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
9extern char **__environ;
10
11FILE *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	}
67fail:
68	fclose(f);
69	__syscall(SYS_close, p[1-op]);
70
71	errno = e;
72	return 0;
73}
74