[newlib-cygwin] Cygwin: console: Do not unmap shared console memory belonging to ctty.

[Takashi Yano]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=c77a5689f7bd4520f6d87481fd08591747b5da0f

commit c77a5689f7bd4520f6d87481fd08591747b5da0f
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Fri Mar 1 19:05:36 2024 +0900

    Cygwin: console: Do not unmap shared console memory belonging to ctty.
    
    In the condition that console setup for CTTY and close run at the
    sametime, accessing shared console memory which is already unmapped
    may occur. With this patch, to avoid this race issue, shared console
    memory which belongs to contorolling terminal (CTTY) is kept mapped
    as before.
    Addresses: https://cygwin.com/pipermail/cygwin/2024-February/255561.html
    
    Fixes: 3721a756b0d8 ("Cygwin: console: Make the console accessible from other terminals.")
    Reported-by: Kate Deplaix <kit-ty-kate@outlook.com>
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

Diff:
---
 winsup/cygwin/fhandler/console.cc | 8 +++++---
 winsup/cygwin/release/3.5.2       | 7 +++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/winsup/cygwin/fhandler/console.cc b/winsup/cygwin/fhandler/console.cc
index c16ca3962..67ea95466 100644
--- a/winsup/cygwin/fhandler/console.cc
+++ b/winsup/cygwin/fhandler/console.cc
@@ -1926,9 +1926,11 @@ fhandler_console::close ()
 	  || get_device () == (dev_t) myself->ctty))
     free_console ();
 
-  if (shared_console_info[unit])
-    UnmapViewOfFile ((void *) shared_console_info[unit]);
-  shared_console_info[unit] = NULL;
+  if (shared_console_info[unit] && myself->ctty != tc ()->ntty)
+    {
+      UnmapViewOfFile ((void *) shared_console_info[unit]);
+      shared_console_info[unit] = NULL;
+    }
 
   return 0;
 }
diff --git a/winsup/cygwin/release/3.5.2 b/winsup/cygwin/release/3.5.2
new file mode 100644
index 000000000..7d8df9489
--- /dev/null
+++ b/winsup/cygwin/release/3.5.2
@@ -0,0 +1,7 @@
+Fixes:
+------
+
+- Fix the problem that console setup accesses shared memory which
+  is already unmapped due to race condition. To avoid this issue,
+  shared console memory will be kept mapped if it belongs to CTTY.
+  Addresses:  https://cygwin.com/pipermail/cygwin/2024-February/255561.html