Re: [PATCH] tty: Fix data race between tiocsti() and flush_to_ldisc()
From: Greg KH <gregkh@linuxfoundation.org>
Date: 2021-08-13 07:33:34
Also in:
lkml
On Sun, Aug 08, 2021 at 03:05:13AM +0800, Nguyen Dinh Phi wrote:
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 using the ops->receive_buf(),
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 it cause a memory leak.That looks to be a bug in the h4 code, if the receive_buf() call can not be run at the same time, it should have a lock in it, right?
Hence, change tioctsi() function to use the exclusive lock interface from tty_buffer to avoid the data race.
Where is the lock being grabbed from the other receive_buf() call path to ensure that the lock is always needed here?
quoted hunk ↗ jump to hunk
Signed-off-by: Nguyen Dinh Phi <redacted> Reported-by: syzbot+97388eb9d31b997fe1d0@syzkaller.appspotmail.com --- drivers/tty/tty_io.c | 2 ++ 1 file changed, 2 insertions(+)diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index e8532006e960..746fe13a2054 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c@@ -2307,8 +2307,10 @@ 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);
Did this fix the syzbot reported issue? thanks, greg k-h _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees