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 bacs@librecast.net Link: https://lore.kernel.org/stable/aElivdUXqd1OqgMY@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 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. 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; +}