// SPDX-License-Identifier: GPL-2.0 /* * Author: Brett A C Sheffield * * 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 #include #include #include #include #include #include #include #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; }