bpo-41818: Add os.login_tty() for *nix. (#29658)

* Add `os.login_tty(fd)` for Unix.

Reviewed-by: Christian Heimes <christian@python.org>
Signed-off-by: Gregory P. Smith [Google LLC] <greg@krypto.org>

Doc/library/os.rst

@@ -1000,6 +1000,17 @@ as internal buffering of data.
    .. versionadded:: 3.3
 
 
+.. function:: login_tty(fd)
+
+   Prepare the tty of which fd is a file descriptor for a new login session.
+   Make the calling process a session leader; make the tty the controlling tty,
+   the stdin, the stdout, and the stderr of the calling process; close fd.
+
+   .. availability:: Unix.
+
+   .. versionadded:: 3.11
+
+
 .. function:: lseek(fd, pos, how)
 
    Set the current position of file descriptor *fd* to position *pos*, modified

Misc/NEWS.d/next/Library/2022-05-02-03-56-50.gh-issue-85984.RBivvc.rst

@@ -0,0 +1 @@
+New function os.login_tty() for Unix.

Modules/clinic/posixmodule.c.h

@@ -3106,6 +3106,41 @@ os_openpty(PyObject *module, PyObject *Py_UNUSED(ignored))
 
 #endif /* (defined(HAVE_OPENPTY) || defined(HAVE__GETPTY) || defined(HAVE_DEV_PTMX)) */
 
+#if (defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY))
+
+PyDoc_STRVAR(os_login_tty__doc__,
+"login_tty($module, fd, /)\n"
+"--\n"
+"\n"
+"Prepare the tty of which fd is a file descriptor for a new login session.\n"
+"\n"
+"Make the calling process a session leader; make the tty the\n"
+"controlling tty, the stdin, the stdout, and the stderr of the\n"
+"calling process; close fd.");
+
+#define OS_LOGIN_TTY_METHODDEF    \
+    {"login_tty", (PyCFunction)os_login_tty, METH_O, os_login_tty__doc__},
+
+static PyObject *
+os_login_tty_impl(PyObject *module, int fd);
+
+static PyObject *
+os_login_tty(PyObject *module, PyObject *arg)
+{
+    PyObject *return_value = NULL;
+    int fd;
+
+    if (!_PyLong_FileDescriptor_Converter(arg, &fd)) {
+        goto exit;
+    }
+    return_value = os_login_tty_impl(module, fd);
+
+exit:
+    return return_value;
+}
+
+#endif /* (defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY)) */
+
 #if defined(HAVE_FORKPTY)
 
 PyDoc_STRVAR(os_forkpty__doc__,
@@ -8932,6 +8967,10 @@ exit:
     #define OS_OPENPTY_METHODDEF
 #endif /* !defined(OS_OPENPTY_METHODDEF) */
 
+#ifndef OS_LOGIN_TTY_METHODDEF
+    #define OS_LOGIN_TTY_METHODDEF
+#endif /* !defined(OS_LOGIN_TTY_METHODDEF) */
+
 #ifndef OS_FORKPTY_METHODDEF
     #define OS_FORKPTY_METHODDEF
 #endif /* !defined(OS_FORKPTY_METHODDEF) */
@@ -9331,4 +9370,4 @@ exit:
 #ifndef OS_WAITSTATUS_TO_EXITCODE_METHODDEF
     #define OS_WAITSTATUS_TO_EXITCODE_METHODDEF
 #endif /* !defined(OS_WAITSTATUS_TO_EXITCODE_METHODDEF) */
-/*[clinic end generated code: output=3b5a56add047ee1d input=a9049054013a1b77]*/
+/*[clinic end generated code: output=6150bcc25f5e4bc7 input=a9049054013a1b77]*/

Modules/posixmodule.c

@@ -7274,22 +7274,21 @@ os_sched_getaffinity_impl(PyObject *module, pid_t pid)
 #  define DEV_PTY_FILE "/dev/ptmx"
 #endif
 
