Debianize.

[preload-hacks] / noip.c

#define _GNU_SOURCE
#undef sun
#undef SUN
#define DEBUG

#include <ctype.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

#include <unistd.h>
#include <dirent.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <pwd.h>

#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>

#include <netinet/in.h>
#include <arpa/inet.h>
#include <netinet/tcp.h>
#include <netinet/udp.h>
#include <net/if.h>

enum { UNUSED, STALE, USED };
enum { WANT_FRESH, WANT_EXISTING };
enum { DENY, ALLOW };
typedef struct aclnode {
  struct aclnode *next;
  int act;
  unsigned long minaddr, maxaddr;
  unsigned short minport, maxport;
} aclnode;

#define MAX_LOCAL_IPADDRS 16
static struct in_addr local_ipaddrs[MAX_LOCAL_IPADDRS];
static int n_local_ipaddrs;

static uid_t uid;
static char *sockdir = 0;
static int debug = 0;

static aclnode *bind_real, **bind_tail = &bind_real;
static aclnode *connect_real,  **connect_tail = &connect_real;

/* --- Import magic --- */

#define IMPORTS(_)							\
  _(socket, int, (int, int, int))					\
  _(socketpair, int, (int, int, int, int *))				\
  _(connect, int, (int, const struct sockaddr *, socklen_t))		\
  _(bind, int, (int, const struct sockaddr *, socklen_t))		\
  _(accept, int, (int, struct sockaddr *, socklen_t *))			\
  _(getsockname, int, (int, struct sockaddr *, socklen_t *))		\
  _(getpeername, int, (int, struct sockaddr *, socklen_t *))		\
  _(getsockopt, int, (int, int, int, void *, socklen_t *))		\
  _(setsockopt, int, (int, int, int, const void *, socklen_t))		\
  _(sendto, ssize_t, (int, const void *buf, size_t, int,		\
		      const struct sockaddr *to, socklen_t tolen))	\
  _(recvfrom, ssize_t, (int, void *buf, size_t, int,			\
		        struct sockaddr *from, socklen_t *fromlen))	\
  _(sendmsg, ssize_t, (int, const struct msghdr *, int))		\
  _(recvmsg, ssize_t, (int, struct msghdr *, int))			\
  _(close, int, (int))

#define DECL(imp, ret, args) static ret (*real_##imp) args;
IMPORTS(DECL)
#undef DECL

static void setup(void) __attribute__((constructor));
static void import(void)
{
#define IMPORT(imp, ret, args)						\
    real_##imp = (ret (*)args)dlsym(RTLD_NEXT, #imp);
  IMPORTS(IMPORT)
#undef IMPORT
}

/* --- Support --- */

#define SA(sa) ((struct sockaddr *)(sa))
#define SIN(sa) ((struct sockaddr_in *)(sa))
#define SUN(sa) ((struct sockaddr_un *)(sa))

#define UC(ch) ((unsigned char)(ch))

#define NEW(x) ((x) = xmalloc(sizeof(*x)))
#define NEWV(x, n) ((x) = xmalloc(sizeof(*x) * (n)))

#ifdef DEBUG
#  define D(body) { if (debug) { body } }
#else
#  define D(body) ;
#endif

#define PRESERVING_ERRNO(body) do {					\
  int _err = errno; { body } errno = _err;				\
} while (0)

static void *xmalloc(size_t n)
{
  void *p;
  if (!n) return (0);
  if ((p = malloc(n)) == 0) { perror("malloc"); exit(1); }
  return (p);
}

static char *xstrdup(const char *p)
{
  size_t n = strlen(p) + 1;
  char *q = xmalloc(n);
  memcpy(q, p, n);
  return (q);
}

static int unix_socket_status(struct sockaddr_un *sun, int quick_p)
{
  struct stat st;
  FILE *fp = 0;
  size_t len, n;
  int rc;
  char buf[256];

  rc = UNUSED;
  if (stat(sun->sun_path, &st) && errno == ENOENT)
    goto done;
  rc = USED;
  if (quick_p)
    goto done;

  if ((fp = fopen("/proc/net/unix", "r")) == 0)
    goto done;
  fgets(buf, sizeof(buf), fp); /* skip header */
  len = strlen(sun->sun_path);
  while (fgets(buf, sizeof(buf), fp)) {
    n = strlen(buf);
    if (n >= len + 2 && buf[n - len - 2] == ' ' && buf[n - 1] == '\n' &&
	memcmp(buf + n - len - 1, sun->sun_path, len) == 0)
      goto done;
  }
  if (ferror(fp))
    goto done;
  rc = STALE;
done:
  if (fp) fclose(fp);
  return (rc);
}

