Ignore pending input before confirmation prompts

Pressing ENTER for too long lets it end up in the input buffer which the
confirmation prompt happily picks up and accepts as confirmation for
deleting potentially half your system or doing other silly things.
Ironically, this confirmation will also be silent in terms of output as
it is likely erased by future progress reporting.

Closes: #1082956

1 files changed, 7 insertions, 0 deletions

diff --git a/apt-private/private-output.cc b/apt-private/private-output.cc
index 4a946f2b8..0c56026a5 100644
--- a/apt-private/private-output.cc
+++ b/apt-private/private-output.cc
@@ -23,6 +23,7 @@
 #include <langinfo.h>
 #include <regex.h>
 #include <sys/ioctl.h>
+#include <termios.h>
 #include <unistd.h>
 
 #include <sstream>
@@ -809,6 +810,12 @@ bool YnPrompt(char const * const Question, bool const Default, bool const ShowGl
       else
 	 _error->DumpErrors(c2o, GlobalError::NOTICE);
    }
+   // ignore pending input on terminal
+   if (not AssumeYes && not AssumeNo && isatty(STDIN_FILENO) == 1)
+   {
+      tcflush(STDIN_FILENO, TCIFLUSH);
+      std::cin.clear();
+   }
 
    c2o << Question << std::flush;