spawn-process-helper.c

   1 /**
   2  * (C) Copyright 2008 Jeremy Maitin-Shepard
   3  *
   4  * Use, modification, and distribution are subject to the terms specified in the
   5  * COPYING file.
   6  **/
   7
   8 #include <sys/types.h>
   9 #include <sys/socket.h>
  10 #include <unistd.h>
  11 #include <stdio.h>
  12 #include <errno.h>
  13 #include <stdlib.h>
  14 #include <signal.h>
  15 #include <sys/wait.h>
  16 #include <sys/stat.h>
  17 #include <string.h>
  18 #include <fcntl.h>
  19 #include <netinet/in.h>
  20
  21 void fail(const char *msg) {
  22   fprintf(stderr, "%s\n", msg);
  23   exit(1);
  24 }
  25
  26 void failerr(const char *msg) {
  27   perror(msg);
  28   exit(1);
  29 }
  30
  31 #define TRY(var, foo) var = foo; while (var == -1) { if(errno != EINTR) failerr(#foo); }
  32
  33 void *Malloc(size_t count) { void *r = malloc(count); if (!r) fail("malloc"); return r; }
  34
  35 /**
  36  * read_all: read from the specified file descriptor, returning a
  37  * malloc-allocated buffer containing the data that was read; the
  38  * number of bytes read is stored in *bytes_read.  If max_bytes is
  39  * non-negative, it specifies the maximum number of bytes to read.
  40  * Otherwise, read_all reads from the file descriptor until the end of
  41  * file is reached.
  42  */
  43 char *read_all(int fd, int max_bytes, int *bytes_read) {
  44   int capacity = 256;
  45   if (max_bytes > 0)
  46     capacity = max_bytes;
  47   char *buffer = Malloc(capacity);
  48   int count = 0;
  49   if (max_bytes < 0 || max_bytes > 0) {
  50     while (1) {
  51       int remain;
  52       if (count == capacity) {
  53         capacity *= 2;
  54         buffer = realloc(buffer, capacity);
  55         if (!buffer)
  56           fail("realloc failed");
  57       }
  58       remain = capacity - count;
  59       if (max_bytes > 0 && remain > max_bytes)
  60         remain = max_bytes;
  61       TRY(remain, read(fd, buffer + count, remain));
  62       count += remain;
  63       if (remain == 0 || count == max_bytes)
  64         break;
  65     }
  66   }
  67   *bytes_read = count;
  68   return buffer;
  69 }
  70
  71 /**
  72  * next_term: return the next NUL terminated string from buffer, and
  73  * adjust buffer and len accordingly.
  74  */
  75 char *next_term(char **buffer, int *len) {
  76   char *p = *buffer;
  77   int x = strnlen(p, *len);
  78   if (x == *len)
  79     fail("error parsing");
  80   *buffer += x + 1;
  81   *len -= (x + 1);
  82   return p;
  83 }
  84
  85 struct fd_info {
  86   int desired_fd;
  87   int orig_fd;
  88   char *path;
  89   int open_mode;
  90   int perms;
  91 };
  92
  93 void write_all(int fd, const char *buf, int len) {
  94   int result;
  95   do {
  96     TRY(result, write(fd, buf, len));
  97     buf += result;
  98     len -= result;
  99   } while (len > 0);
 100 }
 101
 102 /**
 103  * my_connect: Create a connection to the local Conkeror process on
 104  * the specified TCP port.  After connecting, the properly formatted
 105  * header specifying the client_key and the "role" (file descriptor or
 106  * -1 to indicate the control socket) are sent as well.  The file
 107  * descriptor for the socket is returned.
