n_tty: Fix EOF push handling

In canonical mode, an EOF which is not the first character of the line
causes read() to complete and return the number of characters read so
far (commonly referred to as EOF push). However, if the previous read()
returned because the user buffer was full _and_ the next character
is an EOF not at the beginning of the line, read() must not return 0,
thus mistakenly indicating the end-of-file condition.

The TTY_PUSH flag is used to indicate an EOF was received which is not
at the beginning of the line. Because the EOF push condition is
evaluated by a thread other than the read(), multiple EOF pushes can
cause a premature end-of-file to be indicated.

Instead, discover the 'EOF push as first read character' condition
from the read() thread itself, and restart the i/o loop if detected.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 0 insertions, 1 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 1b32da6f6cdd..2174698dd6f7 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -664,7 +664,6 @@ static void __tty_hangup(struct tty_struct *tty, int exit_session)
 
         spin_lock_irq(&tty->ctrl_lock);
         clear_bit(TTY_THROTTLED, &tty->flags);
-        clear_bit(TTY_PUSH, &tty->flags);
         clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
         put_pid(tty->session);
         put_pid(tty->pgrp);