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
popen(const char * cmd,const char * mode)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 }
74