#ifdef DEBUG

static void dump_aclnode(aclnode *a)
{
  char minbuf[16], maxbuf[16];
  struct in_addr amin, amax;

  amin.s_addr = htonl(a->minaddr);
  amax.s_addr = htonl(a->maxaddr);
  fprintf(stderr, "noip:   %c ", a->act ? '+' : '-');
  if (a->minaddr == 0 && a->maxaddr == 0xffffffff)
    fprintf(stderr, "any");
  else {
    fprintf(stderr, "%s",
	    inet_ntop(AF_INET, &amin, minbuf, sizeof(minbuf)));
    if (a->maxaddr != a->minaddr) {
      fprintf(stderr, "-%s",
	      inet_ntop(AF_INET, &amax, maxbuf, sizeof(maxbuf)));
    }
  }
  if (a->minport != 0 || a->maxport != 0xffff) {
    fprintf(stderr, ":%u", (unsigned)a->minport);
    if (a->minport != a->maxport)
      fprintf(stderr, "-%u", (unsigned)a->maxport);
  }
  fputc('\n', stderr);
}

#endif

static int acl_allows_p(aclnode *a, const struct sockaddr_in *sin)
{
  unsigned long addr = ntohl(sin->sin_addr.s_addr);
  unsigned short port = ntohs(sin->sin_port);
  int act = ALLOW;

  D( char buf[16];
     fprintf(stderr, "noip: check %s:%u\n",
	     inet_ntop(AF_INET, &sin->sin_addr, buf, sizeof(buf)),
	     ntohs((unsigned)sin->sin_port)); )
  for (; a; a = a->next) {
    D( dump_aclnode(a); )
    if (a->minaddr <= addr && addr <= a->maxaddr &&
	a->minport <= port && port <= a->maxport) {
      D( fprintf(stderr, "noip: aha!  %s\n", a->act ? "ALLOW" : "DENY"); )
      return (a->act);
    }
    act = a->act;
  }
  D( fprintf(stderr, "noip: nothing found: %s\n", act ? "DENY" : "ALLOW"); )
  return (!act);
}

#ifdef DEBUG

static void dump_acl(aclnode *a)
{
  int act = ALLOW;
  
  for (; a; a = a->next) {
    dump_aclnode(a);
    act = a->act;
  }
  fprintf(stderr, "noip:   [default policy: %s]\n",
	  act == ALLOW ? "DENY" : "ALLOW");
}

#endif

static int encode_inet_addr(struct sockaddr_un *sun,
			    const struct sockaddr_in *sin,
			    int want)
{
  int i;
  int desperate_p = 0;
  char buf[INET_ADDRSTRLEN];
  int rc;

  D( fprintf(stderr, "noip: encode %s:%u (%s)",
	     inet_ntop(AF_INET, &sin->sin_addr, buf, sizeof(buf)),
	     (unsigned)ntohs(sin->sin_port),
	     want == WANT_EXISTING ? "EXISTING" : "FRESH"); )
  sun->sun_family = AF_UNIX;
  if (sin->sin_port || want == WANT_EXISTING) {
    snprintf(sun->sun_path, sizeof(sun->sun_path), "%s/%s:%u", sockdir,
	     inet_ntop(AF_INET, &sin->sin_addr, buf, sizeof(buf)),
	     (unsigned)ntohs(sin->sin_port));
    rc = unix_socket_status(sun, 0);
    if (rc == STALE) unlink(sun->sun_path);
    if (rc != USED && want == WANT_EXISTING) {
      snprintf(sun->sun_path, sizeof(sun->sun_path), "%s/0.0.0.0:%u",
	       sockdir, (unsigned)ntohs(sin->sin_port));
      if (unix_socket_status(sun, 0) == STALE) unlink(sun->sun_path);
    }
  } else {
    for (desperate_p = 0; desperate_p < 2; desperate_p++) {
      for (i = 16384; i < 65536; i++) {
	snprintf(sun->sun_path, sizeof(sun->sun_path), "%s/%s:%u", sockdir,
		 inet_ntop(AF_INET, &sin->sin_addr, buf, sizeof(buf)),
		 (unsigned)i);
	rc = unix_socket_status(sun, !desperate_p);
	switch (rc) {
	  case STALE: unlink(sun->sun_path);
	  case UNUSED: goto found;
	}
      }
    }
    errno = EADDRINUSE;
    D( fprintf(stderr, " -- can't resolve\n"); )
    return (-1);
  found:;
  }
  D( fprintf(stderr, " -> `%s'\n", sun->sun_path); )
  return (0);
}

