syzkaller/executor/common_linux.h

// Copyright 2016 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

// This file is shared between executor and csource package.

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include <sys/syscall.h>
#include <unistd.h>
#if defined(SYZ_EXECUTOR) || defined(SYZ_THREADED) || defined(SYZ_COLLIDE)
#include <pthread.h>
#include <stdlib.h>
#endif
#if defined(SYZ_EXECUTOR) || (defined(SYZ_REPEAT) && defined(SYZ_WAIT_REPEAT))
#include <errno.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <time.h>
#endif
#if defined(SYZ_EXECUTOR) || (defined(SYZ_REPEAT) && defined(SYZ_WAIT_REPEAT))
#include <sys/prctl.h>
#endif
#if defined(SYZ_EXECUTOR) || (defined(SYZ_REPEAT) && defined(SYZ_WAIT_REPEAT) && defined(SYZ_USE_TMP_DIR))
#include <dirent.h>
#include <sys/mount.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(SYZ_SANDBOX_NONE) || defined(SYZ_SANDBOX_SETUID) || defined(SYZ_SANDBOX_NAMESPACE)
#include <errno.h>
#include <sched.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <sys/prctl.h>
#include <sys/resource.h>
#include <sys/time.h>
#include <sys/wait.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(SYZ_SANDBOX_SETUID)
#include <grp.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(SYZ_SANDBOX_NAMESPACE)
#include <fcntl.h>
#include <linux/capability.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/stat.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(SYZ_TUN_ENABLE)
#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/if.h>
#include <linux/if_ether.h>
#include <linux/if_tun.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <net/if_arp.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(SYZ_FAULT_INJECTION)
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <sys/stat.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(__NR_syz_open_dev)
#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(__NR_syz_fuse_mount) || defined(__NR_syz_fuseblk_mount)
#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(__NR_syz_open_pts)
#include <fcntl.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#endif
#if defined(SYZ_EXECUTOR) || defined(__NR_syz_kvm_setup_cpu)
#include <errno.h>
#include <fcntl.h>
#include <linux/kvm.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#endif

#if defined(SYZ_EXECUTOR) || (defined(SYZ_REPEAT) && defined(SYZ_WAIT_REPEAT)) ||      \
    defined(SYZ_USE_TMP_DIR) || defined(SYZ_HANDLE_SEGV) || defined(SYZ_TUN_ENABLE) || \
    defined(SYZ_SANDBOX_NAMESPACE) || defined(SYZ_SANDBOX_SETUID) ||                   \
    defined(SYZ_SANDBOX_NONE) || defined(SYZ_FAULT_INJECTION) || defined(__NR_syz_kvm_setup_cpu)
// One does not simply exit.
// _exit can in fact fail.
// syzkaller did manage to generate a seccomp filter that prohibits exit_group syscall.
// Previously, we get into infinite recursion via segv_handler in such case
// and corrupted output_data, which does matter in our case since it is shared
// with fuzzer process. Loop infinitely instead. Parent will kill us.
// But one does not simply loop either. Compilers are sure that _exit never returns,
// so they remove all code after _exit as dead. Call _exit via volatile indirection.
// And this does not work as well. _exit has own handling of failing exit_group
// in the form of HLT instruction, it will divert control flow from our loop.
// So call the syscall directly.
__attribute__((noreturn)) static void doexit(int status)
{
	volatile unsigned i;
	syscall(__NR_exit_group, status);
	for (i = 0;; i++) {
	}
}
#define NORETURN __attribute__((noreturn))
#endif

#if defined(SYZ_EXECUTOR)
// exit/_exit do not necessary work.
#define exit use_doexit_instead
#define _exit use_doexit_instead
#endif

#include "common.h"

#if defined(SYZ_EXECUTOR) || defined(SYZ_HANDLE_SEGV)
static __thread int skip_segv;
static __thread jmp_buf segv_env;

static void segv_handler(int sig, siginfo_t* info, void* uctx)
{
	// Generated programs can contain bad (unmapped/protected) addresses,
	// which cause SIGSEGVs during copyin/copyout.
	// This handler ignores such crashes to allow the program to proceed.
	// We additionally opportunistically check that the faulty address
	// is not within executable data region, because such accesses can corrupt
	// output region and then fuzzer will fail on corrupted data.
	uintptr_t addr = (uintptr_t)info->si_addr;
	const uintptr_t prog_start = 1 << 20;
	const uintptr_t prog_end = 100 << 20;
	if (__atomic_load_n(&skip_segv, __ATOMIC_RELAXED) && (addr < prog_start || addr > prog_end)) {
		debug("SIGSEGV on %p, skipping\n", addr);
		_longjmp(segv_env, 1);
	}
	debug("SIGSEGV on %p, exiting\n", addr);
	doexit(sig);
	for (;;) {
	}
}

static void install_segv_handler()
{
	struct sigaction sa;

