diff options
authorNguyen Dinh Phi <phind.uet@gmail.com>2021-08-23 08:06:41 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-09-15 09:47:39 +0200
commit03c3e977eeacbaa9929d5e15fe6908523909543c (patch)
parent7a25a0a94c8b49759582ac6141c06af4f3e8ae8f (diff)
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>
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index cee7514c3aaf..ddfe873b5fcc 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -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);
return 0;