static int decode_inet_addr(struct sockaddr_in *sin,
			    const struct sockaddr_un *sun,
			    socklen_t len)
{
  char buf[INET_ADDRSTRLEN + 16];
  char *p;
  size_t n = strlen(sockdir), nn = strlen(sun->sun_path);
  struct sockaddr_in sin_mine;
  unsigned long port;

  if (!sin)
    sin = &sin_mine;
  if (sun->sun_family != AF_UNIX)
    return (-1);
  if (len < sizeof(sun)) ((char *)sun)[len] = 0;
  D( fprintf(stderr, "noip: decode (%d) `%s'",
	     *sun->sun_path, sun->sun_path); )
  if (!sun->sun_path[0]) {
    sin->sin_family = AF_INET;
    sin->sin_addr.s_addr = INADDR_ANY;
    sin->sin_port = 0;
    D( fprintf(stderr, " -- unbound socket\n"); )
    return (0);
  }
  if (nn < n + 1 || nn - n >= sizeof(buf) || sun->sun_path[n] != '/' ||
      memcmp(sun->sun_path, sockdir, n) != 0) {
    D( fprintf(stderr, " -- not one of ours\n"); )
    return (-1);
  }
  memcpy(buf, sun->sun_path + n + 1, nn - n);
  if ((p = strchr(buf, ':')) == 0) {
    D( fprintf(stderr, " -- malformed (no port)\n"); )
    return (-1);
  }
  *p++ = 0;
  sin->sin_family = AF_INET;
  if (inet_pton(AF_INET, buf, &sin->sin_addr) <= 0) {
    D( fprintf(stderr, " -- malformed (bad address `%s')\n", buf); )
    return (-1);
  }
  port = strtoul(p, &p, 10);
  if (*p || port >= 65536) {
    D( fprintf(stderr, " -- malformed (port out of range)"); )
    return (-1);
  }
  sin->sin_port = htons(port);
  D( fprintf(stderr, " -> %s:%u\n",
	     inet_ntop(AF_INET, &sin->sin_addr, buf, sizeof(buf)),
	     (unsigned)port); )
  return (0);
}

static int fixup_real_ip_socket(int sk)
{
  int nsk;
  int type;
  int f, fd;
  struct sockaddr_un sun;
  struct sockaddr_in sin;
  socklen_t len;

#define OPTS(_)								\
  _(DEBUG, int)								\
  _(REUSEADDR, int)							\
  _(DONTROUTE, int)							\
  _(BROADCAST, int)							\
  _(SNDBUF, int)							\
  _(RCVBUF, int)							\
  _(OOBINLINE, int)							\
  _(NO_CHECK, int)							\
  _(LINGER, struct linger)						\
  _(BSDCOMPAT, int)							\
  _(RCVLOWAT, int)							\
  _(RCVTIMEO, struct timeval)						\
  _(SNDTIMEO, struct timeval)

  len = sizeof(sun);
  if (real_getsockname(sk, SA(&sun), &len))
    return (-1);
  if (decode_inet_addr(&sin, &sun, len))
    return (0); /* Not one of ours */
  len = sizeof(type);
  if (real_getsockopt(sk, SOL_SOCKET, SO_TYPE, &type, &len) < 0 ||
      (nsk = real_socket(PF_INET, type, 0)) < 0)
    return (-1);
#define FIX(opt, ty) do {						\
  ty ov_;								\
  len = sizeof(ov_);							\
  if (real_getsockopt(sk, SOL_SOCKET, SO_##opt, &ov_, &len) < 0 ||	\
      real_setsockopt(nsk, SOL_SOCKET, SO_##opt, &ov_, len)) {		\
    real_close(nsk);							\
    return (-1);							\
  }									\
} while (0);
  OPTS(FIX)
#undef FIX
  if ((f = fcntl(sk, F_GETFL)) < 0 ||
      (fd = fcntl(sk, F_GETFD)) < 0 ||
      fcntl(nsk, F_SETFL, f) < 0 ||
      dup2(nsk, sk) < 0) {
    real_close(nsk);
    return (-1);
  }
  unlink(sun.sun_path);
  real_close(nsk);
  if (fcntl(sk, F_SETFD, fd) < 0) {
    perror("noip: fixup_real_ip_socket F_SETFD");
    abort();
  }
  return (0);
}

