tty: flush flip buffer on ldisc input queue flush

Flush the tty flip buffer when the line discipline input queue is flushed,
including the user call tcflush(TCIFLUSH/TCIOFLUSH).  This prevents
unexpected stale data after a user application calls tcflush().

Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Antonino Ingargiola <tritemio@gmail.com>
Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index bc849957508d..75d2a46e106f 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -369,6 +369,29 @@ static void tty_buffer_free(struct tty_struct *tty, struct tty_buffer *b)
 }
 
 /**
+ *      tty_buffer_flush                -       flush full tty buffers
+ *      @tty: tty to flush
+ *
+ *      flush all the buffers containing receive data
+ *
+ *      Locking: none
+ */
+
+static void tty_buffer_flush(struct tty_struct *tty)
+{
+        struct tty_buffer *thead;
+        unsigned long flags;
+
+        spin_lock_irqsave(&tty->buf.lock, flags);
+        while((thead = tty->buf.head) != NULL) {
+                tty->buf.head = thead->next;
+                tty_buffer_free(tty, thead);
+        }
+        tty->buf.tail = NULL;
+        spin_unlock_irqrestore(&tty->buf.lock, flags);
+}
+
+/**
  *      tty_buffer_find         -       find a free tty buffer
  *      @tty: tty owning the buffer
  *      @size: characters wanted
@@ -1248,6 +1271,7 @@ void tty_ldisc_flush(struct tty_struct *tty)
                         ld->flush_buffer(tty);
                 tty_ldisc_deref(ld);
         }
+        tty_buffer_flush(tty);
 }
 
 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
@@ -3350,6 +3374,15 @@ int tty_ioctl(struct inode * inode, struct file * file,
                 case TIOCMBIC:
                 case TIOCMBIS:
                         return tty_tiocmset(tty, file, cmd, p);
+                case TCFLSH:
+                        switch (arg) {
+                        case TCIFLUSH:
+                        case TCIOFLUSH:
+                                /* flush tty buffer and allow ldisc to process ioctl */
+                                tty_buffer_flush(tty);
+                                break;
+                        }
+                        break;
         }
         if (tty->driver->ioctl) {
                 retval = (tty->driver->ioctl)(tty, file, cmd, arg);