114 lines
3.8 KiB
C
114 lines
3.8 KiB
C
/*
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* child.c
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* Copyright (C) 2018 Kovid Goyal <kovid at kovidgoyal.net>
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*
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* Distributed under terms of the GPL3 license.
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*/
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#include "data-types.h"
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#include <unistd.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <errno.h>
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#include <string.h>
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static inline char**
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serialize_string_tuple(PyObject *src) {
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Py_ssize_t sz = PyTuple_GET_SIZE(src);
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char **ans = calloc(sz + 1, sizeof(char*));
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if (!ans) fatal("Out of memory");
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for (Py_ssize_t i = 0; i < sz; i++) ans[i] = PyUnicode_AsUTF8(PyTuple_GET_ITEM(src, i));
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return ans;
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}
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extern char **environ;
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static inline void
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write_to_stderr(const char *text) {
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size_t sz = strlen(text);
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size_t written = 0;
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while(written < sz) {
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ssize_t amt = write(2, text + written, sz - written);
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if (amt == 0) break;
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if (amt < 0) {
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if (errno == EAGAIN || errno == EINTR) continue;
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break;
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}
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written += amt;
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}
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}
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static PyObject*
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spawn(PyObject *self UNUSED, PyObject *args) {
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PyObject *argv_p, *env_p;
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int master, slave, stdin_read_fd, stdin_write_fd;
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char *cwd, *exe;
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if (!PyArg_ParseTuple(args, "ssO!O!iiii", &exe, &cwd, &PyTuple_Type, &argv_p, &PyTuple_Type, &env_p, &master, &slave, &stdin_read_fd, &stdin_write_fd)) return NULL;
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char name[2048] = {0};
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if (ttyname_r(slave, name, sizeof(name) - 1) != 0) { PyErr_SetFromErrno(PyExc_OSError); return NULL; }
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char **argv = serialize_string_tuple(argv_p);
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char **env = serialize_string_tuple(env_p);
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#define exit_on_err(m) { write_to_stderr(m); write_to_stderr(": "); write_to_stderr(strerror(errno)); exit(EXIT_FAILURE); }
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pid_t pid = fork();
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switch(pid) {
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case 0:
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// child
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// Use only signal-safe functions (man 7 signal-safety)
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if (chdir(cwd) != 0) { if (chdir("/") != 0) {} }; // ignore failure to chdir to /
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if (setsid() == -1) exit_on_err("setsid() in child process failed");
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if (dup2(slave, 1) == -1) exit_on_err("dup2() failed for fd number 1");
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if (dup2(slave, 2) == -1) exit_on_err("dup2() failed for fd number 2");
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if (stdin_read_fd > -1) {
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if (dup2(stdin_read_fd, 0) == -1) exit_on_err("dup2() failed for fd number 0");
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close(stdin_read_fd);
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close(stdin_write_fd);
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} else {
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if (dup2(slave, 0) == -1) exit_on_err("dup2() failed for fd number 0");
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}
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close(slave);
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close(master);
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for (int c = 3; c < 201; c++) close(c);
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// Establish the controlling terminal (see man 7 credentials)
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int tfd = open(name, O_RDWR);
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if (tfd == -1) exit_on_err("Failed to open controlling terminal");
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close(tfd);
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environ = env;
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execvp(exe, argv);
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// Report the failure and exec a shell instead, so that we are not left
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// with a forked but not exec'ed process
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write_to_stderr("Failed to launch child: ");
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write_to_stderr(argv[0]);
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write_to_stderr("\nWith error: ");
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write_to_stderr(strerror(errno));
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write_to_stderr("\nPress Enter to exit.\n");
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execlp("sh", "sh", "-c", "read w", NULL);
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exit(EXIT_FAILURE);
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break;
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case -1:
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PyErr_SetFromErrno(PyExc_OSError);
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break;
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default:
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break;
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}
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#undef exit_on_err
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free(argv);
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free(env);
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if (PyErr_Occurred()) return NULL;
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return PyLong_FromLong(pid);
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}
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static PyMethodDef module_methods[] = {
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METHODB(spawn, METH_VARARGS),
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{NULL, NULL, 0, NULL} /* Sentinel */
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};
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bool
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init_child(PyObject *module) {
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if (PyModule_AddFunctions(module, module_methods) != 0) return false;
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return true;
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}
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