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[distorted-backup] / rfreezefs.c

/* -*-c-*-
 *
 * Freeze a file system under remote control
 *
 * (c) 2011 Mark Wooding
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>

#include <sys/types.h>
#include <sys/time.h>
#include <sys/select.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>

#include <linux/fs.h>

#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netdb.h>

#include <mLib/alloc.h>
#include <mLib/dstr.h>
#include <mLib/base64.h>
#include <mLib/fdflags.h>
#include <mLib/mdwopt.h>
#include <mLib/quis.h>
#include <mLib/report.h>
#include <mLib/sub.h>
#include <mLib/tv.h>

/*----- Magic constants ---------------------------------------------------*/

#define COOKIESZ 16			/* Size of authentication cookie */
#define TO_CONNECT 30			/* Timeout for incoming connection */
#define TO_KEEPALIVE 60			/* Timeout between keepalives */

/*----- Utility functions -------------------------------------------------*/

static int getuint(const char *p, const char *q)
{
  unsigned long i;
  int e = errno;
  char *qq;

  if (!q) q = p + strlen(p);
  errno = 0;
  i = strtoul(p, &qq, 0);
  if (errno || qq < q || i > INT_MAX)
    die(1, "invalid integer `%s'", p);
  errno = e;
  return ((int)i);
}

#ifdef DEBUG
#  define D(x) x
#else
#  define D(x)
#endif

/*----- Token management --------------------------------------------------*/

struct token {
  const char *label;
  char tok[(COOKIESZ + 2)*4/3 + 1];
};

#define TOKENS(_)							\
  _(FREEZE)								\
  _(FROZEN)								\
  _(KEEPALIVE)								\
  _(THAW)								\
  _(THAWED)

enum {
#define ENUM(tok) T_##tok,
  TOKENS(ENUM)
#undef ENUM
  T_LIMIT
};

enum {
#define MASK(tok) TF_##tok = 1u << T_##tok,
  TOKENS(MASK)
#undef ENUM
  TF_ALL = (1u << T_LIMIT) - 1u
};

static struct token toktab[] = {
#define INIT(tok) { #tok },
  TOKENS(INIT)
#undef INIT
  { 0 }
};

static void inittoks(void)
{
  static struct token *t, *tt;
  unsigned char buf[COOKIESZ];
  int fd;
  ssize_t n;
  base64_ctx bc;
  dstr d = DSTR_INIT;

  if ((fd = open("/dev/urandom", O_RDONLY)) < 0)
    die(2, "open (urandom): %s", strerror(errno));

  for (t = toktab; t->label; t++) {
  again:
    n = read(fd, buf, COOKIESZ);
    if (n < 0) die(2, "read (urandom): %s", strerror(errno));
    else if (n < COOKIESZ) die(2, "read (urandom): short read");
    base64_init(&bc);
    base64_encode(&bc, buf, COOKIESZ, &d);
    base64_encode(&bc, 0, 0, &d);
    dstr_putz(&d);

    for (tt = toktab; tt < t; tt++) {
      if (strcmp(d.buf, tt->tok) == 0)
	goto again;
    }

    assert(d.len < sizeof(t->tok));
    memcpy(t->tok, d.buf, d.len + 1);
    dstr_reset(&d);
  }
}

struct tokmatch {
  unsigned tf;				/* Possible token matches */
  size_t o;				/* Offset into token string */
  unsigned f;				/* Flags */
#define TMF_CR 1u			/*   Seen trailing carriage-return */
};

static void tokmatch_init(struct tokmatch *tm)
  { tm->tf = TF_ALL; tm->o = 0; tm->f = 0; }

static int tokmatch_update(struct tokmatch *tm, int ch)
{
  const struct token *t;
  unsigned tf;

  switch (ch) {
    case '\n':
      for (t = toktab, tf = 1; t->label; t++, tf <<= 1) {
	if ((tm->tf & tf) && !t->tok[tm->o])
	  return (tf);
      }
      return (-1);
    case '\r':
      for (t = toktab, tf = 1; t->label; t++, tf <<= 1) {
	if ((tm->tf & tf) && !t->tok[tm->o] && !(tm->f & TMF_CR))
	  tm->f |= TMF_CR;
	else
	  tm->tf &= ~tf;
      }
      break;
    default:
      for (t = toktab, tf = 1; t->label; t++, tf <<= 1) {
	if ((tm->tf & tf) && ch != t->tok[tm->o])
	  tm->tf &= ~tf;
      }
      tm->o++;
      break;
  }
  return (0);
}

static int writetok(unsigned i, int fd)
{
  static const char nl = '\n';
  const struct token *t = &toktab[i];
  size_t n = strlen(t->tok);

  errno = EIO;
  if (write(fd, t->tok, n) < n ||
      write(fd, &nl, 1) < 1)
    return (-1);
  return (0);
}

