libio/iopopen.c

   1 /* Copyright (C) 1993-2019 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Written by Per Bothner <bothner@cygnus.com>.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.
  18
  19    As a special exception, if you link the code in this file with
  20    files compiled with a GNU compiler to produce an executable,
  21    that does not cause the resulting executable to be covered by
  22    the GNU Lesser General Public License.  This exception does not
  23    however invalidate any other reasons why the executable file
  24    might be covered by the GNU Lesser General Public License.
  25    This exception applies to code released by its copyright holders
  26    in files containing the exception.  */
  27
  28 #include "libioP.h"
  29 #include <fcntl.h>
  30 #include <signal.h>
  31 #include <unistd.h>
  32 #include <stdlib.h>
  33 #include <shlib-compat.h>
  34 #include <not-cancel.h>
  35 #include <sys/types.h>
  36 #include <sys/wait.h>
  37 #include <spawn.h>
  38 #include <paths.h>
  39
  40 struct _IO_proc_file
  41 {
  42   struct _IO_FILE_plus file;
  43   /* Following fields must match those in class procbuf (procbuf.h) */
  44   pid_t pid;
  45   struct _IO_proc_file *next;
  46 };
  47 typedef struct _IO_proc_file _IO_proc_file;
  48
  49 static const struct _IO_jump_t _IO_proc_jumps;
  50
  51 static struct _IO_proc_file *proc_file_chain;
  52
  53 #ifdef _IO_MTSAFE_IO
  54 static _IO_lock_t proc_file_chain_lock = _IO_lock_initializer;
  55
  56 static void
  57 unlock (void *not_used)
  58 {
  59   _IO_lock_unlock (proc_file_chain_lock);
  60 }
  61 #endif
  62
  63 /* POSIX states popen shall ensure that any streams from previous popen()
  64    calls that remain open in the parent process should be closed in the new
  65    child process.
  66    To avoid a race-condition between checking which file descriptors need to
  67    be close (by transversing the proc_file_chain list) and the insertion of a
  68    new one after a successful posix_spawn this function should be called
  69    with proc_file_chain_lock acquired.  */
  70 static bool
  71 spawn_process (posix_spawn_file_actions_t *fa, FILE *fp, const char *command,
  72                int do_cloexec, int pipe_fds[2], int parent_end, int child_end,
  73                int child_pipe_fd)
  74 {
  75
  76   for (struct _IO_proc_file *p = proc_file_chain; p; p = p->next)
  77     {
  78       int fd = _IO_fileno ((FILE *) p);
  79
  80       /* If any stream from previous popen() calls has fileno
  81          child_pipe_fd, it has been already closed by the adddup2 action
  82          above.  */
  83       if (fd != child_pipe_fd
  84           && __posix_spawn_file_actions_addclose (fa, fd) != 0)
  85         return false;
  86     }
  87
  88   if (__posix_spawn (&((_IO_proc_file *) fp)->pid, _PATH_BSHELL, fa, 0,
  89                      (char *const[]){ (char*) "sh", (char*) "-c",
  90                      (char *) command, NULL }, __environ) != 0)
  91     return false;
  92
  93   __close_nocancel (pipe_fds[child_end]);
  94
  95   if (!do_cloexec)
  96     /* Undo the effects of the pipe2 call which set the
  97        close-on-exec flag.  */
  98     __fcntl (pipe_fds[parent_end], F_SETFD, 0);
  99
 100   _IO_fileno (fp) = pipe_fds[parent_end];
 101
 102   ((_IO_proc_file *) fp)->next = proc_file_chain;
 103   proc_file_chain = (_IO_proc_file *) fp;
 104
 105   return true;
 106 }
 107
 108 FILE *
 109 _IO_new_proc_open (FILE *fp, const char *command, const char *mode)
 110 {
 111   int read_or_write;
 112   /* These are indexes for pipe_fds.  */
 113   int parent_end, child_end;
 114   int pipe_fds[2];
 115   int child_pipe_fd;
 116   bool spawn_ok;
 117
 118   int do_read = 0;
 119   int do_write = 0;
 120   int do_cloexec = 0;
 121   while (*mode != '\0')
 122     switch (*mode++)
 123       {
 124       case 'r':
 125         do_read = 1;
 126         break;
 127       case 'w':
 128         do_write = 1;
 129         break;
 130       case 'e':
 131         do_cloexec = 1;
 132         break;
 133       default:
 134       errout:
 135         __set_errno (EINVAL);
 136         return NULL;
 137       }
 138
 139   if ((do_read ^ do_write) == 0)
 140     goto errout;
 141
 142   if (_IO_file_is_open (fp))
 143     return NULL;
 144
 145   /* Atomically set the O_CLOEXEC flag for the pipe end used by the
 146      child process (to avoid leaking the file descriptor in case of a
 147      concurrent fork).  This is later reverted in the child process.
