From 9ef8927f45f2f8e365cda7cda81c079f29b8ad74 Mon Sep 17 00:00:00 2001 From: Colin Ian King Date: Sat, 30 Mar 2019 00:46:28 +0000 Subject: [PATCH] n_tty: check for negative and zero space return from tty_write_room The return from tty_write_room could potentially be negative if a tty write_room driver returns an error number (not that any seem to do). Rather than just check for a zero return, also check for a -ve return. This avoids the unsigned nr being set to a large unsigned value on the assignment from variable space and can lead to overflowing the buffer buf. Better to be safe than assume all write_room implementations in tty drivers are going to do the right thing. Signed-off-by: Colin Ian King Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_tty.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 9cdb0fa3c4bf..f9c584244f72 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -550,9 +550,9 @@ static ssize_t process_output_block(struct tty_struct *tty, mutex_lock(&ldata->output_lock); space = tty_write_room(tty); - if (!space) { + if (space <= 0) { mutex_unlock(&ldata->output_lock); - return 0; + return space; } if (nr > space) nr = space;