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
setup(void)42 static 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
main(void)73 int 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);
97 send_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 }
115