Add selftest for the IPv6 fragmentation regression which affected
several stable kernels.
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).
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.
Signed-off-by: Brett A C Sheffield <b...@librecast.net>
Link: https://lore.kernel.org/stable/aelivduxqd1oq...@karahi.gladserv.com
---
tools/testing/selftests/net/.gitignore | 1 +
tools/testing/selftests/net/Makefile | 1 +
.../selftests/net/ipv6_fragmentation.c | 204 ++++++++++++++++++
3 files changed, 206 insertions(+)
create mode 100644 tools/testing/selftests/net/ipv6_fragmentation.c
diff --git a/tools/testing/selftests/net/.gitignore
b/tools/testing/selftests/net/.gitignore
index 47c293c2962f..3d4b4a53dfda 100644
--- a/tools/testing/selftests/net/.gitignore
+++ b/tools/testing/selftests/net/.gitignore
@@ -16,6 +16,7 @@ ip_local_port_range
ipsec
ipv6_flowlabel
ipv6_flowlabel_mgr
+ipv6_fragmentation
log.txt
msg_oob
msg_zerocopy
diff --git a/tools/testing/selftests/net/Makefile
b/tools/testing/selftests/net/Makefile
index b31a71f2b372..f83f91b758ae 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -117,6 +117,7 @@ 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
# YNL files, must be before "include ..lib.mk"
YNL_GEN_FILES := busy_poller netlink-dumps
diff --git a/tools/testing/selftests/net/ipv6_fragmentation.c
b/tools/testing/selftests/net/ipv6_fragmentation.c
new file mode 100644
index 000000000000..21e1a3cdc63d
--- /dev/null
+++ b/tools/testing/selftests/net/ipv6_fragmentation.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Author: Brett A C Sheffield <b...@librecast.net>
+ *
+ * Kernel selftest for the IPv6 fragmentation regression which affected
+ * stable kernels:
+ *
+ * https://lore.kernel.org/stable/aelivduxqd1oq...@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. sendmsg returns correctly (8192)
+ * 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 <fcntl.h>
+#include <linux/if_tun.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <sched.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#define MTU 1500
+#define LARGER_THAN_MTU 8192
+
+/* ensure MTU is smaller than what we plan to send */
+static int set_mtu(int ctl, char *ifname, struct ifreq *ifr)
+{
+ ifr->ifr_mtu = MTU;
+ return ioctl(ctl, SIOCSIFMTU, ifr);
+}
+
+/* bring up interface */
+static int interface_up(int ctl, char *ifname, struct ifreq *ifr)
+{
+ if (ioctl(ctl, SIOCGIFFLAGS, ifr) == -1) {
+ perror("ioctl SIOCGIFFLAGS");
+ return -1;
+ }
+ ifr->ifr_flags = ifr->ifr_flags | IFF_UP;
+ return ioctl(ctl, SIOCSIFFLAGS, ifr);
+}
+
+/* no need to wait for DAD in our namespace */
+static int disable_dad(char *ifname)
+{
+ char sysvar[] = "/proc/sys/net/ipv6/conf/%s/accept_dad";
+ char fname[IFNAMSIZ + sizeof(sysvar)];
+ int fd;
+
+ snprintf(fname, sizeof(fname), sysvar, ifname);
+ fd = open(fname, O_WRONLY);
+ if (fd == -1) {
+ perror("open accept_dad");
+ return -1;
+ }
+ if (write(fd, "0", 1) != 1) {
+ perror("write");
+ return -1;
+ }
+ return close(fd);
+}
+
+/* create TAP interface that will be deleted when this process exits */
+static int create_interface(int ctl, char *ifname, struct ifreq *ifr)
+{
+ int fd;
+
+ fd = open("/dev/net/tun", O_RDWR);
+ if (fd == -1) {
+ perror("open tun");
+ return -1;
+ }
+
+ ifr->ifr_flags = IFF_TAP | IFF_NO_PI;
+ if (ioctl(fd, TUNSETIFF, (void *)ifr) == -1) {
+ close(fd);
+ perror("ioctl: TUNSETIFF");
+ return -1;
+ }
+ strcpy(ifname, ifr->ifr_name);
+
+ return fd;
+}
+
+/* we need to set MTU, so do this in a namespace to play nicely */
+static int create_namespace(void)
+{
+ const char *netns_path = "/proc/self/ns/net";
+ int fd;
+
+ if (unshare(CLONE_NEWNET) != 0) {
+ perror("unshare");
+ return -1;
+ }
+
+ fd = open(netns_path, O_RDONLY);
+ if (fd == -1) {
+ perror("open");
+ return -1;
+ }
+
+ if (setns(fd, CLONE_NEWNET)) {
+ perror("setns");
+ return -1;
+ }
+
+ return 0;
+}
+
+static int setup(void)
+{
+ struct ifreq ifr = {0};
+ char ifname[IFNAMSIZ];
+ int fd = -1;
+ int ctl;
+
+ if (create_namespace() == -1)
+ return -1;
+
+ ctl = socket(AF_LOCAL, SOCK_STREAM, 0);
+ if (ctl == -1)
+ return -1;
+
+ memset(ifname, 0, sizeof(ifname));
+ fd = create_interface(ctl, ifname, &ifr);
+ if (fd == -1)
+ goto err_close_ctl;
+ if (disable_dad(ifname) == -1)
+ goto err_close_fd;
+ if (interface_up(ctl, ifname, &ifr) == -1)
+ goto err_close_fd;
+ if (set_mtu(ctl, ifname, &ifr) == -1)
+ goto err_close_fd;
+ usleep(10000); /* give interface a moment to wake up */
+ goto err_close_ctl;
+err_close_fd:
+ close(fd);
+ fd = -1;
+err_close_ctl:
+ close(ctl);
+ return fd;
+}
+
+int main(void)
+{
+ /* address doesn't matter, use an IPv6 multicast address for simplicity
*/
+ struct in6_addr addr = {
+ .s6_addr[0] = 0xff, /* multicast */
+ .s6_addr[1] = 0x12, /* set flags (T, link-local) */
+ };
+ struct sockaddr_in6 sa = {
+ .sin6_family = AF_INET6,
+ .sin6_addr = addr,
+ .sin6_port = 4242
+ };
+ 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 ns_fd;
+ int s;
+
+ printf("Testing IPv6 fragmentation\n");
+ ns_fd = setup();
+ if (ns_fd == -1)
+ return 1;
+ s = socket(AF_INET6, SOCK_DGRAM, 0);
+ msg.msg_name = (struct sockaddr *)&sa;
+ msg.msg_namelen = sizeof(sa);
+ rc = sendmsg(s, &msg, 0);
+ if (rc == -1) {
+ perror("send");
+ return 1;
+ } else if (rc != LARGER_THAN_MTU) {
+ fprintf(stderr, "send() returned %zi\n", rc);
+ return 1;
+ }
+ close(s);
+ close(ns_fd);
+
+ return 0;
+}
--
2.49.1