 148      When popen returns, the parent pipe end can be O_CLOEXEC or not,
 149      depending on the 'e' open mode, but there is only one flag which
 150      controls both descriptors.  The parent end is adjusted below,
 151      after creating the child process.  (In the child process, the
 152      parent end should be closed on execve, so O_CLOEXEC remains set
 153      there.)  */
 154   if (__pipe2 (pipe_fds, O_CLOEXEC) < 0)
 155     return NULL;
 156
 157   if (do_read)
 158     {
 159       parent_end = 0;
 160       child_end = 1;
 161       read_or_write = _IO_NO_WRITES;
 162       child_pipe_fd = 1;
 163     }
 164   else
 165     {
 166       parent_end = 1;
 167       child_end = 0;
 168       read_or_write = _IO_NO_READS;
 169       child_pipe_fd = 0;
 170     }
 171
 172   posix_spawn_file_actions_t fa;
 173   /* posix_spawn_file_actions_init does not fail.  */
 174   __posix_spawn_file_actions_init (&fa);
 175
 176   /* The descriptor is already the one the child will use.  In this case
 177      it must be moved to another one otherwise, there is no safe way to
 178      remove the close-on-exec flag in the child without creating a FD leak
 179      race in the parent.  */
 180   if (pipe_fds[child_end] == child_pipe_fd)
 181     {
 182       int tmp = __fcntl (child_pipe_fd, F_DUPFD_CLOEXEC, 0);
 183       if (tmp < 0)
 184         goto spawn_failure;
 185       __close_nocancel (pipe_fds[child_end]);
 186       pipe_fds[child_end] = tmp;
 187     }
 188
 189   if (__posix_spawn_file_actions_adddup2 (&fa, pipe_fds[child_end],
 190       child_pipe_fd) != 0)
 191     goto spawn_failure;
 192
 193 #ifdef _IO_MTSAFE_IO
 194   _IO_cleanup_region_start_noarg (unlock);
 195   _IO_lock_lock (proc_file_chain_lock);
 196 #endif
 197   spawn_ok = spawn_process (&fa, fp, command, do_cloexec, pipe_fds,
 198                             parent_end, child_end, child_pipe_fd);
 199 #ifdef _IO_MTSAFE_IO
 200   _IO_lock_unlock (proc_file_chain_lock);
 201   _IO_cleanup_region_end (0);
 202 #endif
 203
 204   __posix_spawn_file_actions_destroy (&fa);
 205
 206   if (!spawn_ok)
 207     {
 208     spawn_failure:
 209       __close_nocancel (pipe_fds[child_end]);
 210       __close_nocancel (pipe_fds[parent_end]);
 211       __set_errno (ENOMEM);
 212       return NULL;
 213     }
 214
 215   _IO_mask_flags (fp, read_or_write, _IO_NO_READS|_IO_NO_WRITES);
 216   return fp;
 217 }
 218
 219 FILE *
 220 _IO_new_popen (const char *command, const char *mode)
 221 {
 222   struct locked_FILE
 223   {
 224     struct _IO_proc_file fpx;
 225 #ifdef _IO_MTSAFE_IO
 226     _IO_lock_t lock;
 227 #endif
 228   } *new_f;
 229   FILE *fp;
 230
 231   new_f = (struct locked_FILE *) malloc (sizeof (struct locked_FILE));
 232   if (new_f == NULL)
 233     return NULL;
 234 #ifdef _IO_MTSAFE_IO
 235   new_f->fpx.file.file._lock = &new_f->lock;
 236 #endif
 237   fp = &new_f->fpx.file.file;
 238   _IO_init_internal (fp, 0);