static int do_implicit_bind(int sk, const struct sockaddr **sa,
			    socklen_t *len, struct sockaddr_un *sun)
{
  struct sockaddr_in sin;
  socklen_t mylen = sizeof(*sun);

  if (acl_allows_p(connect_real, SIN(*sa))) {
    if (fixup_real_ip_socket(sk))
      return (-1);
  } else {
    if (real_getsockname(sk, SA(sun), &mylen) < 0)
      return (-1);
    if (sun->sun_family == AF_UNIX) {
      if (mylen < sizeof(*sun)) ((char *)sun)[mylen] = 0;
      if (!sun->sun_path[0]) {
	sin.sin_family = AF_INET;
	sin.sin_addr.s_addr = INADDR_LOOPBACK;
	sin.sin_port = 0;
	encode_inet_addr(sun, &sin, WANT_FRESH);
	if (real_bind(sk, SA(sun), SUN_LEN(sun)))
	  return (-1);
      }
      encode_inet_addr(sun, SIN(*sa), WANT_EXISTING);
      *sa = SA(sun);
      *len = SUN_LEN(sun);
    }
  }
  return (0);
}

static void return_fake_name(struct sockaddr *sa, socklen_t len,
			     struct sockaddr *fake, socklen_t *fakelen)
{
  struct sockaddr_in sin;
  socklen_t alen;

  if (sa->sa_family == AF_UNIX && !decode_inet_addr(&sin, SUN(sa), len)) {
    sa = SA(&sin);
    len = sizeof(sin);
  }
  alen = len;
  if (len > *fakelen)
    len = *fakelen;
  if (len > 0)
    memcpy(fake, sa, len);
  *fakelen = alen;
}

/* --- Configuration --- */

static char *home(void)
{
  char *p;
  struct passwd *pw;

  if ((p = getenv("HOME")) != 0) return (p);
  else if ((pw = getpwuid(uid)) != 0) return (pw->pw_dir);
  else return "/notexist";
}

static char *tmpdir(void)
{
  char *p;

  if ((p = getenv("TMPDIR")) != 0) return (p);
  else if ((p = getenv("TMP")) != 0) return (p);
  else return ("/tmp");
}

static char *user(void)
{
  static char buf[16];
  char *p;
  struct passwd *pw;

  if ((p = getenv("USER")) != 0) return (p);
  else if ((p = getenv("LOGNAME")) != 0) return (p);
  else if ((pw = getpwuid(uid)) != 0) return (pw->pw_name);
  else {
    snprintf(buf, sizeof(buf), "uid-%lu", (unsigned long)uid);
    return (buf);
  }
}

#define SKIPSPC do { while (*p && isspace(UC(*p))) p++; } while (0)
#define NEXTWORD(q) do {						\
  SKIPSPC;								\
  q = p;								\
  while (*p && !isspace(UC(*p))) p++;					\
  if (*p) *p++ = 0;							\
} while (0)
#define NEXTADDR(q, del) do {						\
  SKIPSPC;								\
  q = p;								\
  while (*p && (*p == '.' || isdigit(UC(*p)))) p++;			\
  del = *p;								\
  if (*p) *p++ = 0;							\
} while (0)
#define NEXTNUMBER(q, del) do {						\
  SKIPSPC;								\
  q = p;								\
  while (*p && isdigit(UC(*p))) p++;					\
  del = *p;								\
  if (*p) *p++ = 0;							\
} while (0)
#define RESCAN(del) do { if (del) *--p = del; } while (0)
#define KWMATCHP(kw) (strncmp(p, kw, sizeof(kw) - 1) == 0 &&		\
		      !isalnum(UC(p[sizeof(kw) - 1])) &&		\
		      (p += sizeof(kw) - 1))
  
static void parse_ports(char **pp, unsigned short *min, unsigned short *max)
{
  char *p = *pp, *q;
  int del;

