src/stdio/popen.c

   1 #include <fcntl.h>
   2 #include <unistd.h>
   3 #include <errno.h>
   4 #include <string.h>
   5 #include <spawn.h>
   6 #include "stdio_impl.h"
   7 #include "syscall.h"
   8
   9 extern char **__environ;
  10
  11 FILE *popen(const char *cmd, const char *mode)
  12 {
  13         int p[2], op, e;
  14         pid_t pid;
  15         FILE *f;
  16         posix_spawn_file_actions_t fa;
  17
  18         if (*mode == 'r') {
  19                 op = 0;
  20         } else if (*mode == 'w') {
  21                 op = 1;
  22         } else {
  23                 errno = EINVAL;
  24                 return 0;
  25         }
  26
  27         if (pipe2(p, O_CLOEXEC)) return NULL;
  28         f = fdopen(p[op], mode);
  29         if (!f) {
  30                 __syscall(SYS_close, p[0]);
  31                 __syscall(SYS_close, p[1]);
  32                 return NULL;
  33         }
  34         FLOCK(f);
  35
  36         /* If the child's end of the pipe happens to already be on the final
  37          * fd number to which it will be assigned (either 0 or 1), it must
  38          * be moved to a different fd. Otherwise, there is no safe way to
  39          * remove the close-on-exec flag in the child without also creating
  40          * a file descriptor leak race condition in the parent. */
  41         if (p[1-op] == 1-op) {
  42                 int tmp = fcntl(1-op, F_DUPFD_CLOEXEC, 0);
  43                 if (tmp < 0) {
  44                         e = errno;
  45                         goto fail;
  46                 }
  47                 __syscall(SYS_close, p[1-op]);
  48                 p[1-op] = tmp;
  49         }
  50
  51         e = ENOMEM;
  52         if (!posix_spawn_file_actions_init(&fa)) {
  53                 if (!posix_spawn_file_actions_adddup2(&fa, p[1-op], 1-op)) {
  54                         if (!(e = posix_spawn(&pid, "/bin/sh", &fa, 0,
  55                             (char *[]){ "sh", "-c", (char *)cmd, 0 }, __environ))) {
  56                                 posix_spawn_file_actions_destroy(&fa);
  57                                 f->pipe_pid = pid;
  58                                 if (!strchr(mode, 'e'))
  59                                         fcntl(p[op], F_SETFD, 0);
  60                                 __syscall(SYS_close, p[1-op]);
  61                                 FUNLOCK(f);
  62                                 return f;
  63                         }
  64                 }
  65                 posix_spawn_file_actions_destroy(&fa);
  66         }
  67 fail:
  68         fclose(f);
  69         __syscall(SYS_close, p[1-op]);
  70
  71         errno = e;
  72         return 0;
  73 }