unix: open ttyname instead of /dev/tty

Find the real name of the tty using ttyname_r(3) instead of
opening "/dev/tty" which causes trouble if the fd doesn't point to the
controlling terminal.

PR-URL: https://github.com/libuv/libuv/pull/779
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>

Makefile.am

@@ -129,6 +129,7 @@ EXTRA_DIST = test/fixtures/empty_file \
 TESTS = test/run-tests
 check_PROGRAMS = test/run-tests
 test_run_tests_CFLAGS =
+test_run_tests_LDFLAGS =
 test_run_tests_SOURCES = test/blackhole-server.c \
                          test/dns-server.c \
                          test/echo-server.c \
@@ -303,15 +304,18 @@ libuv_la_SOURCES += src/unix/darwin.c \
                     src/unix/fsevents.c \
                     src/unix/kqueue.c \
                     src/unix/proctitle.c
+test_run_tests_LDFLAGS += -lutil
 endif
 
 if DRAGONFLY
 include_HEADERS += include/uv-bsd.h
+test_run_tests_LDFLAGS += -lutil
 endif
 
 if FREEBSD
 include_HEADERS += include/uv-bsd.h
 libuv_la_SOURCES += src/unix/freebsd.c src/unix/kqueue.c
+test_run_tests_LDFLAGS += -lutil
 endif
 
 if LINUX
@@ -322,16 +326,19 @@ libuv_la_SOURCES += src/unix/linux-core.c \
                     src/unix/linux-syscalls.c \
                     src/unix/linux-syscalls.h \
                     src/unix/proctitle.c
+test_run_tests_LDFLAGS += -lutil
 endif
 
 if NETBSD
 include_HEADERS += include/uv-bsd.h
 libuv_la_SOURCES += src/unix/kqueue.c src/unix/netbsd.c
+test_run_tests_LDFLAGS += -lutil
 endif
 
 if OPENBSD
 include_HEADERS += include/uv-bsd.h
 libuv_la_SOURCES += src/unix/kqueue.c src/unix/openbsd.c
+test_run_tests_LDFLAGS += -lutil
 endif
 
 if SUNOS

docs/src/tty.rst

@@ -58,14 +58,22 @@ API
     `readable`, specifies if you plan on calling :c:func:`uv_read_start` with
     this stream. stdin is readable, stdout is not.
 
-    On Unix this function will try to open ``/dev/tty`` and use it if the passed
-    file descriptor refers to a TTY. This lets libuv put the tty in non-blocking
-    mode without affecting other processes that share the tty.
+    On Unix this function will determine the path of the fd of the terminal
+    using :man:`ttyname_r(3)`, open it, and use it if the passed file descriptor
+    refers to a TTY. This lets libuv put the tty in non-blocking mode without
+    affecting other processes that share the tty.
+
+    This function is not thread safe on systems that don't support
+    ioctl TIOCGPTN or TIOCPTYGNAME, for instance OpenBSD and Solaris.
 
     .. note::
-        If opening ``/dev/tty`` fails, libuv falls back to blocking writes for
+        If reopening the TTY fails, libuv falls back to blocking writes for
         non-readable TTY streams.
 
+    .. versionchanged:: 1.9.0: the path of the TTY is determined by
+                        :man:`ttyname_r(3)`. In earlier versions libuv opened
+                        `/dev/tty` instead.
+
     .. versionchanged:: 1.5.0: trying to initialize a TTY stream with a file
                         descriptor that refers to a file returns `UV_EINVAL`
                         on UNIX.

src/unix/tty.c

@@ -23,6 +23,7 @@
 #include "internal.h"
 #include "spinlock.h"
 
+#include <stdlib.h>
 #include <assert.h>
 #include <unistd.h>
 #include <termios.h>
@@ -33,12 +34,30 @@ static int orig_termios_fd = -1;
 static struct termios orig_termios;
 static uv_spinlock_t termios_spinlock = UV_SPINLOCK_INITIALIZER;
 
+static int uv__tty_is_slave(const int fd) {
+  int result;
+#if defined(__linux__) || defined(__FreeBSD__)
+  int dummy;
+
+  result = ioctl(fd, TIOCGPTN, &dummy) != 0;
+#elif defined(__APPLE__)
+  char dummy[256];
+
+  result = ioctl(fd, TIOCPTYGNAME, &dummy) != 0;
+#else
+  /* Fallback to ptsname
+   */
+  result = ptsname(fd) == NULL;
+#endif
+  return result;
+}
 
 int uv_tty_init(uv_loop_t* loop, uv_tty_t* tty, int fd, int readable) {
   uv_handle_type type;
   int flags;
   int newfd;
   int r;
+  char path[256];
 