  SKIPSPC;
  if (*p != ':') {
    *min = 0;
    *max = 0xffff;
  } else {
    p++;
    NEXTNUMBER(q, del);
    *min = atoi(q);
    RESCAN(del);
    SKIPSPC;
    if (*p == '-') {
      NEXTNUMBER(q, del);
      *max = atoi(q);
      RESCAN(del);
    } else
      *max = *min;
  }
  *pp = p;
}

#define ACLNODE(tail_, act_,						\
		minaddr_, maxaddr_, minport_, maxport_) do {		\
  aclnode *a_;								\
  NEW(a_);								\
  a_->act = act_;							\
  a_->minaddr = minaddr_; a_->maxaddr = maxaddr_;			\
  a_->minport = minport_; a_->maxport = maxport_;			\
  *tail_ = a_; tail_ = &a_->next;					\
} while (0)

static void parse_acl_line(char **pp, aclnode ***tail)
{
  struct in_addr addr;
  unsigned long minaddr, maxaddr, mask;
  unsigned short minport, maxport;
  int i, n;
  int act;
  int del;
  char *p = *pp;
  char *q;

  SKIPSPC;
  if (*p == '+') act = ALLOW;
  else if (*p == '-') act = DENY;
  else goto bad;

  p++;
  SKIPSPC;
  if (KWMATCHP("any")) {
    minaddr = 0;
    maxaddr = 0xffffffff;
    goto justone;
  } else if (KWMATCHP("local")) {
    parse_ports(&p, &minport, &maxport);
    ACLNODE(*tail, act, 0, 0, minport, maxport);
    ACLNODE(*tail, act, 0xffffffff, 0xffffffff, minport, maxport);
    for (i = 0; i < n_local_ipaddrs; i++) {
      minaddr = ntohl(local_ipaddrs[i].s_addr);
      ACLNODE(*tail, act, minaddr, minaddr, minport, maxport);
    }
  } else {
    if (*p == ':') {
      minaddr = 0;
      maxaddr = 0xffffffff;
    } else {
      NEXTADDR(q, del);
      if (inet_pton(AF_INET, q, &addr) <= 0) goto bad;
      minaddr = ntohl(addr.s_addr);
      RESCAN(del);
      SKIPSPC;
      if (*p == '-') {
	p++;
	NEXTADDR(q, del);
	if (inet_pton(AF_INET, q, &addr) <= 0) goto bad;
	RESCAN(del);
	maxaddr = ntohl(addr.s_addr);
      } else if (*p == '/') {
	p++;
	NEXTADDR(q, del);
	if (strchr(q, '.')) {
	  if (inet_pton(AF_INET, q, &addr) <= 0) goto bad;
	  mask = ntohl(addr.s_addr);
	} else {
	  n = atoi(q);
	  mask = (~0ul << (32 - n)) & 0xffffffff;
	}
	RESCAN(del);
	minaddr &= mask;
	maxaddr = minaddr | (mask ^ 0xffffffff);
      } else
	maxaddr = minaddr;
    }
  justone:
    parse_ports(&p, &minport, &maxport);
    ACLNODE(*tail, act, minaddr, maxaddr, minport, maxport);
  }
  return;

bad:
  D( fprintf(stderr, "noip: bad acl spec (ignored)\n"); )
  return;
}

static void readconfig(void)
{
  FILE *fp;
  char buf[1024];
  size_t n;
  char *p, *cmd;

  if ((p = getenv("NOIP_CONFIG")) == 0)
    snprintf(p = buf, sizeof(buf), "%s/.noip", home());
  D( fprintf(stderr, "noip: config file: %s\n", p); )
  if ((fp = fopen(p, "r")) == 0)
    goto done;

  while (fgets(buf, sizeof(buf), fp)) {
    n = strlen(buf);
    p = buf;