	// Don't need that SIGCANCEL/SIGSETXID glibc stuff.
	// SIGCANCEL sent to main thread causes it to exit
	// without bringing down the whole group.
	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = SIG_IGN;
	syscall(SYS_rt_sigaction, 0x20, &sa, NULL, 8);
	syscall(SYS_rt_sigaction, 0x21, &sa, NULL, 8);

	memset(&sa, 0, sizeof(sa));
	sa.sa_sigaction = segv_handler;
	sa.sa_flags = SA_NODEFER | SA_SIGINFO;
	sigaction(SIGSEGV, &sa, NULL);
	sigaction(SIGBUS, &sa, NULL);
}

#define NONFAILING(...)                                              \
	{                                                            \
		__atomic_fetch_add(&skip_segv, 1, __ATOMIC_SEQ_CST); \
		if (_setjmp(segv_env) == 0) {                        \
			__VA_ARGS__;                                 \
		}                                                    \
		__atomic_fetch_sub(&skip_segv, 1, __ATOMIC_SEQ_CST); \
	}
#endif

#if defined(SYZ_EXECUTOR) || (defined(SYZ_REPEAT) && defined(SYZ_WAIT_REPEAT))
static uint64_t current_time_ms()
{
	struct timespec ts;

	if (clock_gettime(CLOCK_MONOTONIC, &ts))
		fail("clock_gettime failed");
	return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}
#endif

#if defined(SYZ_EXECUTOR)
static void sleep_ms(uint64_t ms)
{
	usleep(ms * 1000);
}
#endif

#if defined(SYZ_EXECUTOR) || defined(SYZ_USE_TMP_DIR)
static void use_temporary_dir()
{
	char tmpdir_template[] = "./syzkaller.XXXXXX";
	char* tmpdir = mkdtemp(tmpdir_template);
	if (!tmpdir)
		fail("failed to mkdtemp");
	if (chmod(tmpdir, 0777))
		fail("failed to chmod");
	if (chdir(tmpdir))
		fail("failed to chdir");
}
#endif

#if defined(SYZ_EXECUTOR) || defined(SYZ_TUN_ENABLE)
static void vsnprintf_check(char* str, size_t size, const char* format, va_list args)
{
	int rv;

	rv = vsnprintf(str, size, format, args);
	if (rv < 0)
		fail("tun: snprintf failed");
	if ((size_t)rv >= size)
		fail("tun: string '%s...' doesn't fit into buffer", str);
}

static void snprintf_check(char* str, size_t size, const char* format, ...)
{
	va_list args;

	va_start(args, format);
	vsnprintf_check(str, size, format, args);
	va_end(args);
}

#define COMMAND_MAX_LEN 128

static void execute_command(const char* format, ...)
{
	va_list args;
	char command[COMMAND_MAX_LEN];
	int rv;

	va_start(args, format);

	vsnprintf_check(command, sizeof(command), format, args);
	rv = system(command);
	if (rv != 0)
		fail("tun: command \"%s\" failed with code %d", &command[0], rv);

	va_end(args);
}

static int tunfd = -1;
static int tun_frags_enabled;

// We just need this to be large enough to hold headers that we parse (ethernet/ip/tcp).
// Rest of the packet (if any) will be silently truncated which is fine.
#define SYZ_TUN_MAX_PACKET_SIZE 1000

// sysgen knowns about this constant (maxPids)
#define MAX_PIDS 32
#define ADDR_MAX_LEN 32

#define LOCAL_MAC "aa:aa:aa:aa:aa:%02hx"
#define REMOTE_MAC "bb:bb:bb:bb:bb:%02hx"

#define LOCAL_IPV4 "172.20.%d.170"
#define REMOTE_IPV4 "172.20.%d.187"

#define LOCAL_IPV6 "fe80::%02hxaa"
#define REMOTE_IPV6 "fe80::%02hxbb"

