode 100644
index 000000000000..4501a46bf1be
--- /dev/null
+++ b/tools/testing/selftests/socket/scm_rights.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * scm_rights.h
+ *
+ *  Copyright (C) Michael Kerrisk, 2020.
+ *
+ *  Header file used by scm_rights_send.c and scm_rights_recv.c.
+ */
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+#include "unix_sockets.h"
+
+#define SOCK_PATH "scm_rights"
+
+#define errExit(fmt, ...) do {					\
+		fprintf(stderr, fmt, ## __VA_ARGS__);		\
+		fprintf(stderr, ": %s\n", strerror(errno));	\
+		exit(EXIT_FAILURE);				\
+	} while (0)
+
+#define fatal(str) errExit("%s\n", str)
+
+#define usageErr(fmt, ...) do {					\
+		fprintf(stderr, "Usage: ");			\
+		fprintf(stderr, fmt, ## __VA_ARGS__);		\
+		exit(EXIT_FAILURE);				\
+	} while (0)
+
+static bool debugging;
+
+#define debug(fmt, ...) do {					\
+		if (debugging)					\
+			fprintf(stderr, fmt, ## __VA_ARGS__);	\
+	} while (0)
diff --git a/tools/testing/selftests/socket/scm_rights_recv.c b/tools/testing/selftests/socket/scm_rights_recv.c
new file mode 100644
index 000000000000..4c916e43c319
--- /dev/null
+++ b/tools/testing/selftests/socket/scm_rights_recv.c
@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * scm_rights_recv.c
+ *
+ * Copyright (C) Michael Kerrisk, 2020.
+ *
+ * Used in conjunction with scm_rights_send.c to demonstrate passing of
+ * file descriptors via a UNIX domain socket.
+ *
+ * This program receives a file descriptor sent to a UNIX domain socket.
+ *
+ * Usage is as shown in the usageErr() call below.
+ *
+ * File descriptors can be exchanged over stream or datagram sockets. This
+ * program uses stream sockets by default; the "-d" command-line option
+ * specifies that datagram sockets should be used instead.
+ *
+ * This program is Linux-specific.
+ */
+#include "scm_rights.h"
+
+#define BUF_SIZE 100
+
+int
+main(int argc, char *argv[])
+{
+	int data, lfd, sfd, fd, opt;
+	ssize_t nr;
+	bool useDatagramSocket;
+	struct msghdr msgh;
+	struct iovec iov;
+
+	/* Allocate a char array of suitable size to hold the ancillary data.
+	 * However, since this buffer is in reality a 'struct cmsghdr', use a
+	 * union to ensure that it is aligned as required for that structure.
+	 * Alternatively, we could allocate the buffer using malloc(), which
+	 * returns a buffer that satisfies the strictest alignment
+	 * requirements of any type
+	 */
+
+	union {
+		char   buf[CMSG_SPACE(sizeof(int))];
+		/* Space large enough to hold an 'int' */
+		struct cmsghdr align;
+	} controlMsg;
+	struct cmsghdr *cmsgp;	/* Pointer used to iterate through
+				 * headers in ancillary data
+				 */
+
+	/* Parse command-line options */
+
+	useDatagramSocket = false;
+
+	while ((opt = getopt(argc, argv, "dD")) != -1) {
+		switch (opt) {
+		case 'd':
+			useDatagramSocket = true;
+			break;
+
+		default:
+			usageErr("%s [-dD]\n"
+					 "		-D	enable debugging\n"
+					 "		-d	use datagram socket\n", argv[0]);
+		}
+	}
+
+	/* Create socket bound to a well-known address. In the case where
+	 * we are using stream sockets, also make the socket a listening
+	 * socket and accept a connection on the socket.
+	 */
+
+	if (remove(SOCK_PATH) == -1 && errno != ENOENT)
+		errExit("remove-%s", SOCK_PATH);
+
+	if (useDatagramSocket) {
+		sfd = unixBind(SOCK_PATH, SOCK_DGRAM);
+		if (sfd == -1)
+			errExit("unixBind");
+
+	} else {
+		lfd = unixBind(SOCK_PATH, SOCK_STREAM);
+		if (lfd == -1)
+			errExit("unixBind");
+
+		if (listen(lfd, 5) == -1)
+			errExit("listen");
+
+		sfd = accept(lfd, NULL, NULL);
+		if (sfd == -1)
+			errExit("accept");
+	}
+
+	/* The 'msg_name' field can be set to point to a buffer where the
+	 * kernel will place the address of the peer socket. However, we don't
+	 * need the address of the peer, so we set this field to NULL.
