[newlib-cygwin] Cygwin: fhandler_termios::tcsetpgrp: check that argument is non-negative

[Ken Brown]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=8a46b8ede22d707aae2dc2e0e53cbad3f26f029f

commit 8a46b8ede22d707aae2dc2e0e53cbad3f26f029f
Author: Ken Brown <kbrown@cornell.edu>
Date:   Wed Jul 24 11:29:53 2019 -0400

    Cygwin: fhandler_termios::tcsetpgrp: check that argument is non-negative
    
    Return -1 with EINVAL if pgid < 0.
    
    Previously tcsetpgrp() would blindly go ahead and set the pgid of the
    controlling terminal to a negative value, causing later calls to
    various functions to fail.
    
    For example, gdb has code like the following:
    
      tcsetpgrp (0, getpgid (inf->pid));
    
    If getpgid (inf->pid) fails (returns -1), then this code would set the
    pgid of fd 0 to -1, so that some later calls to getpgid() would also
    return -1.  This caused the problem reported here:
    
      https://cygwin.com/ml/cygwin/2019-07/msg00166.html.

Diff:
---
 winsup/cygwin/fhandler_termios.cc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/winsup/cygwin/fhandler_termios.cc b/winsup/cygwin/fhandler_termios.cc
index 4ce5343..5b0ba56 100644
--- a/winsup/cygwin/fhandler_termios.cc
+++ b/winsup/cygwin/fhandler_termios.cc
@@ -69,6 +69,11 @@ fhandler_termios::tcsetpgrp (const pid_t pgid)
       set_errno (EPERM);
       return -1;
     }
+  else if (pgid < 0)
+    {
+      set_errno (EINVAL);
+      return -1;
+    }
   int res;
   while (1)
     {