#ifndef IFF_NAPI
#define IFF_NAPI 0x0010
#endif
#ifndef IFF_NAPI_FRAGS
#define IFF_NAPI_FRAGS 0x0020
#endif

static void initialize_tun(uint64_t pid)
{
	if (pid >= MAX_PIDS)
		fail("tun: no more than %d executors", MAX_PIDS);
	int id = pid;

	tunfd = open("/dev/net/tun", O_RDWR | O_NONBLOCK);
	if (tunfd == -1)
		fail("tun: can't open /dev/net/tun");

	char iface[IFNAMSIZ];
	snprintf_check(iface, sizeof(iface), "syz%d", id);

	struct ifreq ifr;
	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, iface, IFNAMSIZ);
	ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_NAPI | IFF_NAPI_FRAGS;
	if (ioctl(tunfd, TUNSETIFF, (void*)&ifr) < 0) {
		// IFF_NAPI_FRAGS requires root, so try without it.
		ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
		if (ioctl(tunfd, TUNSETIFF, (void*)&ifr) < 0)
			fail("tun: ioctl(TUNSETIFF) failed");
	}
	// If IFF_NAPI_FRAGS is not supported it will be silently dropped,
	// so query the effective flags.
	if (ioctl(tunfd, TUNGETIFF, (void*)&ifr) < 0)
		fail("tun: ioctl(TUNGETIFF) failed");
	tun_frags_enabled = (ifr.ifr_flags & IFF_NAPI_FRAGS) != 0;
	debug("tun_frags_enabled=%d\n", tun_frags_enabled);

	char local_mac[ADDR_MAX_LEN];
	snprintf_check(local_mac, sizeof(local_mac), LOCAL_MAC, id);
	char remote_mac[ADDR_MAX_LEN];
	snprintf_check(remote_mac, sizeof(remote_mac), REMOTE_MAC, id);

	char local_ipv4[ADDR_MAX_LEN];
	snprintf_check(local_ipv4, sizeof(local_ipv4), LOCAL_IPV4, id);
	char remote_ipv4[ADDR_MAX_LEN];
	snprintf_check(remote_ipv4, sizeof(remote_ipv4), REMOTE_IPV4, id);

	char local_ipv6[ADDR_MAX_LEN];
	snprintf_check(local_ipv6, sizeof(local_ipv6), LOCAL_IPV6, id);
	char remote_ipv6[ADDR_MAX_LEN];
	snprintf_check(remote_ipv6, sizeof(remote_ipv6), REMOTE_IPV6, id);

	// Disable IPv6 DAD, otherwise the address remains unusable until DAD completes.
	execute_command("sysctl -w net.ipv6.conf.%s.accept_dad=0", iface);

	// Disable IPv6 router solicitation to prevent IPv6 spam.
	execute_command("sysctl -w net.ipv6.conf.%s.router_solicitations=0", iface);
	// There seems to be no way to disable IPv6 MTD to prevent more IPv6 spam.

	execute_command("ip link set dev %s address %s", iface, local_mac);
	execute_command("ip addr add %s/24 dev %s", local_ipv4, iface);
	execute_command("ip -6 addr add %s/120 dev %s", local_ipv6, iface);
	execute_command("ip neigh add %s lladdr %s dev %s nud permanent", remote_ipv4, remote_mac, iface);
	execute_command("ip -6 neigh add %s lladdr %s dev %s nud permanent", remote_ipv6, remote_mac, iface);
	execute_command("ip link set dev %s up", iface);
}

static void setup_tun(uint64_t pid, bool enable_tun)
{
	if (enable_tun)
		initialize_tun(pid);
}
#endif

#if defined(SYZ_EXECUTOR) || (defined(SYZ_TUN_ENABLE) && (defined(__NR_syz_extract_tcp_res) || defined(SYZ_REPEAT) && defined(SYZ_WAIT_REPEAT)))
static int read_tun(char* data, int size)
{
	int rv = read(tunfd, data, size);
	if (rv < 0) {
		if (errno == EAGAIN)
			return -1;
		// Tun sometimes returns this, unclear if it's a kernel bug or not.
		if (errno == EBADFD)
			return -1;
		fail("tun: read failed with %d", rv);
	}
	return rv;
}
#endif

#if defined(SYZ_EXECUTOR) || (defined(SYZ_DEBUG) && defined(SYZ_TUN_ENABLE) && (defined(__NR_syz_emit_ethernet) || defined(__NR_syz_extract_tcp_res)))
static void debug_dump_data(const char* data, int length)
{
	int i;
	for (i = 0; i < length; i++) {
		debug("%02hx ", (uint8_t)data[i] & (uint8_t)0xff);
		if (i % 16 == 15)
			debug("\n");
	}
	if (i % 16 != 0)
		debug("\n");
}
#endif