 239   _IO_JUMPS (&new_f->fpx.file) = &_IO_proc_jumps;
 240   _IO_new_file_init_internal (&new_f->fpx.file);
 241   if (_IO_new_proc_open (fp, command, mode) != NULL)
 242     return (FILE *) &new_f->fpx.file;
 243   _IO_un_link (&new_f->fpx.file);
 244   free (new_f);
 245   return NULL;
 246 }
 247
 248 int
 249 _IO_new_proc_close (FILE *fp)
 250 {
 251   /* This is not name-space clean. FIXME! */
 252   int wstatus;
 253   _IO_proc_file **ptr = &proc_file_chain;
 254   pid_t wait_pid;
 255   int status = -1;
 256
 257   /* Unlink from proc_file_chain. */
 258 #ifdef _IO_MTSAFE_IO
 259   _IO_cleanup_region_start_noarg (unlock);
 260   _IO_lock_lock (proc_file_chain_lock);
 261 #endif
 262   for ( ; *ptr != NULL; ptr = &(*ptr)->next)
 263     {
 264       if (*ptr == (_IO_proc_file *) fp)
 265         {
 266           *ptr = (*ptr)->next;
 267           status = 0;
 268           break;
 269         }
 270     }
 271 #ifdef _IO_MTSAFE_IO
 272   _IO_lock_unlock (proc_file_chain_lock);
 273   _IO_cleanup_region_end (0);
 274 #endif
 275
 276   if (status < 0 || __close_nocancel (_IO_fileno(fp)) < 0)
 277     return -1;
 278   /* POSIX.2 Rationale:  "Some historical implementations either block
 279      or ignore the signals SIGINT, SIGQUIT, and SIGHUP while waiting
 280      for the child process to terminate.  Since this behavior is not
 281      described in POSIX.2, such implementations are not conforming." */
 282   do
 283     {
 284       wait_pid = __waitpid_nocancel (((_IO_proc_file *) fp)->pid, &wstatus, 0);
 285     }
 286   while (wait_pid == -1 && errno == EINTR);
 287   if (wait_pid == -1)
 288     return -1;
 289   return wstatus;
 290 }
 291
 292 static const struct _IO_jump_t _IO_proc_jumps libio_vtable = {
 293   JUMP_INIT_DUMMY,
 294   JUMP_INIT(finish, _IO_new_file_finish),
 295   JUMP_INIT(overflow, _IO_new_file_overflow),
 296   JUMP_INIT(underflow, _IO_new_file_underflow),
 297   JUMP_INIT(uflow, _IO_default_uflow),
 298   JUMP_INIT(pbackfail, _IO_default_pbackfail),
 299   JUMP_INIT(xsputn, _IO_new_file_xsputn),
 300   JUMP_INIT(xsgetn, _IO_default_xsgetn),
 301   JUMP_INIT(seekoff, _IO_new_file_seekoff),
 302   JUMP_INIT(seekpos, _IO_default_seekpos),
 303   JUMP_INIT(setbuf, _IO_new_file_setbuf),
 304   JUMP_INIT(sync, _IO_new_file_sync),
 305   JUMP_INIT(doallocate, _IO_file_doallocate),
 306   JUMP_INIT(read, _IO_file_read),
 307   JUMP_INIT(write, _IO_new_file_write),
 308   JUMP_INIT(seek, _IO_file_seek),
 309   JUMP_INIT(close, _IO_new_proc_close),
 310   JUMP_INIT(stat, _IO_file_stat),
 311   JUMP_INIT(showmanyc, _IO_default_showmanyc),
 312   JUMP_INIT(imbue, _IO_default_imbue)
 313 };
 314
 315 strong_alias (_IO_new_popen, __new_popen)
 316 versioned_symbol (libc, _IO_new_popen, _IO_popen, GLIBC_2_1);
 317 versioned_symbol (libc, __new_popen, popen, GLIBC_2_1);
 318 versioned_symbol (libc, _IO_new_proc_open, _IO_proc_open, GLIBC_2_1);
 319 versioned_symbol (libc, _IO_new_proc_close, _IO_proc_close, GLIBC_2_1);