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Remove a few more signal unsafe function calls between fork() and exec()

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Kovid Goyal
2018-01-05 00:24:15 +05:30
parent aa107956f9
commit e03c713294
1 changed files with 32 additions and 13 deletions
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45
kitty/child.c
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@@ -23,54 +23,73 @@ serialize_string_tuple(PyObject *src) {
extern char **environ;
static inline void
write_to_stderr(const char *text) {
size_t sz = strlen(text);
size_t written = 0;
while(written < sz) {
ssize_t amt = write(2, text + written, sz - written);
if (amt == 0) break;
if (amt < 0) {
if (errno == EAGAIN || errno == EINTR) continue;
break;
}
written += amt;
}
}
static PyObject*
spawn(PyObject *self UNUSED, PyObject *args) {
PyObject *argv_p, *env_p;
int master, slave, stdin_read_fd, stdin_write_fd;
char* cwd;
if (!PyArg_ParseTuple(args, "sO!O!iiii", &cwd, &PyTuple_Type, &argv_p, &PyTuple_Type, &env_p, &master, &slave, &stdin_read_fd, &stdin_write_fd)) return NULL;
char name[2048] = {0};
if (ttyname_r(slave, name, sizeof(name) - 1) != 0) { PyErr_SetFromErrno(PyExc_OSError); return NULL; }
char **argv = serialize_string_tuple(argv_p);
char **env = serialize_string_tuple(env_p);
#define exit_on_err(m) { write_to_stderr(m); write_to_stderr(": "); write_to_stderr(strerror(errno)); exit(EXIT_FAILURE); }
pid_t pid = fork();
if (pid == 0) {
// child
// We cannot use malloc before exec() as it might deadlock if a thread in the parent process is in the middle of a malloc itself
// Use only signal-safe functions (man 7 signal-safety)
if (chdir(cwd) != 0) { if (chdir("/") != 0) {} }; // ignore failure to chdir to /
if (setsid() == -1) { perror("setsid() in child process failed"); exit(EXIT_FAILURE); }
if (dup2(slave, 1) == -1) { perror("dup2() failed for fd number 1"); exit(EXIT_FAILURE); }
if (dup2(slave, 2) == -1) { perror("dup2() failed for fd number 2"); exit(EXIT_FAILURE); }
if (setsid() == -1) exit_on_err("setsid() in child process failed");
if (dup2(slave, 1) == -1) exit_on_err("dup2() failed for fd number 1");
if (dup2(slave, 2) == -1) exit_on_err("dup2() failed for fd number 2");
if (stdin_read_fd > -1) {
if (dup2(stdin_read_fd, 0) == -1) { perror("dup2() failed for fd number 0"); exit(EXIT_FAILURE); }
if (dup2(stdin_read_fd, 0) == -1) exit_on_err("dup2() failed for fd number 0");
close(stdin_read_fd);
close(stdin_write_fd);
} else {
if (dup2(slave, 0) == -1) { perror("dup2() failed for fd number 0"); exit(EXIT_FAILURE); }
if (dup2(slave, 0) == -1) exit_on_err("dup2() failed for fd number 0");
}
close(slave);
close(master);
for (int c = 3; c < 201; c++) close(c);
// Establish the controlling terminal (see man 7 credentials)
char *name = ttyname(1);
if (name == NULL) { perror("Failed to call ttyname()"); exit(EXIT_FAILURE); }
int tfd = open(name, O_RDWR);
if (tfd == -1) { perror("Failed to open controlling terminal"); exit(EXIT_FAILURE); }
if (tfd == -1) exit_on_err("Failed to open controlling terminal");
close(tfd);
environ = env;
execvp(argv[0], argv);
// Report the failure and exec a shell instead, so that we are not left
// with a forked but not execed process
fprintf(stderr, "Failed to launch child: %s\nWith error: %s [%d]\n", argv[0], strerror(errno), errno);
fprintf(stderr, "Press Enter to exit.\n");
fflush(stderr);
// with a forked but not exec'ed process
write_to_stderr("Failed to launch child: ");
write_to_stderr(argv[0]);
write_to_stderr("\nWith error: ");
write_to_stderr(strerror(errno));
write_to_stderr("\nPress Enter to exit.\n");
execlp("sh", "sh", "-c", "read w", NULL);
exit(EXIT_FAILURE);
} else {
free(argv);
free(env);
}
#undef exit_on_err
return PyLong_FromLong(pid);
}