#if defined(SYZ_EXECUTOR) || (defined(__NR_syz_emit_ethernet) && defined(SYZ_TUN_ENABLE))
#define MAX_FRAGS 4
struct vnet_fragmentation {
	uint32_t full;
	uint32_t count;
	uint32_t frags[MAX_FRAGS];
};

static uintptr_t syz_emit_ethernet(uintptr_t a0, uintptr_t a1, uintptr_t a2)
{
	// syz_emit_ethernet(len len[packet], packet ptr[in, eth_packet], frags ptr[in, vnet_fragmentation, opt])
	// vnet_fragmentation {
	// 	full	int32[0:1]
	// 	count	len[frags, int32]
	// 	frags	array[int32[0:4096], 1:4]
	// }
	if (tunfd < 0)
		return (uintptr_t)-1;

	uint32_t length = a0;
	char* data = (char*)a1;
	debug_dump_data(data, length);

	struct vnet_fragmentation* frags = (struct vnet_fragmentation*)a2;
	struct iovec vecs[MAX_FRAGS + 1];
	uint32_t nfrags = 0;
	if (!tun_frags_enabled || frags == NULL) {
		vecs[nfrags].iov_base = data;
		vecs[nfrags].iov_len = length;
		nfrags++;
	} else {
		bool full = true;
		uint32_t i, count = 0;
		NONFAILING(full = frags->full);
		NONFAILING(count = frags->count);
		if (count > MAX_FRAGS)
			count = MAX_FRAGS;
		for (i = 0; i < count && length != 0; i++) {
			uint32_t size = 0;
			NONFAILING(size = frags->frags[i]);
			if (size > length)
				size = length;
			vecs[nfrags].iov_base = data;
			vecs[nfrags].iov_len = size;
			nfrags++;
			data += size;
			length -= size;
		}
		if (length != 0 && (full || nfrags == 0)) {
			vecs[nfrags].iov_base = data;
			vecs[nfrags].iov_len = length;
			nfrags++;
		}
	}
	return writev(tunfd, vecs, nfrags);
}
#endif

#if defined(SYZ_EXECUTOR) || (defined(SYZ_REPEAT) && defined(SYZ_WAIT_REPEAT) && defined(SYZ_TUN_ENABLE))
static void flush_tun()
{
	char data[SYZ_TUN_MAX_PACKET_SIZE];
	while (read_tun(&data[0], sizeof(data)) != -1)
		;
}
#endif

#if defined(SYZ_EXECUTOR) || (defined(__NR_syz_extract_tcp_res) && defined(SYZ_TUN_ENABLE))
#ifndef __ANDROID__
// Can't include <linux/ipv6.h>, since it causes
// conflicts due to some structs redefinition.
struct ipv6hdr {
	__u8 priority : 4,
	    version : 4;
	__u8 flow_lbl[3];

	__be16 payload_len;
	__u8 nexthdr;
	__u8 hop_limit;

	struct in6_addr saddr;
	struct in6_addr daddr;
};
#endif

struct tcp_resources {
	int32_t seq;
	int32_t ack;
};

static uintptr_t syz_extract_tcp_res(uintptr_t a0, uintptr_t a1, uintptr_t a2)
{
	// syz_extract_tcp_res(res ptr[out, tcp_resources], seq_inc int32, ack_inc int32)

	if (tunfd < 0)
		return (uintptr_t)-1;

	char data[SYZ_TUN_MAX_PACKET_SIZE];
	int rv = read_tun(&data[0], sizeof(data));
	if (rv == -1)
		return (uintptr_t)-1;
	size_t length = rv;
	debug_dump_data(data, length);

	struct tcphdr* tcphdr;

	if (length < sizeof(struct ethhdr))
		return (uintptr_t)-1;
	struct ethhdr* ethhdr = (struct ethhdr*)&data[0];

	if (ethhdr->h_proto == htons(ETH_P_IP)) {
		if (length < sizeof(struct ethhdr) + sizeof(struct iphdr))
			return (uintptr_t)-1;
		struct iphdr* iphdr = (struct iphdr*)&data[sizeof(struct ethhdr)];
		if (iphdr->protocol != IPPROTO_TCP)
			return (uintptr_t)-1;
		if (length < sizeof(struct ethhdr) + iphdr->ihl * 4 + sizeof(struct tcphdr))
			return (uintptr_t)-1;
		tcphdr = (struct tcphdr*)&data[sizeof(struct ethhdr) + iphdr->ihl * 4];
	} else {
		if (length < sizeof(struct ethhdr) + sizeof(struct ipv6hdr))
			return (uintptr_t)-1;
		struct ipv6hdr* ipv6hdr = (struct ipv6hdr*)&data[sizeof(struct ethhdr)];
		// TODO: parse and skip extension headers.
		if (ipv6hdr->nexthdr != IPPROTO_TCP)
			return (uintptr_t)-1;
		if (length < sizeof(struct ethhdr) + sizeof(struct ipv6hdr) + sizeof(struct tcphdr))
			return (uintptr_t)-1;
		tcphdr = (struct tcphdr*)&data[sizeof(struct ethhdr) + sizeof(struct ipv6hdr)];
	}

