sandbox: handle SIGTTOU and SIGTTIN to avoid hangs

Library/Homebrew/sandbox.rb

@@ -115,17 +115,25 @@ class Sandbox
         end
 
         write_to_pty = proc do
+          # Don't hang if stdin is not able to be used - throw EIO instead.
+          old_ttin = trap(:TTIN, "IGNORE")
+
           # Update the window size whenever the parent terminal's window size changes.
           old_winch = trap(:WINCH, &winch)
           winch.call(nil)
 
-          stdin_thread = Thread.new { IO.copy_stream($stdin, w) }
+          stdin_thread = Thread.new do
+            IO.copy_stream($stdin, w)
+          rescue Errno::EIO
+            # stdin is unavailable - move on.
+          end
 
           r.each_char { |c| print(c) }
 
           Process.wait(pid)
         ensure
           stdin_thread&.kill
+          trap(:TTIN, old_ttin)
           trap(:WINCH, old_winch)
         end
 
@@ -134,7 +142,13 @@ class Sandbox
           # mode while we copy the input/output of the process spawned in the
           # PTY. After we've finished copying to/from the PTY process, io.raw
           # will restore the stdin TTY to its original state.
+          begin
+            # Ignore SIGTTOU as setting raw mode will hang if the process is in the background.
+            old_ttou = trap(:TTOU, "IGNORE")
             $stdin.raw(&write_to_pty)
+          ensure
+            trap(:TTOU, old_ttou)
+          end
         else
           write_to_pty.call
         end