path: root/cprogs/cgi-fcgi-interp.c

/*
 * "Interpreter" that you can put in #! like this
 *   #!/usr/bin/cgi-fcgi-interp [<options>] <interpreter>
 *   #!/usr/bin/cgi-fcgi-interp [<options>],<interpreter>
 */
/*
 * cgi-fcgi-interp.[ch] - C helpers common to the whole of chiark-utils
 *
 * Copyright 2016 Ian Jackson
 * Copyright 1982,1986,1993 The Regents of the University of California
 *
 * 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 3 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 file; if not, consult the Free Software
 * Foundation's website at www.fsf.org, or the GNU Project website at
 * www.gnu.org.
 *
 * See below for a BSD 3-clause notice regarding timespeccmp.
 */
/*
 * The result is a program which looks, when executed via the #!
 * line, like a CGI program.  But the script inside will be executed
 * via <interpreter> in an fcgi context.
 *
 * Options:
 *
 *  <interpreter>
 *          The real interpreter to use.  Eg "perl".  Need not
 *          be an absolute path; will be fed to execvp.
 *
 *  -g<ident>
 *          Use <ident> rather than hex(sha256(<interp>\0<script>\0))
 *          as the basename of the leafname of the fcgi rendezvous
 *          socket.  If <ident> contains only hex digit characters it
 *          ought to be no more than 32 characters.  <ident> should
 *          not contain spaces or commas (see below).
 *
 *  -M<numservers>
 *         Start <numservers> instances of the program.  This
 *         determines the maximum concurrency.  (Note that unlike
 *         speedy, the specified number of servers is started
 *         right away.)  The default is 4.
 *
 *  -c<interval>
 *         Stale server check interval, in seconds.  The worker
 *         process group will get a SIGTERM when it is no longer
 *         needed to process new requests.  Ideally it would continue
 *         to serve any existing requests.  The SIGTERM will arrive no
 *         earlier than <interval> after the last request arrived at
 *         the containing webserver.  Default is 300.
 *
 *  -D
 *         Debug mode.  Do not actually run program.  Instead, print
 *         out what we would do.
 *
 * <options> and <interpreter> can be put into a single argument
 * to cgi-fcgi-interp, separated by spaces or commas.  <interpreter>
 * must come last.
 *
 * cgi-fcgi-interp automatically expires old sockets, including
 * ones where the named script is out of date.
 */
/*
 * Uses one of two directories
 *   /var/run/user/<UID>/cgi-fcgi-interp/
 *   ~/.cgi-fcgi-interp/<node>/
 * and inside there uses these paths
 *   s<ident>
 *   l<ident>    used to lock around garbage collection
 *
 * If -M<ident> is not specified then an initial substring of the
 * lowercase hex of the sha256 of <interp>\0<script>\0 is
 * used.  The substring is chosen so that the whole path is 10 bytes
 * shorter than sizeof(sun_path).  But always at least 33 characters.
 *
 * <node> is truncated at the first `.' and after the first 32
 * characters.
 *
 * Algorithm:
 *  - see if /var/run/user exists
 *       if so, lstat /var/run/user/<UID> and check that
 *         we own it and it's X700; if not, fail
 *         if it's ok then <base> is /var/run/user/<UID>
 *       otherwise, look for and maybe create ~/.cgi-fcgi-interp
 *         (where ~ is HOME or from getpwuid)
 *         and then <base> is ~/.cgi-fcgi-interp/<node>
 *  - calculate pathname (checking <ident> length is OK)
 *  - check for and maybe create <base>
 *  - stat and lstat the <script>
 *  - stat the socket and check its timestamp
 *       if it is too old, unlink it
 *  - dup stderr, mark no cloexec
 *  - set CHIARKUTILS_CGIFCGIINTERP_STAGE2=<stderr-copy-fd>
 *  - run     cgi-fcgi -connect SOCKET <script>
 *
 * When CHIARKUTILS_CGIFCGIINTERP_STAGE2 is set, --stage2 does this:
 *  - dup2 <was-stderr> to fd 2
 *  - open /dev/null and expect fd 1 (and if not, close it)
 *  - become a new process group
 *  - lstat <socket> to find its inum, mtime
 *  - fork/exec <interp> <script>
 *  - periodically lstat <interp> and <script> and
 *      if mtime is newer than our start time
 *      kill process group (at second iteration)
 */