/*----- Data structures ---------------------------------------------------*/

struct client {
  struct client *next;			/* Links in the client chain */
  int fd;				/* File descriptor for socket */
  struct tokmatch tm;			/* Token matching context */
};

/*----- Static variables --------------------------------------------------*/

static int *fs;				/* File descriptors for targets */
static char **fsname;			/* File system names */
static size_t nfs;			/* Number of descriptors */

/*----- Cleanup -----------------------------------------------------------*/

#define EOM ((char *)0)
static void emerg(const char *msg,...)
{
  va_list ap;

#define MSG(m)								\
  do { const char *m_ = m; if (write(2, m_, strlen(m_))); } while (0)

  va_start(ap, msg);
  MSG(QUIS); MSG(": ");
  do {
    MSG(msg);
    msg = va_arg(ap, const char *);
  } while (msg != EOM);
  MSG("\n");

#undef MSG
}

static void partial_cleanup(size_t n)
{
  int i;
  int bad = 0;

  for (i = 0; i < nfs; i++) {
    if (fs[i] == -1)
      emerg("not really thawing ", fsname[i], EOM);
    else if (fs[i] != -2) {
      if (ioctl(fs[i], FITHAW, 0)) {
	emerg("VERY BAD!  failed to thaw ",
	      fsname[i], ": ", strerror(errno), EOM);
	bad = 1;
      }
      close(fs[i]);
    }
    fs[i] = -2;
  }
  if (bad) _exit(112);
}

static void cleanup(void) { partial_cleanup(nfs); }

static int sigcatch[] = {
  SIGINT, SIGQUIT, SIGTERM, SIGHUP, SIGALRM,
  SIGILL, SIGSEGV, SIGBUS, SIGFPE, SIGABRT
};

static void sigmumble(int sig)
{
  sigset_t ss;

  cleanup();
  emerg(strsignal(sig), 0);

  signal(sig, SIG_DFL);
  sigemptyset(&ss); sigaddset(&ss, sig);
  sigprocmask(SIG_UNBLOCK, &ss, 0);
  raise(sig);
  _exit(4);
}

/*----- Help functions ----------------------------------------------------*/

static void version(FILE *fp) { pquis(fp, "$, version " VERSION "\n"); }
static void usage(FILE *fp)
  { pquis(fp, "Usage: $ [-n] [-a ADDR] [-p LOPORT[-HIPORT]] FILSYS ...\n"); }

static void help(FILE *fp)
{
  version(fp); putc('\n', fp);
  usage(fp);
  fputs("\n\
Freezes a filesystem temporarily, with some measure of safety.\n\
\n\
The program listens for connections on a TCP port, and prints a line\n\
\n\
	PORT COOKIE\n\
\n\
to standard output.  You must connect to this PORT and send the COOKIE\n\
followed by a newline within a short period of time.  The filesystems\n\
will then be frozen, and `OK' written to the connection.  In order to\n\
keep the file system frozen, you must keep the connection open, and\n\
feed data into it.  If the connection closes, or no data is received\n\
within a set period of time, or the program receives one of a variety\n\
of signals or otherwise becomes unhappy, the filesystems are thawed again.\n\
\n\
Options:\n\
\n\
-h, --help			Print this help text.\n\
-v, --version			Print the program version number.\n\
-u, --usage			Print a short usage message.\n\
\n\
-a, --address=ADDR		Listen only on ADDR.\n\
-n, --not-really		Don't really freeze or thaw filesystems.\n\
-p, --port-range=LO[-HI]	Select a port number between LO and HI.\n\
				  If HI is omitted, choose only LO.\n\
", fp);
}

/*----- Main program ------------------------------------------------------*/

int main(int argc, char *argv[])
{
  char buf[256];
  int loport = -1, hiport = -1;
  int sk, fd, maxfd;
  struct sockaddr_in sin;
  socklen_t sasz;
  struct hostent *h;
  const char *p, *q;
  struct timeval now, when, delta;
  struct client *clients = 0, *c, **cc;
  const struct token *t;
  struct tokmatch tm;
  fd_set fdin;
  int i;
  ssize_t n;
  unsigned f = 0;
#define f_bogus 0x01u
#define f_notreally 0x02u

  ego(argv[0]);
  sub_init();

  /* --- Partially initialize the socket address --- */

  sin.sin_family = AF_INET;
  sin.sin_addr.s_addr = INADDR_ANY;
  sin.sin_port = 0;