	struct tcp_resources* res = (struct tcp_resources*)a0;
	NONFAILING(res->seq = htonl((ntohl(tcphdr->seq) + (uint32_t)a1)));
	NONFAILING(res->ack = htonl((ntohl(tcphdr->ack_seq) + (uint32_t)a2)));

	debug("extracted seq: %08x\n", res->seq);
	debug("extracted ack: %08x\n", res->ack);

	return 0;
}
#endif

#if defined(SYZ_EXECUTOR) || defined(__NR_syz_open_dev)
static uintptr_t syz_open_dev(uintptr_t a0, uintptr_t a1, uintptr_t a2)
{
	if (a0 == 0xc || a0 == 0xb) {
		// syz_open_dev$char(dev const[0xc], major intptr, minor intptr) fd
		// syz_open_dev$block(dev const[0xb], major intptr, minor intptr) fd
		char buf[128];
		sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block", (uint8_t)a1, (uint8_t)a2);
		return open(buf, O_RDWR, 0);
	} else {
		// syz_open_dev(dev strconst, id intptr, flags flags[open_flags]) fd
		char buf[1024];
		char* hash;
		NONFAILING(strncpy(buf, (char*)a0, sizeof(buf)));
		buf[sizeof(buf) - 1] = 0;
		while ((hash = strchr(buf, '#'))) {
			*hash = '0' + (char)(a1 % 10); // 10 devices should be enough for everyone.
			a1 /= 10;
		}
		return open(buf, a2, 0);
	}
}
#endif

#if defined(SYZ_EXECUTOR) || defined(__NR_syz_open_pts)
static uintptr_t syz_open_pts(uintptr_t a0, uintptr_t a1)
{
	// syz_openpts(fd fd[tty], flags flags[open_flags]) fd[tty]
	int ptyno = 0;
	if (ioctl(a0, TIOCGPTN, &ptyno))
		return -1;
	char buf[128];
	sprintf(buf, "/dev/pts/%d", ptyno);
	return open(buf, a1, 0);
}
#endif

#if defined(SYZ_EXECUTOR) || defined(__NR_syz_fuse_mount)
static uintptr_t syz_fuse_mount(uintptr_t a0, uintptr_t a1, uintptr_t a2, uintptr_t a3, uintptr_t a4, uintptr_t a5)
{
	// syz_fuse_mount(target filename, mode flags[fuse_mode], uid uid, gid gid, maxread intptr, flags flags[mount_flags]) fd[fuse]
	uint64_t target = a0;
	uint64_t mode = a1;
	uint64_t uid = a2;
	uint64_t gid = a3;
	uint64_t maxread = a4;
	uint64_t flags = a5;

	int fd = open("/dev/fuse", O_RDWR);
	if (fd == -1)
		return fd;
	char buf[1024];
	sprintf(buf, "fd=%d,user_id=%ld,group_id=%ld,rootmode=0%o", fd, (long)uid, (long)gid, (unsigned)mode & ~3u);
	if (maxread != 0)
		sprintf(buf + strlen(buf), ",max_read=%ld", (long)maxread);
	if (mode & 1)
		strcat(buf, ",default_permissions");
	if (mode & 2)
		strcat(buf, ",allow_other");
	syscall(SYS_mount, "", target, "fuse", flags, buf);
	// Ignore errors, maybe fuzzer can do something useful with fd alone.
	return fd;
}
#endif

#if defined(SYZ_EXECUTOR) || defined(__NR_syz_fuseblk_mount)
static uintptr_t syz_fuseblk_mount(uintptr_t a0, uintptr_t a1, uintptr_t a2, uintptr_t a3, uintptr_t a4, uintptr_t a5, uintptr_t a6, uintptr_t a7)
{
	// syz_fuseblk_mount(target filename, blkdev filename, mode flags[fuse_mode], uid uid, gid gid, maxread intptr, blksize intptr, flags flags[mount_flags]) fd[fuse]
	uint64_t target = a0;
	uint64_t blkdev = a1;
	uint64_t mode = a2;
	uint64_t uid = a3;
	uint64_t gid = a4;
	uint64_t maxread = a5;
	uint64_t blksize = a6;
	uint64_t flags = a7;

	int fd = open("/dev/fuse", O_RDWR);
	if (fd == -1)
		return fd;
	if (syscall(SYS_mknodat, AT_FDCWD, blkdev, S_IFBLK, makedev(7, 199)))
		return fd;
	char buf[256];
	sprintf(buf, "fd=%d,user_id=%ld,group_id=%ld,rootmode=0%o", fd, (long)uid, (long)gid, (unsigned)mode & ~3u);
	if (maxread != 0)
		sprintf(buf + strlen(buf), ",max_read=%ld", (long)maxread);
	if (blksize != 0)
		sprintf(buf + strlen(buf), ",blksize=%ld", (long)blksize);
	if (mode & 1)
		strcat(buf, ",default_permissions");
	if (mode & 2)
		strcat(buf, ",allow_other");
	syscall(SYS_mount, blkdev, target, "fuseblk", flags, buf);
	// Ignore errors, maybe fuzzer can do something useful with fd alone.
	return fd;
}
#endif

