[PATCH v7 5/7] Cygwin: pty: Guard get_winpid_to_hand_over() with attach_mutex

[Takashi Yano]

Currently, attach_mutex is shared only in the same process. As a
result, if the master process of pty attaches to pseudo console
temporarily, get_winpid_to_hand_over() may wrongly find the master
process to hand over the pseudo console. make attach_mutex shared
within the PTY and guard get_winpid_to_hand_over() with it.

Fixes: 1e6c51d74136 ("Cygwin: pty: Reorganize the code path of setting up and closing pcon.")
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
Reviewed-by:
---
 winsup/cygwin/fhandler/pty.cc      | 14 ++++++++++++--
 winsup/cygwin/local_includes/tty.h |  1 +
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/fhandler/pty.cc b/winsup/cygwin/fhandler/pty.cc
index 2a0e0d2f7..0de6ec007 100644
--- a/winsup/cygwin/fhandler/pty.cc
+++ b/winsup/cygwin/fhandler/pty.cc
@@ -774,6 +774,12 @@ fhandler_pty_slave::open (int flags, mode_t)
       errmsg = "open pipe switch mutex failed, %E";
       goto err;
     }
+  if (!(attach_mutex
+	= get_ttyp ()->open_mutex (ATTACH_MUTEX, MAXIMUM_ALLOWED)))
+    {
+      errmsg = "open attach mutex failed, %E";
+      goto err;
+    }
   shared_name (buf, INPUT_AVAILABLE_EVENT, get_minor ());
   if (!(input_available_event = OpenEvent (MAXIMUM_ALLOWED, TRUE, buf)))
     {
@@ -2533,6 +2539,7 @@ void
 fhandler_pty_slave::fixup_after_fork (HANDLE parent)
 {
   create_invisible_console ();
+  attach_mutex = get_ttyp ()->open_mutex (ATTACH_MUTEX, MAXIMUM_ALLOWED);
 
   // fork_fixup (parent, inuse, "inuse");
   // fhandler_pty_common::fixup_after_fork (parent);
@@ -3164,8 +3171,9 @@ fhandler_pty_master::setup ()
   if (!(pipe_sw_mutex = CreateMutex (&sa, FALSE, buf)))
     goto err;
 
-  if (!attach_mutex)
-    attach_mutex = CreateMutex (&sec_none_nih, FALSE, NULL);
+  errstr = shared_name (buf, ATTACH_MUTEX, unit);
+  if (!(attach_mutex = CreateMutex (&sa, FALSE, buf)))
+    goto err;
 
   /* Create master control pipe which allows the master to duplicate
      the pty pipe handles to processes which deserve it. */
@@ -3725,6 +3733,7 @@ fhandler_pty_slave::get_winpid_to_hand_over (tty *ttyp,
       DWORD current_pid = myself->exec_dwProcessId ?: myself->dwProcessId;
       if (ttyp->nat_pipe_owner_pid == GetCurrentProcessId ())
 	current_pid = GetCurrentProcessId ();
+      acquire_attach_mutex (mutex_timeout);
       switch_to = get_console_process_id (current_pid,
 					  false, true, true, true);
       if (!switch_to)
@@ -3733,6 +3742,7 @@ fhandler_pty_slave::get_winpid_to_hand_over (tty *ttyp,
       if (!switch_to && ttyp->pcon_activated)
 	switch_to = get_console_process_id (current_pid,
 					    false, false, false, false);
+      release_attach_mutex ();
     }
   return switch_to;
 }
diff --git a/winsup/cygwin/local_includes/tty.h b/winsup/cygwin/local_includes/tty.h
index cd1e202f1..962697782 100644
--- a/winsup/cygwin/local_includes/tty.h
+++ b/winsup/cygwin/local_includes/tty.h
@@ -22,6 +22,7 @@ details. */
 #define OUTPUT_MUTEX		"cygtty.output.mutex"
 #define INPUT_MUTEX		"cygtty.input.mutex"
 #define PIPE_SW_MUTEX		"cygtty.pipe_sw.mutex"
+#define ATTACH_MUTEX		"cygtty.attach.mutex"
 #define TTY_SLAVE_ALIVE		"cygtty.slave_alive"
 #define TTY_SLAVE_READING	"cygtty.slave_reading"
 
-- 
2.51.0