+	 */
+
+	msgh.msg_name = NULL;
+	msgh.msg_namelen = 0;
+
+	/* Set fields of 'msgh' to point to buffer used to receive the (real)
+	 * data read by recvmsg()
+	 */
+
+	msgh.msg_iov = &iov;
+	msgh.msg_iovlen = 1;
+	iov.iov_base = &data;
+	iov.iov_len = sizeof(int);
+
+	/* Set 'msgh' fields to describe the ancillary data buffer */
+
+	msgh.msg_control = controlMsg.buf;
+	msgh.msg_controllen = sizeof(controlMsg.buf);
+
+	/* Receive real plus ancillary data */
+
+	nr = recvmsg(sfd, &msgh, 0);
+	if (nr == -1)
+		errExit("recvmsg");
+	debug("recvmsg() returned %ld\n", (long) nr);
+
+	if (nr > 0)
+		debug("Received data = %d\n", data);
+
+	/* Get the address of the first 'cmsghdr' in the received
+	 * ancillary data
+	 */
+
+	cmsgp = CMSG_FIRSTHDR(&msgh);
+
+	/* Check the validity of the 'cmsghdr' */
+
+	if (cmsgp == NULL || cmsgp->cmsg_len != CMSG_LEN(sizeof(int)))
+		fatal("bad cmsg header / message length");
+	if (cmsgp->cmsg_level != SOL_SOCKET)
+		fatal("cmsg_level != SOL_SOCKET");
+	if (cmsgp->cmsg_type != SCM_RIGHTS)
+		fatal("cmsg_type != SCM_RIGHTS");
+
+	/* The data area of the 'cmsghdr' is an 'int' (a file descriptor);
+	 * copy that integer to a local variable. (The received file descriptor
+	 * is typically a different file descriptor number than was used in the
+	 * sending process.)
+	 */
+
+	memcpy(&fd, CMSG_DATA(cmsgp), sizeof(int));
+	debug("Received FD %d\n", fd);
+
+	/* Having obtained the file descriptor, read the file's contents and
+	 * print them on standard output
+	 */
+
+	for (;;) {
+		char buf[BUF_SIZE];
+		ssize_t numRead;
+
+		numRead = read(fd, buf, BUF_SIZE);
+		if (numRead == -1)
+			errExit("read");
+
+		if (numRead == 0)
+			break;
+
+		write(STDOUT_FILENO, buf, numRead);
+	}
+
+	exit(EXIT_SUCCESS);
+}
diff --git a/tools/testing/selftests/socket/scm_rights_send.c b/tools/testing/selftests/socket/scm_rights_send.c
new file mode 100644
index 000000000000..c5718d10a80d
--- /dev/null
+++ b/tools/testing/selftests/socket/scm_rights_send.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * scm_rights_send.c
+ *
+ * Copyright (C) Michael Kerrisk, 2020.
+ *
+ * Used in conjunction with scm_rights_recv.c to demonstrate passing of
+ * file descriptors via a UNIX domain socket.
+ *
+ * This program sends a file descriptor to a UNIX domain socket.
+ *
+ * Usage is as shown in the usageErr() call below.
+ *
+ * File descriptors can be exchanged over stream or datagram sockets. This
+ * program uses stream sockets by default; the "-d" command-line option
+ * specifies that datagram sockets should be used instead.
+ *
+ * This program is Linux-specific.
+ */
+#include "scm_rights.h"
+
+int
+main(int argc, char *argv[])
+{
+	int data, sfd, opt, fd;
+	ssize_t ns;
+	bool useDatagramSocket;
+	struct msghdr msgh;
+	struct iovec iov;
+
+	/* Allocate a char array of suitable size to hold the ancillary data.
+	 * However, since this buffer is in reality a 'struct cmsghdr', use a
+	 * union to ensure that it is aligned as required for that structure.