#if defined(SYZ_EXECUTOR) || defined(__NR_syz_kvm_setup_cpu)
#if defined(__x86_64__)
#include "common_kvm_amd64.h"
#elif defined(__aarch64__)
#include "common_kvm_arm64.h"
#else
static uintptr_t syz_kvm_setup_cpu(uintptr_t a0, uintptr_t a1, uintptr_t a2, uintptr_t a3, uintptr_t a4, uintptr_t a5, uintptr_t a6, uintptr_t a7)
{
	return 0;
}
#endif
#endif // #ifdef __NR_syz_kvm_setup_cpu

#if defined(SYZ_EXECUTOR)
// TODO(dvyukov): syz_test call should be moved to a "test" target.
static uintptr_t syz_test()
{
	return 0;
}
#endif

#if defined(SYZ_EXECUTOR) || defined(SYZ_SANDBOX_NONE) || defined(SYZ_SANDBOX_SETUID) || defined(SYZ_SANDBOX_NAMESPACE)
static void loop();

static void sandbox_common()
{
	prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
	setpgrp();
	setsid();

	struct rlimit rlim;
	rlim.rlim_cur = rlim.rlim_max = 128 << 20;
	setrlimit(RLIMIT_AS, &rlim);
	rlim.rlim_cur = rlim.rlim_max = 8 << 20;
	setrlimit(RLIMIT_MEMLOCK, &rlim);
	rlim.rlim_cur = rlim.rlim_max = 1 << 20;
	setrlimit(RLIMIT_FSIZE, &rlim);
	rlim.rlim_cur = rlim.rlim_max = 1 << 20;
	setrlimit(RLIMIT_STACK, &rlim);
	rlim.rlim_cur = rlim.rlim_max = 0;
	setrlimit(RLIMIT_CORE, &rlim);

	// CLONE_NEWIPC/CLONE_IO cause EINVAL on some systems, so we do them separately of clone.
	unshare(CLONE_NEWNS);
	unshare(CLONE_NEWIPC);
	unshare(CLONE_IO);
}
#endif

#if defined(SYZ_EXECUTOR) || defined(SYZ_SANDBOX_NONE)
static int do_sandbox_none(int executor_pid, bool enable_tun)
{
	int pid = fork();
	if (pid)
		return pid;

	sandbox_common();
#if defined(SYZ_EXECUTOR) || defined(SYZ_TUN_ENABLE)
	setup_tun(executor_pid, enable_tun);
#endif

	loop();
	doexit(1);
}
#endif

#if defined(SYZ_EXECUTOR) || defined(SYZ_SANDBOX_SETUID)
static int do_sandbox_setuid(int executor_pid, bool enable_tun)
{
	int pid = fork();
	if (pid)
		return pid;

	sandbox_common();
#if defined(SYZ_EXECUTOR) || defined(SYZ_TUN_ENABLE)
	setup_tun(executor_pid, enable_tun);
#endif

	const int nobody = 65534;
	if (setgroups(0, NULL))
		fail("failed to setgroups");
	if (syscall(SYS_setresgid, nobody, nobody, nobody))
		fail("failed to setresgid");
	if (syscall(SYS_setresuid, nobody, nobody, nobody))
		fail("failed to setresuid");

	// This is required to open /proc/self/* files.
	// Otherwise they are owned by root and we can't open them after setuid.
	// See task_dump_owner function in kernel.
	prctl(PR_SET_DUMPABLE, 1, 0, 0, 0);

	loop();
	doexit(1);
}
#endif

#if defined(SYZ_EXECUTOR) || defined(SYZ_SANDBOX_NAMESPACE) || defined(SYZ_FAULT_INJECTION)
static bool write_file(const char* file, const char* what, ...)
{
	char buf[1024];
	va_list args;
	va_start(args, what);
	vsnprintf(buf, sizeof(buf), what, args);
	va_end(args);
	buf[sizeof(buf) - 1] = 0;
	int len = strlen(buf);

	int fd = open(file, O_WRONLY | O_CLOEXEC);
	if (fd == -1)
		return false;
	if (write(fd, buf, len) != len) {
		close(fd);
		return false;
	}
	close(fd);
	return true;
}
#endif

