From: Nguyen Dinh Phi phind.uet@gmail.com
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 --- drivers/tty/tty_io.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2294,8 +2294,6 @@ static int tty_fasync(int fd, struct fil * 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) @@ -2311,8 +2309,10 @@ static int tiocsti(struct tty_struct *tt 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; }