#include "common.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <stdbool.h>
#include <assert.h>
#include <limits.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/utsname.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/file.h>
#include <unistd.h>
#include <fcntl.h>
#include <pwd.h>
#include <err.h>
#include <time.h>
#include <signal.h>
#include <sys/wait.h>
	
#include <nettle/sha.h>

#include "myopt.h"

#define die  common_die
#define diee common_diee

#define MINHEXHASH 33
#define STAGE2_VAR "CHIARKUTILS_CGIFCGIINTERP_STAGE2"

static const char *interp, *ident;
static int numservers=4, debugmode;
static int check_interval=300;

static struct sha256_ctx identsc;

const char *stage2;

void diee(const char *m) {
  err(127, "error: %s failed", m);
}

static void fusagemessage(FILE *f) {
  fprintf(f, "usage: #!/usr/bin/cgi-fcgi-interp [<options>]\n");
}

void usagemessage(void) { fusagemessage(stderr); }

static void of_help(const struct cmdinfo *ci, const char *val) {
  fusagemessage(stdout);
  if (ferror(stdout)) diee("write usage message to stdout");
  exit(0);
}

static void of_iassign(const struct cmdinfo *ci, const char *val) {
  long v;
  char *ep;
  errno= 0; v= strtol(val,&ep,10);
  if (!*val || *ep || errno || v<INT_MIN || v>INT_MAX)
    badusage("bad integer argument `%s' for --%s",val,ci->olong);
  *ci->iassignto = v;
}

static void ident_addstring(const struct cmdinfo *ci, const char *string) {
  /* ci may be 0 and is provided so this can be .call */
  sha256_update(&identsc,strlen(string)+1,string);
}

#define MAX_OPTS 5

static const struct cmdinfo cmdinfos[]= {
  { "help",   0, .call=of_help                                         },
  { 0, 'g',   1,                    .sassignto= &ident                 },
  { 0, 'M',   1, .call=of_iassign,  .iassignto= &numservers            },
  { 0, 'D',   0,                    .iassignto= &debugmode,    .arg= 1 },
  { 0, 'c',   1, .call=of_iassign,  .iassignto= &check_interval        },
  { 0 }
};

static uid_t us;
static const char *run_base, *script, *socket_path;
static const char *run_base_mkdir_p;
static int stderr_copy;

static bool find_run_base_var_run(void) {
  struct stat stab;
  char *try;
  int r;

  try = m_asprintf("%s/%lu", "/var/run/user", us);
  r = lstat(try, &stab);
  if (r<0) {
    if (errno == ENOENT ||
	errno == ENOTDIR ||
	errno == EACCES ||
	errno == EPERM)
      return 0; /* oh well */
    diee("stat /var/run/user/UID");
  }
  if (!S_ISDIR(stab.st_mode)) {
    warnx("%s not a directory, falling back to ~\n", try);
    return 0;
  }
  if (stab.st_uid != us) {
    warnx("%s not owned by uid %lu, falling back to ~\n", try,
	  (unsigned long)us);
    return 0;
  }
  if (stab.st_mode & 0077) {
    warnx("%s writeable by group or other, falling back to ~\n", try);
    return 0;
  }
  run_base = m_asprintf("%s/%s", try, "cgi-fcgi-interp");
  return 1;
}

static bool find_run_base_home(void) {
  struct passwd *pw;
  struct utsname ut;
  char *dot, *try;
  int r;

  pw = getpwuid(us);  if (!pw) diee("getpwent(uid)");

  r = uname(&ut);   if (r) diee("uname(2)");
  dot = strchr(ut.nodename, '.');
  if (dot) *dot = 0;
  if (sizeof(ut.nodename) > 32)
    ut.nodename[32] = 0;

  run_base_mkdir_p = m_asprintf("%s/%s", pw->pw_dir, ".cgi-fcgi-interp");
  try = m_asprintf("%/%s", run_base_mkdir_p, ut.nodename);
  run_base = try;
  return 1;
}

static void find_socket_path(void) {
  struct sockaddr_un sun;
  int r;

  us = getuid();  if (us==(uid_t)-1) diee("getuid");

  find_run_base_var_run() ||
    find_run_base_home() ||
    (abort(),0);

  int maxidentlen = sizeof(sun.sun_path) - strlen(run_base) - 10 - 2;