#if defined(SYZ_EXECUTOR) || defined(SYZ_SANDBOX_NAMESPACE)
static int real_uid;
static int real_gid;
__attribute__((aligned(64 << 10))) static char sandbox_stack[1 << 20];

static int namespace_sandbox_proc(void* arg)
{
	sandbox_common();

	// /proc/self/setgroups is not present on some systems, ignore error.
	write_file("/proc/self/setgroups", "deny");
	if (!write_file("/proc/self/uid_map", "0 %d 1\n", real_uid))
		fail("write of /proc/self/uid_map failed");
	if (!write_file("/proc/self/gid_map", "0 %d 1\n", real_gid))
		fail("write of /proc/self/gid_map failed");

	if (mkdir("./syz-tmp", 0777))
		fail("mkdir(syz-tmp) failed");
	if (mount("", "./syz-tmp", "tmpfs", 0, NULL))
		fail("mount(tmpfs) failed");
	if (mkdir("./syz-tmp/newroot", 0777))
		fail("mkdir failed");
	if (mkdir("./syz-tmp/newroot/dev", 0700))
		fail("mkdir failed");
	if (mount("/dev", "./syz-tmp/newroot/dev", NULL, MS_BIND | MS_REC | MS_PRIVATE, NULL))
		fail("mount(dev) failed");
	if (mkdir("./syz-tmp/newroot/proc", 0700))
		fail("mkdir failed");
	if (mount(NULL, "./syz-tmp/newroot/proc", "proc", 0, NULL))
		fail("mount(proc) failed");
	if (mkdir("./syz-tmp/pivot", 0777))
		fail("mkdir failed");
	if (syscall(SYS_pivot_root, "./syz-tmp", "./syz-tmp/pivot")) {
		debug("pivot_root failed");
		if (chdir("./syz-tmp"))
			fail("chdir failed");
	} else {
		if (chdir("/"))
			fail("chdir failed");
		if (umount2("./pivot", MNT_DETACH))
			fail("umount failed");
	}
	if (chroot("./newroot"))
		fail("chroot failed");
	if (chdir("/"))
		fail("chdir failed");

	// Drop CAP_SYS_PTRACE so that test processes can't attach to parent processes.
	// Previously it lead to hangs because the loop process stopped due to SIGSTOP.
	// Note that a process can always ptrace its direct children, which is enough
	// for testing purposes.
	struct __user_cap_header_struct cap_hdr = {};
	struct __user_cap_data_struct cap_data[2] = {};
	cap_hdr.version = _LINUX_CAPABILITY_VERSION_3;
	cap_hdr.pid = getpid();
	if (syscall(SYS_capget, &cap_hdr, &cap_data))
		fail("capget failed");
	cap_data[0].effective &= ~(1 << CAP_SYS_PTRACE);
	cap_data[0].permitted &= ~(1 << CAP_SYS_PTRACE);
	cap_data[0].inheritable &= ~(1 << CAP_SYS_PTRACE);
	if (syscall(SYS_capset, &cap_hdr, &cap_data))
		fail("capset failed");

	loop();
	doexit(1);
}

static int do_sandbox_namespace(int executor_pid, bool enable_tun)
{
#if defined(SYZ_EXECUTOR) || defined(SYZ_TUN_ENABLE)
	// For sandbox namespace we setup tun before dropping privs,
	// because IFF_NAPI_FRAGS requires root.
	setup_tun(executor_pid, enable_tun);
#endif

	real_uid = getuid();
	real_gid = getgid();
	mprotect(sandbox_stack, 4096, PROT_NONE); // to catch stack underflows
	return clone(namespace_sandbox_proc, &sandbox_stack[sizeof(sandbox_stack) - 64],
		     CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWUTS | CLONE_NEWNET, NULL);
}
#endif