  /* --- Parse the command line --- */

  for (;;) {
    static struct option opts[] = {
      { "help",		0,		0,	'h' },
      { "version",	0,		0,	'v' },
      { "usage",	0,		0,	'u' },
      { "address",	OPTF_ARGREQ,	0,	'a' },
      { "not-really",	0,		0,	'n' },
      { "port-range",	OPTF_ARGREQ,	0,	'p' },
      { 0,		0,		0,	0 }
    };

    if ((i = mdwopt(argc, argv, "hvua:np:", opts, 0, 0, 0)) < 0) break;
    switch (i) {
      case 'h': help(stdout); exit(0);
      case 'v': version(stdout); exit(0);
      case 'u': usage(stdout); exit(0);
      case 'a':
	if ((h = gethostbyname(optarg)) == 0) {
	  die(1, "failed to resolve address `%s': %s",
	      optarg, hstrerror(h_errno));
	}
	if (h->h_addrtype != AF_INET)
	  die(1, "unexpected address type resolving `%s'", optarg);
	assert(h->h_length == sizeof(sin.sin_addr));
	memcpy(&sin.sin_addr, h->h_addr, sizeof(sin.sin_addr));
	break;
      case 'n': f |= f_notreally; break;
      case 'p':
	if ((p = strchr(optarg, '-')) == 0)
	  loport = hiport = getuint(optarg, 0);
	else {
	  loport = getuint(optarg, p);
	  hiport = getuint(p + 1, 0);
	}
	break;
      default: f |= f_bogus; break;
    }
  }
  if (f & f_bogus) { usage(stderr); exit(1); }
  if (optind >= argc) { usage(stderr); exit(1); }

  /* --- Open the file systems --- */

  nfs = argc - optind;
  fsname = &argv[optind];
  fs = xmalloc(nfs*sizeof(*fs));
  for (i = 0; i < nfs; i++) {
    if ((fs[i] = open(fsname[i], O_RDONLY)) < 0)
      die(2, "open (%s): %s", fsname[i], strerror(errno));
  }

  if (f & f_notreally) {
    for (i = 0; i < nfs; i++) {
      close(fs[i]);
      fs[i] = -1;
    }
  }

  /* --- Generate random tokens --- */

  inittoks();

  /* --- Create the listening socket --- */

  if ((sk = socket(PF_INET, SOCK_STREAM, 0)) < 0)
    die(2, "socket: %s", strerror(errno));
  i = 1;
  if (setsockopt(sk, SOL_SOCKET, SO_REUSEADDR, &i, sizeof(i)))
    die(2, "setsockopt (reuseaddr): %s", strerror(errno));
  if (fdflags(sk, O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC))
    die(2, "fdflags: %s", strerror(errno));
  if (loport < 0 || loport == hiport) {
    if (loport >= 0) sin.sin_port = htons(loport);
    if (bind(sk, (struct sockaddr *)&sin, sizeof(sin)))
      die(2, "bind: %s", strerror(errno));
  } else if (hiport != loport) {
    for (i = loport; i <= hiport; i++) {
      sin.sin_port = htons(i);
      if (bind(sk, (struct sockaddr *)&sin, sizeof(sin)) >= 0) break;
      else if (errno != EADDRINUSE)
	die(2, "bind: %s", strerror(errno));
    }
    if (i > hiport) die(2, "bind: all ports in use");
  }
  if (listen(sk, 5)) die(2, "listen: %s", strerror(errno));

  /* --- Tell the caller how to connect to us, and start the timer --- */

  sasz = sizeof(sin);
  if (getsockname(sk, (struct sockaddr *)&sin, &sasz))
    die(2, "getsockname (listen): %s", strerror(errno));
  printf("PORT %d\n", ntohs(sin.sin_port));
  for (t = toktab; t->label; t++)
    printf("TOKEN %s %s\n", t->label, t->tok);
  printf("READY\n");
  if (fflush(stdout) || ferror(stdout))
    die(2, "write (stdout, rubric): %s", strerror(errno));
  gettimeofday(&now, 0); TV_ADDL(&when, &now, TO_CONNECT, 0);

  /* --- Collect incoming connections, and check for the cookie --- *
   *
   * This is the tricky part.
   */

  for (;;) {
    FD_ZERO(&fdin);
    FD_SET(sk, &fdin);
    maxfd = sk;
    for (c = clients; c; c = c->next) {
      FD_SET(c->fd, &fdin);
      if (c->fd > maxfd) maxfd = c->fd;
    }
    TV_SUB(&delta, &when, &now);
    if (select(maxfd + 1, &fdin, 0, 0, &delta) < 0)
      die(2, "select (accept): %s", strerror(errno));
    gettimeofday(&now, 0);

    if (TV_CMP(&now, >=, &when)) die(3, "timeout (accept)");

