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