-#if defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_DEV_PTMX)
+#if defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_LOGIN_TTY) || defined(HAVE_DEV_PTMX)
 #ifdef HAVE_PTY_H
 #include <pty.h>
-#else
-#ifdef HAVE_LIBUTIL_H
+#ifdef HAVE_UTMP_H
+#include <utmp.h>
+#endif /* HAVE_UTMP_H */
+#elif defined(HAVE_LIBUTIL_H)
 #include <libutil.h>
-#else
-#ifdef HAVE_UTIL_H
+#elif defined(HAVE_UTIL_H)
 #include <util.h>
-#endif /* HAVE_UTIL_H */
-#endif /* HAVE_LIBUTIL_H */
 #endif /* HAVE_PTY_H */
 #ifdef HAVE_STROPTS_H
 #include <stropts.h>
 #endif
-#endif /* defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_DEV_PTMX) */
+#endif /* defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_LOGIN_TTY) || defined(HAVE_DEV_PTMX) */
 
 
 #if defined(HAVE_OPENPTY) || defined(HAVE__GETPTY) || defined(HAVE_DEV_PTMX)
@@ -7392,6 +7391,56 @@ os_openpty_impl(PyObject *module)
 #endif /* defined(HAVE_OPENPTY) || defined(HAVE__GETPTY) || defined(HAVE_DEV_PTMX) */
 
 
+#if defined(HAVE_SETSID) && defined(TIOCSCTTY)
+#define HAVE_FALLBACK_LOGIN_TTY 1
+#endif /* defined(HAVE_SETSID) && defined(TIOCSCTTY) */
+
+#if defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY)
+/*[clinic input]
+os.login_tty
+
+    fd: fildes
+    /
+
+Prepare the tty of which fd is a file descriptor for a new login session.
+
+Make the calling process a session leader; make the tty the
+controlling tty, the stdin, the stdout, and the stderr of the
+calling process; close fd.
+[clinic start generated code]*/
+
+static PyObject *
+os_login_tty_impl(PyObject *module, int fd)
+/*[clinic end generated code: output=495a79911b4cc1bc input=5f298565099903a2]*/
+{
+#ifdef HAVE_LOGIN_TTY
+    if (login_tty(fd) == -1) {
+        return posix_error();
+    }
+#else /* defined(HAVE_FALLBACK_LOGIN_TTY) */
+    /* Establish a new session. */
+    if (setsid() == -1) {
+        return posix_error();
+    }
+
+    /* The tty becomes the controlling terminal. */
+    if (ioctl(fd, TIOCSCTTY, (char *)NULL) == -1) {
+        return posix_error();
+    }
+
+    /* The tty becomes stdin/stdout/stderr */
+    if (dup2(fd, 0) == -1 || dup2(fd, 1) == -1 || dup2(fd, 2) == -1) {
+        return posix_error();
+    }
+    if (fd > 2) {
+        close(fd);
+    }
+#endif /* HAVE_LOGIN_TTY */
+    Py_RETURN_NONE;
+}
+#endif /* defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY) */
+
+
 #ifdef HAVE_FORKPTY
 /*[clinic input]
 os.forkpty
@@ -7427,8 +7476,9 @@ os_forkpty_impl(PyObject *module)
         /* parent: release the import lock. */
         PyOS_AfterFork_Parent();
     }
-    if (pid == -1)
+    if (pid == -1) {
         return posix_error();
+    }
     return Py_BuildValue("(Ni)", PyLong_FromPid(pid), master_fd);
 }
 #endif /* HAVE_FORKPTY */
@@ -14797,6 +14847,7 @@ static PyMethodDef posix_methods[] = {
     OS_SCHED_SETAFFINITY_METHODDEF
     OS_SCHED_GETAFFINITY_METHODDEF
     OS_OPENPTY_METHODDEF
+    OS_LOGIN_TTY_METHODDEF
     OS_FORKPTY_METHODDEF
     OS_GETEGID_METHODDEF
     OS_GETEUID_METHODDEF

configure

@@ -8857,7 +8857,7 @@ for ac_header in  \
   sys/random.h sys/resource.h sys/select.h sys/sendfile.h sys/socket.h sys/soundcard.h sys/stat.h \
   sys/statvfs.h sys/sys_domain.h sys/syscall.h sys/sysmacros.h sys/termio.h sys/time.h sys/times.h \
   sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h sys/xattr.h sysexits.h syslog.h \
-  termios.h util.h utime.h \
+  termios.h util.h utime.h utmp.h \
 