#if defined(SYZ_EXECUTOR) || (defined(SYZ_REPEAT) && defined(SYZ_WAIT_REPEAT) && defined(SYZ_USE_TMP_DIR))
// One does not simply remove a directory.
// There can be mounts, so we need to try to umount.
// Moreover, a mount can be mounted several times, so we need to try to umount in a loop.
// Moreover, after umount a dir can become non-empty again, so we need another loop.
// Moreover, a mount can be re-mounted as read-only and then we will fail to make a dir empty.
static void remove_dir(const char* dir)
{
	DIR* dp;
	struct dirent* ep;
	int iter = 0;
retry:
	dp = opendir(dir);
	if (dp == NULL) {
		if (errno == EMFILE) {
			// This happens when the test process casts prlimit(NOFILE) on us.
			// Ideally we somehow prevent test processes from messing with parent processes.
			// But full sandboxing is expensive, so let's ignore this error for now.
			exitf("opendir(%s) failed due to NOFILE, exiting");
		}
		exitf("opendir(%s) failed", dir);
	}
	while ((ep = readdir(dp))) {
		if (strcmp(ep->d_name, ".") == 0 || strcmp(ep->d_name, "..") == 0)
			continue;
		char filename[FILENAME_MAX];
		snprintf(filename, sizeof(filename), "%s/%s", dir, ep->d_name);
		struct stat st;
		if (lstat(filename, &st))
			exitf("lstat(%s) failed", filename);
		if (S_ISDIR(st.st_mode)) {
			remove_dir(filename);
			continue;
		}
		int i;
		for (i = 0;; i++) {
			debug("unlink(%s)\n", filename);
			if (unlink(filename) == 0)
				break;
			if (errno == EROFS) {
				debug("ignoring EROFS\n");
				break;
			}
			if (errno != EBUSY || i > 100)
				exitf("unlink(%s) failed", filename);
			debug("umount(%s)\n", filename);
			if (umount2(filename, MNT_DETACH))
				exitf("umount(%s) failed", filename);
		}
	}
	closedir(dp);
	int i;
	for (i = 0;; i++) {
		debug("rmdir(%s)\n", dir);
		if (rmdir(dir) == 0)
			break;
		if (i < 100) {
			if (errno == EROFS) {
				debug("ignoring EROFS\n");
				break;
			}
			if (errno == EBUSY) {
				debug("umount(%s)\n", dir);
				if (umount2(dir, MNT_DETACH))
					exitf("umount(%s) failed", dir);
				continue;
			}
			if (errno == ENOTEMPTY) {
				if (iter < 100) {
					iter++;
					goto retry;
				}
			}
		}
		exitf("rmdir(%s) failed", dir);
	}
}
#endif

#if defined(SYZ_EXECUTOR) || defined(SYZ_FAULT_INJECTION)
static int inject_fault(int nth)
{
	int fd;
	char buf[128];

	sprintf(buf, "/proc/self/task/%d/fail-nth", (int)syscall(SYS_gettid));
	fd = open(buf, O_RDWR);
	if (fd == -1)
		fail("failed to open /proc/self/task/tid/fail-nth");
	sprintf(buf, "%d", nth + 1);
	if (write(fd, buf, strlen(buf)) != (ssize_t)strlen(buf))
		fail("failed to write /proc/self/task/tid/fail-nth");
	return fd;
}
#endif

#if defined(SYZ_EXECUTOR)
static int fault_injected(int fail_fd)
{
	char buf[16];
	int n = read(fail_fd, buf, sizeof(buf) - 1);
	if (n <= 0)
		fail("failed to read /proc/self/task/tid/fail-nth");
	int res = n == 2 && buf[0] == '0' && buf[1] == '\n';
	buf[0] = '0';
	if (write(fail_fd, buf, 1) != 1)
		fail("failed to write /proc/self/task/tid/fail-nth");
	close(fail_fd);
	return res;
}
#endif

#if defined(SYZ_REPEAT)
static void test();

#if defined(SYZ_WAIT_REPEAT)
void loop()
{
	int iter;
	for (iter = 0;; iter++) {
#ifdef SYZ_USE_TMP_DIR
		char cwdbuf[256];
		sprintf(cwdbuf, "./%d", iter);
		if (mkdir(cwdbuf, 0777))
			fail("failed to mkdir");
#endif
		int pid = fork();
		if (pid < 0)
			fail("clone failed");
		if (pid == 0) {
			prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
			setpgrp();
#ifdef SYZ_USE_TMP_DIR
			if (chdir(cwdbuf))
				fail("failed to chdir");
#endif
#ifdef SYZ_TUN_ENABLE
			flush_tun();
#endif
			test();
			doexit(0);
		}
		int status = 0;
		uint64_t start = current_time_ms();
		for (;;) {
			int res = waitpid(-1, &status, __WALL | WNOHANG);
			if (res == pid)
				break;
			usleep(1000);
			if (current_time_ms() - start > 5 * 1000) {
				kill(-pid, SIGKILL);
				kill(pid, SIGKILL);
				while (waitpid(-1, &status, __WALL) != pid) {
				}
				break;
			}
		}
#ifdef SYZ_USE_TMP_DIR
		remove_dir(cwdbuf);
#endif
	}
}
#else
void loop()
{
	while (1) {
		test();
	}
}
#endif
#endif