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