From c2e390c4dff571f73df49836f281be1deb766483 Mon Sep 17 00:00:00 2001 From: Nguyen Dinh Phi Date: Mon, 23 Aug 2021 08:06:41 +0800 Subject: [PATCH] tty: Fix data race between tiocsti() and flush_to_ldisc() commit bb2853a6a421a052268eee00fd5d3f6b3504b2b1 upstream. The ops->receive_buf() may be accessed concurrently from these two functions. If the driver flushes data to the line discipline receive_buf() method while tiocsti() is waiting for the ops->receive_buf() to finish its work, the data race will happen. For example: tty_ioctl |tty_ldisc_receive_buf ->tioctsi | ->tty_port_default_receive_buf | ->tty_ldisc_receive_buf ->hci_uart_tty_receive | ->hci_uart_tty_receive ->h4_recv | ->h4_recv In this case, the h4 receive buffer will be overwritten by the latecomer, and we will lost the data. Hence, change tioctsi() function to use the exclusive lock interface from tty_buffer to avoid the data race. Reported-by: syzbot+97388eb9d31b997fe1d0@syzkaller.appspotmail.com Reviewed-by: Jiri Slaby Signed-off-by: Nguyen Dinh Phi Link: https://lore.kernel.org/r/20210823000641.2082292-1-phind.uet@gmail.com Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 8eaa89b6f55d..aba9557ae45a 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2295,8 +2295,6 @@ static int tty_fasync(int fd, struct file *filp, int on) * Locking: * Called functions take tty_ldiscs_lock * current->signal->tty check is safe without locks - * - * FIXME: may race normal receive processing */ static int tiocsti(struct tty_struct *tty, char __user *p) @@ -2312,8 +2310,10 @@ static int tiocsti(struct tty_struct *tty, char __user *p) ld = tty_ldisc_ref_wait(tty); if (!ld) return -EIO; + tty_buffer_lock_exclusive(tty->port); if (ld->ops->receive_buf) ld->ops->receive_buf(tty, &ch, &mbz, 1); + tty_buffer_unlock_exclusive(tty->port); tty_ldisc_deref(ld); return 0; }