Commit aeb8d48e authored by Brett A C Sheffield's avatar Brett A C Sheffield Committed by Paolo Abeni
Browse files

selftests: net: add test for ipv6 fragmentation 

Add selftest for the IPv6 fragmentation regression which affected
several stable kernels.

Commit a18dfa99 ("ipv6: save dontfrag in cork") was backported to
stable without some prerequisite commits.  This caused a regression when
sending IPv6 UDP packets by preventing fragmentation and instead
returning -1 (EMSGSIZE).

Add selftest to check for this issue by attempting to send a packet
larger than the interface MTU. The packet will be fragmented on a
working kernel, with sendmsg(2) correctly returning the expected number
of bytes sent.  When the regression is present, sendmsg returns -1 and
sets errno to EMSGSIZE.

Link: https://lore.kernel.org/stable/aElivdUXqd1OqgMY@karahi.gladserv.com


Signed-off-by: default avatarBrett A C Sheffield <bacs@librecast.net>
Reviewed-by: default avatarWillem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250903154925.13481-1-bacs@librecast.net


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent d67ca09c

tools/testing/selftests/net/.gitignore

+1 −0
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ ip_local_port_range 
ipsec

ipv6_flowlabel

ipv6_flowlabel_mgr

ipv6_fragmentation

log.txt

msg_oob

msg_zerocopy

tools/testing/selftests/net/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -118,6 +118,7 @@ TEST_GEN_FILES += tfo 
TEST_PROGS += tfo_passive.sh

TEST_PROGS += broadcast_pmtu.sh

TEST_PROGS += ipv6_force_forwarding.sh

TEST_GEN_PROGS += ipv6_fragmentation

TEST_PROGS += route_hint.sh



# YNL files, must be before "include ..lib.mk"

tools/testing/selftests/net/ipv6_fragmentation.c

0 → 100644
+114 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/*

 * Author: Brett A C Sheffield <bacs@librecast.net>

 *

 * Kernel selftest for the IPv6 fragmentation regression which affected stable

 * kernels:

 *

 *   https://lore.kernel.org/stable/aElivdUXqd1OqgMY@karahi.gladserv.com

 *

 * Commit: a18dfa9925b9 ("ipv6: save dontfrag in cork") was backported to stable

 * without some prerequisite commits.

 *

 * This caused a regression when sending IPv6 UDP packets by preventing

 * fragmentation and instead returning -1 (EMSGSIZE).

 *

 * This selftest demonstrates the issue by sending an IPv6 UDP packet to

 * localhost (::1) on the loopback interface from the autoconfigured link-local

 * address.

 *

 * sendmsg(2) returns bytes sent correctly on a working kernel, and returns -1

 * (EMSGSIZE) when the regression is present.

 *

 * The regression was not present in the mainline kernel, but add this test to

 * catch similar breakage in future.

 */



#define _GNU_SOURCE



#include <error.h>

#include <net/if.h>

#include <netinet/in.h>

#include <sched.h>

#include <stdio.h>

#include <sys/ioctl.h>

#include <sys/socket.h>

#include <unistd.h>

#include "../kselftest.h"



#define MTU 1500

#define LARGER_THAN_MTU 8192



static void setup(void)

{

	struct ifreq ifr = {

		.ifr_name = "lo"

	};

	int ctl;



	/* we need to set MTU, so do this in a namespace to play nicely */

	if (unshare(CLONE_NEWNET) == -1)

		error(KSFT_FAIL, errno, "unshare");



	ctl = socket(AF_LOCAL, SOCK_STREAM, 0);

	if (ctl == -1)

		error(KSFT_FAIL, errno, "socket");



	/* ensure MTU is smaller than what we plan to send */

	ifr.ifr_mtu = MTU;

	if (ioctl(ctl, SIOCSIFMTU, &ifr) == -1)

		error(KSFT_FAIL, errno, "ioctl: set MTU");



	/* bring up interface */

	if (ioctl(ctl, SIOCGIFFLAGS, &ifr) == -1)

		error(KSFT_FAIL, errno, "ioctl SIOCGIFFLAGS");

	ifr.ifr_flags = ifr.ifr_flags | IFF_UP;

	if (ioctl(ctl, SIOCSIFFLAGS, &ifr) == -1)

		error(KSFT_FAIL, errno, "ioctl: bring interface up");



	if (close(ctl) == -1)

		error(KSFT_FAIL, errno, "close");

}



int main(void)

{

	struct in6_addr addr = {

		.s6_addr[15] = 0x01,  /* ::1 */

	};

	struct sockaddr_in6 sa = {

		.sin6_family = AF_INET6,

		.sin6_addr = addr,

		.sin6_port = htons(9) /* port 9/udp (DISCARD) */

	};

	static char buf[LARGER_THAN_MTU] = {0};

	struct iovec iov = { .iov_base = buf, .iov_len = sizeof(buf) };

	struct msghdr msg = {

		.msg_iov = &iov,

		.msg_iovlen = 1,

		.msg_name = (struct sockaddr *)&sa,

		.msg_namelen = sizeof(sa),

	};

	ssize_t rc;

	int s;



	printf("Testing IPv6 fragmentation\n");

	setup();

	s = socket(AF_INET6, SOCK_DGRAM, 0);

send_again:

	rc = sendmsg(s, &msg, 0);

	if (rc == -1) {

		/* if interface wasn't ready, try again */

		if (errno == EADDRNOTAVAIL) {

			usleep(1000);

			goto send_again;

		}

		error(KSFT_FAIL, errno, "sendmsg");

	} else if (rc != LARGER_THAN_MTU) {

		error(KSFT_FAIL, errno, "sendmsg returned %zi, expected %i",

				rc, LARGER_THAN_MTU);

	}

	printf("[PASS] sendmsg() returned %zi\n", rc);

	if (close(s) == -1)

		error(KSFT_FAIL, errno, "close");

	return KSFT_PASS;

}