 108  */
 109 int my_connect(int port, char *client_key, int role) {
 110   int sockfd;
 111   int result;
 112   struct sockaddr_in sa;
 113
 114   TRY(sockfd, socket(PF_INET, SOCK_STREAM, 0));
 115   sa.sin_family = AF_INET;
 116   sa.sin_port = htons(port);
 117   sa.sin_addr.s_addr = inet_addr("127.0.0.1");
 118   memset(sa.sin_zero, 0, sizeof(sa.sin_zero));
 119
 120   TRY(result, connect(sockfd, (struct sockaddr *)&sa, sizeof(sa)));
 121
 122   /* Send the client key */
 123   write_all(sockfd, client_key, strlen(client_key));
 124
 125   /* Send the role */
 126   if (role < 0) {
 127     write_all(sockfd, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 15);
 128   }
 129   else {
 130     char buf[16];
 131     snprintf(buf, 16, "%15d", role);
 132     write_all(sockfd, buf, 15);
 133   }
 134
 135   return sockfd;
 136 }
 137
 138 int child_pid = 0;
 139 int control_fd;
 140
 141 /**
 142  * sigchld_handler: reap any waitable children.  Once the child
 143  * process exits, send the exit status back over the control socket,
 144  * then exit. */
 145 void sigchld_handler(int sig) {
 146   int status;
 147   int pid;
 148   int err;
 149
 150   while (1) {
 151     pid = waitpid(-1, &status, WNOHANG);
 152     if (pid == 0)
 153       return;
 154     if (pid == -1) {
 155       if (errno == ECHILD)
 156         break;
 157       failerr("waitpid");
 158     }
 159
 160     /* Our child process exited */
 161     if (pid == child_pid && (WIFEXITED(status) || WIFSIGNALED(status))) {
 162       char buf[30];
 163       snprintf(buf, 30, "%d", status);
 164       write_all(control_fd, buf, strlen(buf) + 1);
 165       exit(0);
 166     }
 167   }
 168 }
 169
 170 void check_duplicate_fds(struct fd_info *fds, int fd_count) {
 171   int i, j;
 172   for (i = 0; i < fd_count; ++i) {
 173     for (j = i + 1; j < fd_count; ++j) {
 174       if (fds[i].desired_fd == fds[j].desired_fd)
 175         fail("duplicate redirection requested");
 176     }
 177   }
 178 }
 179
 180 /**
 181  * setup_fds: Make the requested redirections.  For each entry in the
 182  * fds array, rename orig_fd to desired_fd.
 183  */
 184 void setup_fds(struct fd_info *fds, int fd_count) {
 185   int i, j, result;
 186   for (i = 0; i < fd_count; ++i) {
 187     int fd = fds[i].desired_fd;
 188     /* Check if this file descriptor is still in use by any subsequent
 189        redirection. */
 190     for (j = i + 1; j < fd_count; ++j) {
 191       if (fd == fds[j].orig_fd) {
 192         /* It is in use.  Pick a new file descriptor for fds[j]. */
 193         int fd_new;
 194         TRY(fd_new, dup(fds[j].orig_fd));
 195         close(fds[j].orig_fd);
 196         fds[j].orig_fd = fd_new;
 197         break;
 198       }
 199     }
 200     TRY(result, dup2(fd, fds[i].orig_fd));
 201     close(fds[i].orig_fd);
 202   }
 203 }
 204
 205 int main(int argc, char **argv) {
 206
 207   int port;
 208   char *client_key, *server_key, *executable, *workdir;
 209   char **my_argv;
 210   struct fd_info *fds;
 211   int fd_count;
 212   int i;
 213   sigset_t my_mask, my_old_mask;
 214
 215   if (argc != 3 || (port = atoi(argv[2])) == 0)
 216     fail("Invalid arguments");
 217
 218   sigemptyset(&my_mask);
 219   sigaddset(&my_mask, SIGCHLD);
 220
 221   /* Block SIGPIPE to avoid a signal being generated while writing to a socket */
 222   signal(SIGPIPE, SIG_IGN);
 223
 224   /* Parse key file */
 225   {
 226     char *buf;
 227     int len;
 228     int my_argc;
 229     /* Read the entire file into buf. */
 230     {
 231       int file;
 232       TRY(file, open(argv[1], O_RDONLY));
 233       buf = read_all(file, -1, &len);
 234       close(file);
 235
 236       /* Remove the temporary file */
 237       remove(argv[1]);
 238     }
 239     client_key = next_term(&buf, &len);