    if (FD_ISSET(sk, &fdin)) {
      sasz = sizeof(sin);
      fd = accept(sk, (struct sockaddr *)&sin, &sasz);
      if (fd >= 0) {
	if (fdflags(fd, O_NONBLOCK, O_NONBLOCK, FD_CLOEXEC, FD_CLOEXEC) < 0)
	  die(2, "fdflags: %s", strerror(errno));
	c = CREATE(struct client);
	c->next = clients; c->fd = fd; tokmatch_init(&c->tm);
	clients = c;
      }
#ifdef DEBUG
      else if (errno != EAGAIN)
	moan("accept: %s", strerror(errno));
#endif
    }

    for (cc = &clients; *cc;) {
      c = *cc;
      if (!FD_ISSET(c->fd, &fdin)) goto next_client;
      n = read(c->fd, buf, sizeof(buf));
      if (!n) goto disconn;
      else if (n < 0) {
	if (errno == EAGAIN) goto next_client;
	D( moan("read (client; auth): %s", strerror(errno)); )
	goto disconn;
      } else {
	for (p = buf, q = p + n; p < q; p++) {
	  switch (tokmatch_update(&c->tm, *p)) {
	    case 0: break;
	    case TF_FREEZE: goto connected;
	    default:
	      D( moan("bad token from client"); )
	      goto disconn;
	  }
	}
      }

    next_client:
      cc = &c->next;
      continue;

    disconn:
      close(c->fd);
      *cc = c->next;
      DESTROY(c);
      continue;
    }
  }

connected:
  close(sk); sk = fd;
  while (clients) {
    if (clients->fd != sk) close(clients->fd);
    c = clients->next;
    DESTROY(clients);
    clients = c;
  }

  /* --- Establish signal handlers --- *
   *
   * Hopefully this will prevent bad things happening if we have an accident.
   */

  for (i = 0; i < sizeof(sigcatch)/sizeof(sigcatch[0]); i++) {
    if (signal(sigcatch[i], sigmumble) == SIG_ERR)
      die(2, "signal (%d): %s", i, strerror(errno));
  }
  atexit(cleanup);

  /* --- Prevent the OOM killer from clobbering us --- */

  if ((fd = open("/proc/self/oom_adj", O_WRONLY)) < 0 ||
      write(fd, "-17\n", 4) < 4 ||
      close(fd))
    die(2, "set oom_adj: %s", strerror(errno));

  /* --- Actually freeze the filesystem --- */

  for (i = 0; i < nfs; i++) {
    if (fs[i] == -1)
      moan("not really freezing %s", fsname[i]);
    else {
      if (ioctl(fs[i], FIFREEZE, 0) < 0) {
	partial_cleanup(i);
	die(2, "ioctl (freeze %s): %s", fsname[i], strerror(errno));
      }
    }
  }
  if (writetok(T_FROZEN, sk)) {
    cleanup();
    die(2, "write (frozen): %s", strerror(errno));
  }

  /* --- Now wait for the other end to detach --- */

  tokmatch_init(&tm);
  TV_ADDL(&when, &now, TO_KEEPALIVE, 0);
  for (p++; p < q; p++) {
    switch (tokmatch_update(&tm, *p)) {
      case 0: break;
      case TF_KEEPALIVE: tokmatch_init(&tm); break;
      case TF_THAW: goto done;
      default: cleanup(); die(3, "unknown token (keepalive)");
    }
  }
  for (;;) {
    FD_ZERO(&fdin);
    FD_SET(sk, &fdin);
    TV_SUB(&delta, &when, &now);
    if (select(sk + 1, &fdin, 0, 0, &delta) < 0) {
      cleanup();
      die(2, "select (keepalive): %s", strerror(errno));
    }

    gettimeofday(&now, 0);
    if (TV_CMP(&now, >, &when)) {
      cleanup(); die(3, "timeout (keepalive)");
    }
    if (FD_ISSET(sk, &fdin)) {
      n = read(sk, buf, sizeof(buf));
      if (!n) { cleanup(); die(3, "end-of-file (keepalive)"); }
      else if (n < 0) {
	if (errno == EAGAIN) ;
	else {
	  cleanup();
	  die(2, "read (client, keepalive): %s", strerror(errno));
	}
      } else {
	for (p = buf, q = p + n; p < q; p++) {
	  switch (tokmatch_update(&tm, *p)) {
	    case 0: break;
	    case TF_KEEPALIVE:
	      TV_ADDL(&when, &now, TO_KEEPALIVE, 0);
	      tokmatch_init(&tm);
	      break;
	    case TF_THAW:
	      goto done;
	    default:
	      cleanup();
	      die(3, "unknown token (keepalive)");
	  }
	}
      }
    }
  }

done:
  cleanup();
  if (writetok(T_THAWED, sk))
    die(2, "write (thaw): %s", strerror(errno));
  close(sk);
  return (0);
}

/*----- That's all, folks -------------------------------------------------*/