  if (!ident) {
    if (maxidentlen < MINHEXHASH)
      errx(127,"base directory `%s'"
	   " leaves only %d characters for id hash"
	   " which is too little (<%d)",
	   run_base, maxidentlen, MINHEXHASH);

    int identlen = maxidentlen > 64 ? 64 : maxidentlen;
    char *hexident = xmalloc(identlen + 2);
    unsigned char bbuf[32];
    int i;

    ident_addstring(0,interp);
    ident_addstring(0,script);
    sha256_digest(&identsc,sizeof(bbuf),bbuf);

    for (i=0; i<identlen; i += 2)
      sprintf(hexident+i, "%02x", bbuf[i/2]);

    hexident[identlen] = 0;
    ident = hexident;
  }

  if (strlen(ident) > maxidentlen)
    errx(127, "base directory `%s' plus ident `%s' too long"
	 " (with spare) for socket (max ident %d)\n",
	 run_base, ident, maxidentlen);

  r = mkdir(run_base, 0700);
  if (r && errno==ENOENT && run_base_mkdir_p) {
    r = mkdir(run_base_mkdir_p, 0700);
    if (r) err(127,"mkdir %s (since %s was ENOENT)",run_base_mkdir_p,run_base);
    r = mkdir(run_base, 0700);
  }
  if (r) {
    if (!(errno == EEXIST))
      err(127,"mkdir %s",run_base);
  }

  socket_path = m_asprintf("%s/s%s",run_base,ident);
}  

/*
 * Regarding the macro timespeccmp:
 *
 * Copyright (c) 1982, 1986, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)time.h      8.5 (Berkeley) 5/4/95
 * $FreeBSD: head/sys/sys/time.h 275985 2014-12-21 05:07:11Z imp $
 */
#ifndef timespeccmp
#define timespeccmp(tvp, uvp, cmp)                                      \
        (((tvp)->tv_sec == (uvp)->tv_sec) ?                             \
            ((tvp)->tv_nsec cmp (uvp)->tv_nsec) :                       \
            ((tvp)->tv_sec cmp (uvp)->tv_sec))
#endif /*timespeccmp*/



#ifdef st_mtime

static bool stab_isnewer(const struct stat *a, const struct stat *b) {
  if (debugmode)
    fprintf(stderr,"stab_isnewer mtim %lu.%06lu %lu.06%lu\n",
	    (unsigned long)a->st_mtim.tv_sec,
	    (unsigned long)a->st_mtim.tv_nsec,
	    (unsigned long)b->st_mtim.tv_sec,
	    (unsigned long)b->st_mtim.tv_nsec);
  return timespeccmp(&a->st_mtim, &b->st_mtim, >);
}

static void stab_mtimenow(struct stat *out) {
  int r = clock_gettime(CLOCK_REALTIME, &out->st_mtim);
  if (r) err(127,"(stage2) clock_gettime");
  if (debugmode)
    fprintf(stderr,"stab_mtimenow mtim %lu.%06lu\n",
	    (unsigned long)out->st_mtim.tv_sec,
	    (unsigned long)out->st_mtim.tv_nsec);
}

#else /* !defined(st_mtime) */

static bool stab_isnewer(const struct stat *a, const struct stat *b) {
  if (debugmode)
    fprintf(stderr,"stab_isnewer mtime %lu %lu\n",
	    (unsigned long)a->st_mtime,
	    (unsigned long)b->st_mtime);
  return a->st_mtime > &b->st_mtime;
}

static void stab_mtimenow(struct stat *out) {
  out->st_mtime = time(NULL);
  if (baseline_time.st_mtime == (time_t)-1) err(127,"(stage2) time()");
  if (debugmode)
    fprintf(stderr,"stab_mtimenow mtime %lu\n",
	    (unsigned long)out->st_mtime);
}

#endif /* !defined(st_mtime) */

static bool check_garbage_vs(const struct stat *started) {
  struct stat script_stab;
  int r;

  r = lstat(script, &script_stab);
  if (r) err(127,"lstat script (%s)",script);

  if (stab_isnewer(&script_stab, started))
    return 1;

  if (S_ISLNK(script_stab.st_mode)) {
    r = stat(script, &script_stab);
    if (r) err(127,"stat script (%s0",script);

    if (stab_isnewer(&script_stab, started))
      return 1;
  }

  return 0;
}

static bool check_garbage(void) {
  struct stat sock_stab;
  int r;

  r = lstat(socket_path, &sock_stab);
  if (r) {
    if ((errno == ENOENT))
      return 0; /* well, no garbage then */
    err(127,"stat socket (%s)",socket_path);
  }

  return check_garbage_vs(&sock_stab);
}

static void tidy_garbage(void) {
  /* We lock l<ident> and re-check.  The effect of this is that each
   * stale socket is removed only once.  So unless multiple updates to
   * the script happen rapidly, we can't be racing with the cgi-fcgi
   * (which is recreating the socket */
  int lockfd = -1;
  int r;

  const char *lock_path = m_asprintf("%s/l%s",run_base,ident);

  lockfd = open(lock_path, O_CREAT|O_RDWR, 0600);
  if (lockfd<0) err(127,"create lock (%s)", lock_path);

  r = flock(lockfd, LOCK_EX);
  if (r) err(127,"lock lock (%s)", lock_path);

  if (check_garbage()) {
    r = unlink(socket_path);
    if (r) {
      if (!(errno == ENOENT))
	err(127,"remove out-of-date socket (%s)", socket_path);
    }
  }

  r = close(lockfd);
  if (r) errx(127,"close lock (%s)", lock_path);
}

static void make_stderr_copy(void) {
  stderr_copy = dup(2);
  if (stderr_copy < 0) err(127,"dup stderr (for copy for stage2)");
}

static void prep_stage2(void) {
  int r;
  
  const char *stage2_val = m_asprintf("%d", stderr_copy);
  r = setenv(STAGE2_VAR, stage2_val, 1);
  if (r) err(127,"set %s (to announce to stage2)", STAGE2_VAR);
}

static void shbang_opts(const char *const **argv_io,
			const struct cmdinfo *cmdinfos) {
  myopt(argv_io, cmdinfos);

  interp = *(*argv_io)++;
  if (!interp) errx(127,"need interpreter argument");
}

/* stage2 predeclarations */
static void record_baseline_time(void);
static void become_pgrp(void);
static void setup_handlers(void);
static void spawn_script(void);
static void queue_alarm(void);
static void await_something(void);

int main(int argc, const char *const *argv) {
  const char *smashedopt;
  int r;

  stage2 = getenv(STAGE2_VAR);
  if (stage2) {
    int stderrfd = atoi(stage2);
    assert(stderrfd>2);

    r = dup2(stderrfd, 2);
    assert(r==2);

    r = open("/dev/null",O_WRONLY);
    if (r<0) err(127,"open /dev/null as stdout");
    if (r>=3) close(r);
    else if (r!=1) errx(127,"open /dev/null for stdout gave bad fd %d",r);
  }

  sha256_init(&identsc);

  if (argc>=2 &&
      (smashedopt = argv[1]) &&
      smashedopt[0]=='-' &&
      (strchr(smashedopt,' ') || strchr(smashedopt,','))) {
    /* single argument containg all the options and <interp> */
    argv += 2; /* eat argv[0] and smashedopt */
    const char *split_args[MAX_OPTS+1];
    int split_argc = 0;
    split_args[split_argc++] = argv[0];
    for (;;) {
      if (split_argc >= MAX_OPTS) errx(127,"too many options in combined arg");
      split_args[split_argc++] = smashedopt;
      if (smashedopt[0] != '-') /* never true on first iteration */
	break;
      char *delim = strchr(smashedopt,' ');
      if (!delim) delim = strchr(smashedopt,',');
      if (!delim)
	errx(127,"combined arg lacks <interpreter>");
      *delim = 0;
      smashedopt = delim+1;
    }
    assert(split_argc <= MAX_OPTS);
    split_args[split_argc++] = 0;

    const char *const *split_argv = split_args;

    shbang_opts(&split_argv, cmdinfos);
    /* sets interp */
    if (!split_argv) errx(127,"combined arg too many non-option arguments");
  } else {
    shbang_opts(&argv, cmdinfos);
  }

  script = *argv++;
  if (!script) errx(127,"need script argument");
  if (*argv) errx(127,"too many arguments");

  if (!stage2) {
    
    find_socket_path();

    bool isgarbage = check_garbage();

    if (debugmode) {
      printf("socket: %s\n",socket_path);
      printf("interp: %s\n",interp);
      printf("script: %s\n",script);
      printf("garbage: %d\n",isgarbage);
      exit(0);
    }

    if (isgarbage)
      tidy_garbage();

    make_stderr_copy();
    prep_stage2();

    execlp("cgi-fcgi",
	   "cgi-fcgi", "-connect", socket_path,
	   script,
	   m_asprintf("%d", numservers),
	   (char*)0);
    err(127,"exec cgi-fcgi");
    
  } else { /*stage2*/

    record_baseline_time();
    become_pgrp();
    setup_handlers();
    spawn_script();
    queue_alarm();
    await_something();
    abort();

  }
}

/* stage2 */

/* It is most convenient to handle the recheck timeout, as well as
 * child death, in signal handlers.  Our signals all block each other,
 * and the main program has signals blocked except in sigsuspend, so
 * we don't need to worry about async-signal-safety, or errno. */

static struct stat baseline_time;
static pid_t script_child, stage2_pgrp;
static bool out_of_date;

static void record_baseline_time(void) {
  stab_mtimenow(&baseline_time);
}

static void become_pgrp(void) {
  int r;

  stage2_pgrp = getpid();

  r = setpgid(0,0);
  if (r) err(127,"(stage2) setpgid");
}

static void atexit_handler(void) {
  int r;

  sighandler_t sigr = signal(SIGTERM,SIG_IGN);
  if (sigr == SIG_ERR) warn("(stage2) signal(SIGTERM,SIG_IGN)");

  r = killpg(stage2_pgrp,SIGTERM);
  if (r) warn("(stage) killpg failed");
}

static void alarm_handler(int dummy) {
  if (out_of_date)
    /* second timeout */
    exit(0); /* transfers control to atexit_handler */

  out_of_date = check_garbage_vs(&baseline_time);
  queue_alarm();
}

static void child_handler(int dummy) {
  for (;;) {
    int status;
    pid_t got = waitpid(-1, &status, WNOHANG);
    if (got == (pid_t)-1) err(127,"(stage2) waitpid");
    if (got != script_child) {
      warn("(stage2) waitpid got status %d for unknown child [%lu]",
	   status, (unsigned long)got);
      continue;
    }
    if (WIFEXITED(status)) {
      int v = WEXITSTATUS(status);
      if (v) warn("program failed with error exit status %d", v);
      exit(status);
    } else if (WIFSIGNALED(status)) {
      int s = WTERMSIG(status);
      err(status & 0xff, "program died due to fatal signal %s%s",
	  strsignal(s), WCOREDUMP(status) ? " (core dumped" : "");
    } else {
      err(127, "program failed with crazy wait status %#x", status);
    }
  }
  exit(127);
}

static void setup_handlers(void) {
  struct sigaction sa;
  int r;

  r = atexit(atexit_handler);
  if (r) err(127,"(stage2) atexit");

  sigemptyset(&sa.sa_mask);
  sigaddset(&sa.sa_mask, SIGALRM);
  sigaddset(&sa.sa_mask, SIGCHLD);
  sa.sa_flags = 0;

  r = sigprocmask(SIG_BLOCK, &sa.sa_mask, 0);
  if (r) err(127,"(stage2) sigprocmask(SIG_BLOCK,)");

  sa.sa_handler = alarm_handler;
  r = sigaction(SIGALRM, &sa, 0);
  if (r) err(127,"(stage2) sigaction SIGALRM");

  sa.sa_flags |= SA_NOCLDSTOP;
  sa.sa_handler = child_handler;
  r = sigaction(SIGCHLD, &sa, 0);
  if (r) err(127,"(stage2) sigaction SIGCHLD");
}

static void spawn_script(void) {
  script_child = fork();
  if (script_child == (pid_t)-1) err(127,"(stage2) fork");
  if (!script_child) {
    execlp(interp,
	   interp, script, (char*)0);
    err(127,"(stage2) exec interpreter (`%s', for `%s')\n",interp,script);
  }
}

static void queue_alarm(void) {
  alarm(check_interval);
}

static void await_something(void) {
  int r;
  sigset_t mask;
  sigemptyset(&mask);

  for (;;) {
    r = sigsuspend(&mask);
    assert(r==-1);
    if (errno != EINTR) err(127,"(stage2) sigsuspend");
  }
}