    SKIPSPC;
    if (!*p || *p == '#') continue;
    while (n && isspace(UC(buf[n - 1]))) n--;
    buf[n] = 0;
    NEXTWORD(cmd);
    SKIPSPC;

    if (strcmp(cmd, "socketdir") == 0)
      sockdir = xstrdup(p);
    else if (strcmp(cmd, "realbind") == 0)
      parse_acl_line(&p, &bind_tail);
    else if (strcmp(cmd, "realconnect") == 0)
      parse_acl_line(&p, &connect_tail);
    else if (strcmp(cmd, "debug") == 0)
      debug = *p ? atoi(p) : 1;
    else
      D( fprintf(stderr, "noip: bad config command %s\n", cmd); )
  }
  fclose(fp);

done:
  *bind_tail = 0;
  *connect_tail = 0;
  if (!sockdir) {
    snprintf(buf, sizeof(buf), "%s/noip-%s", tmpdir(), user());
    sockdir = xstrdup(buf);
  }
  D( fprintf(stderr, "noip: sockdir: %s\n", sockdir);
     fprintf(stderr, "noip: realbind acl:\n");
     dump_acl(bind_real);
     fprintf(stderr, "noip: realconnect acl:\n");
     dump_acl(connect_real); )
}

/* --- Hooks --- */

int socket(int pf, int ty, int proto)
{
  if (pf == PF_INET) {
    pf = PF_UNIX;
    proto = 0;
  }
  return real_socket(pf, ty, proto);
}

int socketpair(int pf, int ty, int proto, int *sk)
{
  if (pf == PF_INET) {
    pf = PF_UNIX;
    proto = 0;
  }
  return (real_socketpair(pf, ty, proto, sk));
}

int bind(int sk, const struct sockaddr *sa, socklen_t len)
{
  struct sockaddr_un sun;

  if (sa->sa_family == AF_INET) { 
    PRESERVING_ERRNO({
      if (acl_allows_p(bind_real, SIN(sa))) {
	if (fixup_real_ip_socket(sk))
	  return (-1);
      } else {
	encode_inet_addr(&sun, SIN(sa), WANT_FRESH);
	sa = SA(&sun);
	len = SUN_LEN(&sun);
      }
    });
  }
  return real_bind(sk, sa, len);
}

int connect(int sk, const struct sockaddr *sa, socklen_t len)
{
  struct sockaddr_un sun;

  if (sa->sa_family == AF_INET) {
    PRESERVING_ERRNO({
      do_implicit_bind(sk, &sa, &len, &sun);
    });
  }
  return real_connect(sk, sa, len);
}

ssize_t sendto(int sk, const void *buf, size_t len, int flags,
	       const struct sockaddr *to, socklen_t tolen)
{
  struct sockaddr_un sun;

  if (to && to->sa_family == AF_INET) {
    PRESERVING_ERRNO({
      do_implicit_bind(sk, &to, &tolen, &sun);
    });
  }
  return real_sendto(sk, buf, len, flags, to, tolen);
}

ssize_t recvfrom(int sk, void *buf, size_t len, int flags,
		 struct sockaddr *from, socklen_t *fromlen)
{
  char sabuf[1024];
  socklen_t mylen = sizeof(sabuf);
  ssize_t n;

  if (!from)
    return real_recvfrom(sk, buf, len, flags, 0, 0);
  PRESERVING_ERRNO({
    n = real_recvfrom(sk, buf, len, flags, SA(sabuf), &mylen);
    if (n < 0)
      return (-1);
    return_fake_name(SA(sabuf), mylen, from, fromlen);
  });
  return (n);
}

ssize_t sendmsg(int sk, const struct msghdr *msg, int flags)
{
  struct sockaddr_un sun;
  const struct sockaddr *sa;
  struct msghdr mymsg;

  if (msg->msg_name && SA(msg->msg_name)->sa_family == AF_INET) {
    PRESERVING_ERRNO({
      sa = SA(msg->msg_name);
      mymsg = *msg;
      do_implicit_bind(sk, &sa, &mymsg.msg_namelen, &sun);
      mymsg.msg_name = SA(sa);
      msg = &mymsg;
    });
  }
  return real_sendmsg(sk, msg, flags);
}

ssize_t recvmsg(int sk, struct msghdr *msg, int flags)
{
  char sabuf[1024];
  struct sockaddr *sa;
  socklen_t len;
  ssize_t n;