   /* File descriptors that refer to files cannot be monitored with epoll.
    * That restriction also applies to character devices like /dev/random
@@ -62,7 +81,15 @@ int uv_tty_init(uv_loop_t* loop, uv_tty_t* tty, int fd, int readable) {
    * other processes.
    */
   if (type == UV_TTY) {
-    r = uv__open_cloexec("/dev/tty", O_RDWR);
+    /* Reopening a pty in master mode won't work either because the reopened
+     * pty will be in slave mode (*BSD) or reopening will allocate a new
+     * master/slave pair (Linux). Therefore check if the fd points to a
+     * slave device.
+     */
+    if (uv__tty_is_slave(fd) && ttyname_r(fd, path, sizeof(path)) == 0)
+      r = uv__open_cloexec(path, O_RDWR);
+    else
+      r = -1;
 
     if (r < 0) {
       /* fallback to using blocking writes */

test/test-list.h

@@ -44,6 +44,7 @@ TEST_DECLARE   (semaphore_2)
 TEST_DECLARE   (semaphore_3)
 TEST_DECLARE   (tty)
 TEST_DECLARE   (tty_file)
+TEST_DECLARE   (tty_pty)
 TEST_DECLARE   (stdio_over_pipes)
 TEST_DECLARE   (ip6_pton)
 TEST_DECLARE   (ipc_listen_before_write)
@@ -387,6 +388,7 @@ TASK_LIST_START
   TEST_ENTRY  (pipe_set_non_blocking)
   TEST_ENTRY  (tty)
   TEST_ENTRY  (tty_file)
+  TEST_ENTRY  (tty_pty)
   TEST_ENTRY  (stdio_over_pipes)
   TEST_ENTRY  (ip6_pton)
   TEST_ENTRY  (ipc_listen_before_write)

test/test-tty.c

@@ -28,6 +28,13 @@
 #else /*  Unix */
 # include <fcntl.h>
 # include <unistd.h>
+# if defined(__linux__)
+#  include <pty.h>
+# elif defined(__OpenBSD__) || defined(__NetBSD__) || defined(__APPLE__)
+#  include <util.h>
+# elif defined(__FreeBSD__) || defined(__DragonFly__)
+#  include <libutil.h>
+# endif
 #endif
 
 #include <string.h>
@@ -182,3 +189,35 @@ TEST_IMPL(tty_file) {
 #endif
   return 0;
 }
+
+TEST_IMPL(tty_pty) {
+# if defined(__linux__) || defined(__OpenBSD__) || defined(__NetBSD__) || \
+    defined(__APPLE__) || defined(__FreeBSD__) || defined(__DragonFly__)
+  int master_fd, slave_fd;
+  struct winsize w;
+  uv_loop_t loop;
+  uv_tty_t master_tty, slave_tty;
+
+  ASSERT(0 == uv_loop_init(&loop));
+
+  ASSERT(0 == openpty(&master_fd, &slave_fd, NULL, NULL, &w));
+  ASSERT(0 == uv_tty_init(&loop, &slave_tty, slave_fd, 0));
+  ASSERT(0 == uv_tty_init(&loop, &master_tty, master_fd, 0));
+  /* Check if the file descriptor was reopened. If it is,
+   * UV_STREAM_BLOCKING (value 0x80) isn't set on flags.
+   */
+  ASSERT(0 == (slave_tty.flags & 0x80));
+  /* The master_fd of a pty should never be reopened.
+   */
+  ASSERT(master_tty.flags & 0x80);
+  ASSERT(0 == close(slave_fd));
+  uv_close((uv_handle_t*) &slave_tty, NULL);
+  ASSERT(0 == close(master_fd));
+  uv_close((uv_handle_t*) &master_tty, NULL);
+
+  ASSERT(0 == uv_run(&loop, UV_RUN_DEFAULT));
+
+  MAKE_VALGRIND_HAPPY();
+#endif
+  return 0;
+}

uv.gyp

@@ -426,6 +426,11 @@
             'test/runner-unix.h',
           ],
         }],
+        [ 'OS in "mac dragonflybsd freebsd linux netbsd openbsd".split()', {
+          'link_settings': {
+            'libraries': [ '-lutil' ],
+          },
+        }],
         [ 'OS=="solaris"', { # make test-fs.c compile, needs _POSIX_C_SOURCE
           'defines': [
             '__EXTENSIONS__',