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
@@ -16750,7 +16750,7 @@ fi
 
 
 
-# check for openpty and forkpty
+# check for openpty, login_tty, and forkpty
 
 for ac_func in openpty
 do :
@@ -16849,6 +16849,65 @@ fi
 fi
 done
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for library containing login_tty" >&5
+$as_echo_n "checking for library containing login_tty... " >&6; }
+if ${ac_cv_search_login_tty+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_func_search_save_LIBS=$LIBS
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char login_tty ();
+int
+main ()
+{
+return login_tty ();
+  ;
+  return 0;
+}
+_ACEOF
+for ac_lib in '' util; do
+  if test -z "$ac_lib"; then
+    ac_res="none required"
+  else
+    ac_res=-l$ac_lib
+    LIBS="-l$ac_lib  $ac_func_search_save_LIBS"
+  fi
+  if ac_fn_c_try_link "$LINENO"; then :
+  ac_cv_search_login_tty=$ac_res
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext
+  if ${ac_cv_search_login_tty+:} false; then :
+  break
+fi
+done
+if ${ac_cv_search_login_tty+:} false; then :
+
+else
+  ac_cv_search_login_tty=no
+fi
+rm conftest.$ac_ext
+LIBS=$ac_func_search_save_LIBS
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_search_login_tty" >&5
+$as_echo "$ac_cv_search_login_tty" >&6; }
+ac_res=$ac_cv_search_login_tty
+if test "$ac_res" != no; then :
+  test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
+
+$as_echo "#define HAVE_LOGIN_TTY 1" >>confdefs.h
+
+
+fi
+
 for ac_func in forkpty
 do :
   ac_fn_c_check_func "$LINENO" "forkpty" "ac_cv_func_forkpty"

configure.ac

@@ -2508,7 +2508,7 @@ AC_CHECK_HEADERS([ \
   sys/random.h sys/resource.h sys/select.h sys/sendfile.h sys/socket.h sys/soundcard.h sys/stat.h \
   sys/statvfs.h sys/sys_domain.h sys/syscall.h sys/sysmacros.h sys/termio.h sys/time.h sys/times.h \
   sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h sys/xattr.h sysexits.h syslog.h \
-  termios.h util.h utime.h \
+  termios.h util.h utime.h utmp.h \
 ])
 AC_HEADER_DIRENT
 AC_HEADER_MAJOR
@@ -4670,7 +4670,7 @@ PY_CHECK_FUNC([setgroups], [
 #endif
 ])
 
-# check for openpty and forkpty
+# check for openpty, login_tty, and forkpty
 
 AC_CHECK_FUNCS(openpty,,
    AC_CHECK_LIB(util,openpty,
@@ -4678,6 +4678,9 @@ AC_CHECK_FUNCS(openpty,,
      AC_CHECK_LIB(bsd,openpty, [AC_DEFINE(HAVE_OPENPTY) LIBS="$LIBS -lbsd"])
    )
 )
+AC_SEARCH_LIBS([login_tty], [util],
+ [AC_DEFINE([HAVE_LOGIN_TTY], [1], [Define to 1 if you have the `login_tty' function.])]
+)
 AC_CHECK_FUNCS(forkpty,,
    AC_CHECK_LIB(util,forkpty,
      [AC_DEFINE(HAVE_FORKPTY) LIBS="$LIBS -lutil"],

pyconfig.h.in

@@ -721,6 +721,9 @@
 /* Define to 1 if you have the `log2' function. */
 #undef HAVE_LOG2
 
+/* Define to 1 if you have the `login_tty' function. */
+#undef HAVE_LOGIN_TTY
+
 /* Define to 1 if the system has the type `long double'. */
 #undef HAVE_LONG_DOUBLE
 
@@ -1389,6 +1392,9 @@
 /* Define to 1 if you have the <utime.h> header file. */
 #undef HAVE_UTIME_H
 
+/* Define to 1 if you have the <utmp.h> header file. */
+#undef HAVE_UTMP_H
+
 /* Define to 1 if you have the `uuid_create' function. */
 #undef HAVE_UUID_CREATE