Commit 03c3e977 authored Aug 23, 2021 by Nguyen Dinh Phi Committed by Greg Kroah-Hartman Sep 15, 2021

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 <jirislaby@kernel.org>
Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
Link: https://lore.kernel.org/r/20210823000641.2082292-1-phind.uet@gmail.com


Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 7a25a0a9

drivers/tty/tty_io.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -2176,8 +2176,6 @@ 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)
		@@ -2193,8 +2191,10 @@ 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;
		}