+	 * Alternatively, we could allocate the buffer using malloc(), which
+	 * returns a buffer that satisfies the strictest alignment
+	 * requirements of any type.
+	 */
+
+	union {
+		char   buf[CMSG_SPACE(sizeof(int))];
+		/* Space large enough to hold an 'int' */
+		struct cmsghdr align;
+	} controlMsg;
+	struct cmsghdr *cmsgp;	/* Pointer used to iterate through
+				 * headers in ancillary data
+				 */
+
+	/* Parse command-line options */
+
+	useDatagramSocket = false;
+
+	while ((opt = getopt(argc, argv, "dD")) != -1) {
+		switch (opt) {
+		case 'd':
+			useDatagramSocket = true;
+			break;
+		case 'D':
+			debugging = true;
+			break;
+		default:
+			usageErr("%s [-dD] file\n"
+					 "		-D	enable debugging\n"
+					 "		-d	use datagram socket\n", argv[0]);
+		}
+	}
+
+	if (argc != optind + 1)
+		usageErr("%s [-dD] file\n", argv[0]);
+
+	/* Open the file named on the command line */
+
+	fd = open(argv[optind], O_RDONLY);
+	if (fd == -1)
+		errExit("open");
+
+	/* The 'msg_name' field can be used to specify the address of the
+	 * destination socket when sending a datagram. However, we do not
+	 * need to use this field because we use connect() below, which sets
+	 * a default outgoing address for datagrams.
+	 */
+
+	msgh.msg_name = NULL;
+	msgh.msg_namelen = 0;
+
+	/* On Linux, we must transmit at least 1 byte of real data in
+	 * order to send ancillary data
+	 */
+
+	msgh.msg_iov = &iov;
+	msgh.msg_iovlen = 1;
+	iov.iov_base = &data;
+	iov.iov_len = sizeof(int);
+	data = 12345;
+	debug("Sending data = %d\n", data);
+
+	/* Set 'msgh' fields to describe the ancillary data buffer */
+
+	msgh.msg_control = controlMsg.buf;
+	msgh.msg_controllen = sizeof(controlMsg.buf);
+
+	/* The control message buffer must be zero-initialized in order
+	 * for the CMSG_NXTHDR() macro to work correctly. Although we
+	 * don't need to use CMSG_NXTHDR() in this example (because
+	 * there is only one block of ancillary data), we show this
+	 * step to demonstrate best practice
+	 */
+
+	memset(controlMsg.buf, 0, sizeof(controlMsg.buf));
+
+	/* Set message header to describe the ancillary data that
+	 * we want to send
+	 */
+
+	cmsgp = CMSG_FIRSTHDR(&msgh);
+	cmsgp->cmsg_len = CMSG_LEN(sizeof(int));
+	cmsgp->cmsg_level = SOL_SOCKET;
+	cmsgp->cmsg_type = SCM_RIGHTS;
+	memcpy(CMSG_DATA(cmsgp), &fd, sizeof(int));
+
+	/* Connect to the peer socket */
+
+	sfd = unixConnect(SOCK_PATH, useDatagramSocket ? SOCK_DGRAM : SOCK_STREAM);
+	if (sfd == -1)
+		errExit("unixConnect");
+
+	debug("Sending FD %d\n", fd);
+
+	/* Send real plus ancillary data */
+
+	ns = sendmsg(sfd, &msgh, 0);
+	if (ns == -1)
+		errExit("sendmsg");
+
+	debug("sendmsg() returned %ld\n", (long) ns);
+
+	/* Once the file descriptor has been sent, it is no longer necessary
+	 * to keep it open in the sending process
+	 */
+
+	if (close(fd) == -1)
+		errExit("close");
+
+	exit(EXIT_SUCCESS);
+}
diff --git a/tools/testing/selftests/socket/simple_scm_rights.sh b/tools/testing/selftests/socket/simple_scm_rights.sh
new file mode 100755
index 000000000000..31ea0fc1bb6d
--- /dev/null
+++ b/tools/testing/selftests/socket/simple_scm_rights.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0+
+set -e
+
+ret=0
+hello=$(cat hello.txt)
+
+rm -f scm_rights
+(sleep 0.1; ./scm_rights_send hello.txt) &
+out=$(./scm_rights_recv)
+
+if [ "$hello" != "$out" ] ; then
+	echo "FAIL: SCM_RIGHTS fd contents mismatch"
+	ret=1
+else
+	echo "ok: SOCK_STREAM"
+fi
+
+rm -f scm_rights
+(sleep 0.1; ./scm_rights_send -d hello.txt) &
+out=$(./scm_rights_recv -d)
+
+if [ "$hello" != "$out" ] ; then
+	echo "FAIL: SCM_RIGHTS fd contents mismatch"
+	ret=1
+else
+	echo "ok: SOCK_DGRAM"
+fi
+
+exit $ret
diff --git a/tools/testing/selftests/socket/unix_sockets.c b/tools/testing/selftests/socket/unix_sockets.c
new file mode 100644
index 000000000000..a7678fad1a16
--- /dev/null
+++ b/tools/testing/selftests/socket/unix_sockets.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * unix_sockets.c
+ *
+ * Copyright (C) Michael Kerrisk, 2020.
+ *
+ * A package of useful routines for UNIX domain sockets.
+ */
+#include "unix_sockets.h"	   /* Declares functions defined here */
+
+/* Build a UNIX domain socket address structure for 'path', returning
+ * it in 'addr'. Returns -1 on success, or 0 on error.
+ */
+
+int
+unixBuildAddress(const char *path, struct sockaddr_un *addr)
+{
+	if (addr == NULL || path == NULL) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	memset(addr, 0, sizeof(struct sockaddr_un));
+	addr->sun_family = AF_UNIX;
+	if (strlen(path) < sizeof(addr->sun_path)) {
+		strncpy(addr->sun_path, path, sizeof(addr->sun_path) - 1);
+		return 0;
+	} else {
+		errno = ENAMETOOLONG;
+		return -1;
+	}
+}
+
+/* Create a UNIX domain socket of type 'type' and connect it
+ * to the remote address specified by the 'path'.
+ * Return the socket descriptor on success, or -1 on error
+ */
+
+int
+unixConnect(const char *path, int type)
+{
+	int sd, savedErrno;
+	struct sockaddr_un addr;
+
+	if (unixBuildAddress(path, &addr) == -1)
+		return -1;
+
+	sd = socket(AF_UNIX, type, 0);
+	if (sd == -1)
+		return -1;
+
+	if (connect(sd, (struct sockaddr *) &addr,
+				sizeof(struct sockaddr_un)) == -1) {
+		savedErrno = errno;
+		close(sd);			  /* Might change 'errno' */
+		errno = savedErrno;
+		return -1;
+	}
+
+	return sd;
+}
+
+/* Create a UNIX domain socket and bind it to 'path'.
+ * Return the socket descriptor on success, or -1 on error.
+ */
+
+int
+unixBind(const char *path, int type)
+{
+	int sd, savedErrno;
+	struct sockaddr_un addr;
+
+	if (unixBuildAddress(path, &addr) == -1)
+		return -1;
+
+	sd = socket(AF_UNIX, type, 0);
+	if (sd == -1)
+		return -1;
+
+	if (bind(sd, (struct sockaddr *) &addr, sizeof(struct sockaddr_un)) == -1) {
+		savedErrno = errno;
+		close(sd);			  /* Might change 'errno' */
+		errno = savedErrno;
+		return -1;
+	}
+
+	return sd;
+}
diff --git a/tools/testing/selftests/socket/unix_sockets.h b/tools/testing/selftests/socket/unix_sockets.h
new file mode 100644
index 000000000000..e03a5aecd10c
--- /dev/null
+++ b/tools/testing/selftests/socket/unix_sockets.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ *  unix_sockets.h
+ *
+ *  Copyright (C) Michael Kerrisk, 2020.
+ *
+ *  Header file for unix_sockets.c.
+ */
+#ifndef UNIX_SOCKETS_H
+#define UNIX_SOCKETS_H      /* Prevent accidental double inclusion */
+
+#include <errno.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+int unixBuildAddress(const char *path, struct sockaddr_un *addr);
+
+int unixConnect(const char *path, int type);
+
+int unixBind(const char *path, int type);
+
+#endif
-- 
2.25.1


-- 
Kees Cook