 240     server_key = next_term(&buf, &len);
 241     executable = next_term(&buf, &len);
 242     workdir = next_term(&buf, &len);
 243     my_argc = atoi(next_term(&buf, &len));
 244     my_argv = Malloc(sizeof(char *) * (my_argc + 1));
 245     for (i = 0; i < my_argc; ++i)
 246       my_argv[i] = next_term(&buf, &len);
 247     my_argv[my_argc] = NULL;
 248     fd_count = atoi(next_term(&buf, &len));
 249     if (fd_count < 0) fail("invalid fd count");
 250     fds = Malloc(sizeof(struct fd_info) * fd_count);
 251     for (i = 0; i < fd_count; ++i) {
 252       fds[i].desired_fd = atoi(next_term(&buf, &len));
 253       fds[i].path = next_term(&buf, &len);
 254       if (fds[i].path) {
 255         fds[i].open_mode = atoi(next_term(&buf, &len));
 256         fds[i].perms = atoi(next_term(&buf, &len));
 257       }
 258     }
 259     if (len != 0)
 260       fail("invalid input file");
 261   }
 262
 263   /* Validate the file descriptor redirection request. */
 264   check_duplicate_fds(fds, fd_count);
 265
 266   /* Create the control socket connection. */
 267   control_fd = my_connect(port, client_key, -1);
 268
 269   /* Create a socket connection or open a local file for each
 270      requested file descriptor redirection. */
 271   for (i = 0; i < fd_count; ++i) {
 272     if (fds[i].path) {
 273       TRY(fds[i].orig_fd, open(fds[i].path, fds[i].open_mode, fds[i].perms));
 274     } else {
 275       fds[i].orig_fd = my_connect(port, client_key, fds[i].desired_fd);
 276     }
 277   }
 278
 279   /* Check server key */
 280   {
 281     int len = strlen(server_key);
 282     int read_len;
 283     char *buf = read_all(control_fd, len, &read_len);
 284     if (len != read_len || memcmp(buf, server_key, len) != 0)
 285       fail("server key mismatch");
 286     free(buf);
 287   }
 288
 289   /* Block SIGCHLD */
 290   sigprocmask(SIG_BLOCK, &my_mask, &my_old_mask);
 291
 292   /* Create the child process */
 293   child_pid = fork();
 294   if (child_pid == 0) {
 295     int result;
 296     /* Unblock SIGCHLD */
 297     sigprocmask(SIG_SETMASK, &my_old_mask, NULL);
 298
 299     /* Reset the SIGPIPE signal handler. */
 300     signal(SIGPIPE, SIG_DFL);
 301
 302     /* Close the control socket, as it isn't needed from the child. */
 303     close(control_fd);
 304
 305     /* Change to the specified working directory. */
 306     if (workdir[0] != 0) {
 307       if (chdir(workdir) == -1)
 308         failerr(workdir);
 309     }
 310
 311     /* Rearrange file descriptors according to the user specification */
 312     setup_fds(fds, fd_count);
 313
 314     /* Exec */
 315     TRY(result, execv(executable, my_argv));
 316
 317   } else if (child_pid == -1) {
 318     failerr("fork");
 319   } else {
 320     /* We are in the parent process */
 321     char msg;
 322     int count;
 323
 324     /* Install SIGCHLD handler */
 325     {
 326       struct sigaction act;
 327       act.sa_handler = sigchld_handler;
 328       sigemptyset(&act.sa_mask);
 329       act.sa_flags = SA_NOCLDSTOP;
 330       sigaction(SIGCHLD, &act, NULL);
 331     }
 332     /* Unblock SIGCHLD */
 333     sigprocmask(SIG_SETMASK, &my_old_mask, NULL);
 334
 335     /* Close all of the redirection file descriptors, as we don't need
 336        them from the parent. */
 337     for (i = 0; i < fd_count; ++i)
 338       close(fds[i].orig_fd);
 339
 340     /* Wait for a message from the server telling us to exit early. */
 341     TRY(count, read(control_fd, &msg, 1));
 342
 343     if (count == 0) {
 344       /* End of file received: exit without killing child */
 345       return;
 346     }
 347
 348     /* Assume msg == 0 until we support more messages */
 349     TRY(count, kill(child_pid, SIGTERM));
 350     return;
 351   }
 352 }