ipv6_fragmentation.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Author: Brett A C Sheffield <bacs@librecast.net>
  4 *
  5 * Kernel selftest for the IPv6 fragmentation regression which affected stable
  6 * kernels:
  7 *
  8 *   https://lore.kernel.org/stable/aElivdUXqd1OqgMY@karahi.gladserv.com
  9 *
 10 * Commit: a18dfa9925b9 ("ipv6: save dontfrag in cork") was backported to stable
 11 * without some prerequisite commits.
 12 *
 13 * This caused a regression when sending IPv6 UDP packets by preventing
 14 * fragmentation and instead returning -1 (EMSGSIZE).
 15 *
 16 * This selftest demonstrates the issue by sending an IPv6 UDP packet to
 17 * localhost (::1) on the loopback interface from the autoconfigured link-local
 18 * address.
 19 *
 20 * sendmsg(2) returns bytes sent correctly on a working kernel, and returns -1
 21 * (EMSGSIZE) when the regression is present.
 22 *
 23 * The regression was not present in the mainline kernel, but add this test to
 24 * catch similar breakage in future.
 25 */
 26
 27#define _GNU_SOURCE
 28
 29#include <error.h>
 30#include <net/if.h>
 31#include <netinet/in.h>
 32#include <sched.h>
 33#include <stdio.h>
 34#include <sys/ioctl.h>
 35#include <sys/socket.h>
 36#include <unistd.h>
 37#include "kselftest.h"
 38
 39#define MTU 1500
 40#define LARGER_THAN_MTU 8192
 41
 42static void setup(void)
 43{
 44	struct ifreq ifr = {
 45		.ifr_name = "lo"
 46	};
 47	int ctl;
 48
 49	/* we need to set MTU, so do this in a namespace to play nicely */
 50	if (unshare(CLONE_NEWNET) == -1)
 51		error(KSFT_FAIL, errno, "unshare");
 52
 53	ctl = socket(AF_LOCAL, SOCK_STREAM, 0);
 54	if (ctl == -1)
 55		error(KSFT_FAIL, errno, "socket");
 56
 57	/* ensure MTU is smaller than what we plan to send */
 58	ifr.ifr_mtu = MTU;
 59	if (ioctl(ctl, SIOCSIFMTU, &ifr) == -1)
 60		error(KSFT_FAIL, errno, "ioctl: set MTU");
 61
 62	/* bring up interface */
 63	if (ioctl(ctl, SIOCGIFFLAGS, &ifr) == -1)
 64		error(KSFT_FAIL, errno, "ioctl SIOCGIFFLAGS");
 65	ifr.ifr_flags = ifr.ifr_flags | IFF_UP;
 66	if (ioctl(ctl, SIOCSIFFLAGS, &ifr) == -1)
 67		error(KSFT_FAIL, errno, "ioctl: bring interface up");
 68
 69	if (close(ctl) == -1)
 70		error(KSFT_FAIL, errno, "close");
 71}
 72
 73int main(void)
 74{
 75	struct in6_addr addr = {
 76		.s6_addr[15] = 0x01,  /* ::1 */
 77	};
 78	struct sockaddr_in6 sa = {
 79		.sin6_family = AF_INET6,
 80		.sin6_addr = addr,
 81		.sin6_port = htons(9) /* port 9/udp (DISCARD) */
 82	};
 83	static char buf[LARGER_THAN_MTU] = {0};
 84	struct iovec iov = { .iov_base = buf, .iov_len = sizeof(buf) };
 85	struct msghdr msg = {
 86		.msg_iov = &iov,
 87		.msg_iovlen = 1,
 88		.msg_name = (struct sockaddr *)&sa,
 89		.msg_namelen = sizeof(sa),
 90	};
 91	ssize_t rc;
 92	int s;
 93
 94	printf("Testing IPv6 fragmentation\n");
 95	setup();
 96	s = socket(AF_INET6, SOCK_DGRAM, 0);
 97send_again:
 98	rc = sendmsg(s, &msg, 0);
 99	if (rc == -1) {
100		/* if interface wasn't ready, try again */
101		if (errno == EADDRNOTAVAIL) {
102			usleep(1000);
103			goto send_again;
104		}
105		error(KSFT_FAIL, errno, "sendmsg");
106	} else if (rc != LARGER_THAN_MTU) {
107		error(KSFT_FAIL, errno, "sendmsg returned %zi, expected %i",
108				rc, LARGER_THAN_MTU);
109	}
110	printf("[PASS] sendmsg() returned %zi\n", rc);
111	if (close(s) == -1)
112		error(KSFT_FAIL, errno, "close");
113	return KSFT_PASS;
114}