[newlib-cygwin] Cygwin: pty: Prevent potential errno overwriting.

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=2379142bc5d345421acb9e3ac86abcad0d7bf71e

commit 2379142bc5d345421acb9e3ac86abcad0d7bf71e
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Mon Feb 10 20:42:45 2020 +0900

    Cygwin: pty: Prevent potential errno overwriting.
    
    - In push_to_pcon_screenbuffer(), open() and ioctl() are called.
      Since push_to_pcon_screenbuffer() is called in read() and write(),
      errno which is set in read() and write() code may be overwritten
      in open() or ioctl() call. This patch prevent this situation.

Diff:
---
 winsup/cygwin/fhandler_tty.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/winsup/cygwin/fhandler_tty.cc b/winsup/cygwin/fhandler_tty.cc
index 260776a..cfd4b1c 100644
--- a/winsup/cygwin/fhandler_tty.cc
+++ b/winsup/cygwin/fhandler_tty.cc
@@ -1412,10 +1412,13 @@ fhandler_pty_slave::push_to_pcon_screenbuffer (const char *ptr, size_t len,
   while (!GetConsoleMode (get_output_handle (), &dwMode))
     {
       termios_printf ("GetConsoleMode failed, %E");
+      int errno_save = errno;
       /* Re-open handles */
       this->open (0, 0);
       /* Fix pseudo console window size */
       this->ioctl (TIOCSWINSZ, &get_ttyp ()->winsize);
+      if (errno != errno_save)
+	set_errno (errno_save);
       if (++retry_count > 3)
 	goto cleanup;
     }