  if (!msg->msg_name)
    return real_recvmsg(sk, msg, flags);
  PRESERVING_ERRNO({
    sa = SA(msg->msg_name);
    len = msg->msg_namelen;
    msg->msg_name = sabuf;
    msg->msg_namelen = sizeof(sabuf);
    n = real_recvmsg(sk, msg, flags);
    if (n < 0)
      return (-1);
    return_fake_name(SA(sabuf), msg->msg_namelen, sa, &len);
    msg->msg_name = sa;
    msg->msg_namelen = len;
  });
  return (n);
}

int accept(int sk, struct sockaddr *sa, socklen_t *len)
{
  char sabuf[1024];
  socklen_t mylen = sizeof(sabuf);
  int nsk = real_accept(sk, SA(sabuf), &mylen);

  if (nsk < 0)
    return (-1);
  return_fake_name(SA(sabuf), mylen, sa, len);
  return (nsk);
}

int getsockname(int sk, struct sockaddr *sa, socklen_t *len)
{
  PRESERVING_ERRNO({
    char sabuf[1024];
    socklen_t mylen = sizeof(sabuf);
    if (real_getsockname(sk, SA(sabuf), &mylen))
      return (-1);
    return_fake_name(SA(sabuf), mylen, sa, len);
  });
  return (0);
}

int getpeername(int sk, struct sockaddr *sa, socklen_t *len)
{
  PRESERVING_ERRNO({
    char sabuf[1024];
    socklen_t mylen = sizeof(sabuf);
    if (real_getpeername(sk, SA(sabuf), &mylen))
      return (-1);
    return_fake_name(SA(sabuf), mylen, sa, len);
  });
  return (0);
}

int getsockopt(int sk, int lev, int opt, void *p, socklen_t *len)
{
  switch (lev) {
    case SOL_IP:
    case SOL_TCP:
    case SOL_UDP:
      if (*len > 0)
	memset(p, 0, *len);
      return (0);
  }
  return real_getsockopt(sk, lev, opt, p, len);
}

int setsockopt(int sk, int lev, int opt, const void *p, socklen_t len)
{
  switch (lev) {
    case SOL_IP:
    case SOL_TCP:
    case SOL_UDP:
      return (0);
  }
  switch (opt) {
    case SO_BINDTODEVICE:
    case SO_ATTACH_FILTER:
    case SO_DETACH_FILTER:
      return (0);
  }
  return real_setsockopt(sk, lev, opt, p, len);
}

/* --- Initialization --- */

static void cleanup_sockdir(void)
{
  DIR *dir;
  struct dirent *d;
  struct sockaddr_un sun;

  if ((dir = opendir(sockdir)) == 0)
    return;
  while ((d = readdir(dir)) != 0) {
    if (d->d_name[0] == '.') continue;
    snprintf(sun.sun_path, sizeof(sun.sun_path),
	     "%s/%s", sockdir, d->d_name);
    if (unix_socket_status(&sun, 0) == STALE) {
      D( fprintf(stderr, "noip: clearing away stale socket %s\n",
		 d->d_name); )
      unlink(sun.sun_path);
    }
  }
  closedir(dir);
}

static void get_local_ipaddrs(void)
{
  struct if_nameindex *ifn;
  struct ifreq ifr;
  int sk;
  int i;

  ifn = if_nameindex();
  if ((sk = real_socket(PF_INET, SOCK_STREAM, 00)) < 0)
    return;
  for (i = n_local_ipaddrs = 0;
       n_local_ipaddrs < MAX_LOCAL_IPADDRS &&
         ifn[i].if_name && *ifn[i].if_name;
       i++) {
    strcpy(ifr.ifr_name, ifn[i].if_name);
    if (ioctl(sk, SIOCGIFADDR, &ifr) || ifr.ifr_addr.sa_family != AF_INET)
      continue;
    local_ipaddrs[n_local_ipaddrs++] =
      SIN(&ifr.ifr_addr)->sin_addr;
    D( fprintf(stderr, "noip: local addr %s = %s\n", ifn[i].if_name,
	       inet_ntoa(local_ipaddrs[n_local_ipaddrs - 1])); )
  }
  close(sk);
}

static void setup(void)
{
  PRESERVING_ERRNO({
    char *p;

    import();
    uid = getuid();
    if ((p = getenv("NOIP_DEBUG")) && atoi(p))
      debug = 1;
    get_local_ipaddrs();
    readconfig();
    mkdir(sockdir, 0700);
    cleanup_sockdir();
  });
}