1 #include <fcntl.h>
2 #include <unistd.h>
3 #include <errno.h>
4 #include <string.h>
5 #include <spawn.h>
6 #include <unsupported_api.h>
7 #include "stdio_impl.h"
8 #include "syscall.h"
9
10 extern char **__environ;
11
popen(const char * cmd,const char * mode)12 FILE *popen(const char *cmd, const char *mode)
13 {
14 int p[2], op, e;
15 pid_t pid;
16 FILE *f;
17 posix_spawn_file_actions_t fa;
18
19 unsupported_api(__FUNCTION__);
20 if (*mode == 'r') {
21 op = 0;
22 } else if (*mode == 'w') {
23 op = 1;
24 } else {
25 errno = EINVAL;
26 return 0;
27 }
28
29 if (pipe2(p, O_CLOEXEC)) return NULL;
30 f = fdopen(p[op], mode);
31 if (!f) {
32 __syscall(SYS_close, p[0]);
33 __syscall(SYS_close, p[1]);
34 return NULL;
35 }
36 FLOCK(f);
37
38 /* If the child's end of the pipe happens to already be on the final
39 * fd number to which it will be assigned (either 0 or 1), it must
40 * be moved to a different fd. Otherwise, there is no safe way to
41 * remove the close-on-exec flag in the child without also creating
42 * a file descriptor leak race condition in the parent. */
43 if (p[1-op] == 1-op) {
44 int tmp = fcntl(1-op, F_DUPFD_CLOEXEC, 0);
45 if (tmp < 0) {
46 e = errno;
47 goto fail;
48 }
49 __syscall(SYS_close, p[1-op]);
50 p[1-op] = tmp;
51 }
52
53 e = ENOMEM;
54 if (!posix_spawn_file_actions_init(&fa)) {
55 if (!posix_spawn_file_actions_adddup2(&fa, p[1-op], 1-op)) {
56 if (!(e = posix_spawn(&pid, "/bin/sh", &fa, 0,
57 (char *[]){ "sh", "-c", (char *)cmd, 0 }, __environ))) {
58 posix_spawn_file_actions_destroy(&fa);
59 f->pipe_pid = pid;
60 if (!strchr(mode, 'e'))
61 fcntl(p[op], F_SETFD, 0);
62 __syscall(SYS_close, p[1-op]);
63 FUNLOCK(f);
64 return f;
65 }
66 }
67 posix_spawn_file_actions_destroy(&fa);
68 }
69 fail:
70 fclose(f);
71 __syscall(SYS_close, p[1-op]);
72
73 errno = e;
74 return 0;
75 }
76