There is a race in pty_write(). pty_write() can be called in parallel with e.g. ioctl(TIOCSTI) or ioctl(TCXONC) which also inserts chars to the buffer. Provided, tty_flip_buffer_push() in pty_write() is called outside the lock, it can commit inconsistent tail. This can lead to out of bounds writes and other issues. See the Link below. To fix this, we have to introduce a new helper called tty_insert_flip_string_and_push_buffer(). It does both tty_insert_flip_string() and tty_flip_buffer_commit() under the port lock. It also calls queue_work(), but outside the lock. See 71a174b39f10 (pty: do tty_flip_buffer_push without port->lock in pty_write) for the reasons. Keep the helper internal-only (in drivers' tty.h). It is not intended to be used widely. Link: https://seclists.org/oss-sec/2022/q2/155 Fixes: 71a174b39f10 (pty: do tty_flip_buffer_push without port->lock in pty_write) Cc: 一只狗 <chennbnbnb@xxxxxxxxx> Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx> Suggested-by: Hillf Danton <hdanton@xxxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- drivers/tty/pty.c | 14 ++------------ drivers/tty/tty.h | 3 +++ drivers/tty/tty_buffer.c | 31 +++++++++++++++++++++++++++++++ 3 files changed, 36 insertions(+), 12 deletions(-) diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index 74bfabe5b453..752dab3356d7 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -111,21 +111,11 @@ static void pty_unthrottle(struct tty_struct *tty) static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c) { struct tty_struct *to = tty->link; - unsigned long flags; - if (tty->flow.stopped) + if (tty->flow.stopped || !c) return 0; - if (c > 0) { - spin_lock_irqsave(&to->port->lock, flags); - /* Stuff the data into the input queue of the other end */ - c = tty_insert_flip_string(to->port, buf, c); - spin_unlock_irqrestore(&to->port->lock, flags); - /* And shovel */ - if (c) - tty_flip_buffer_push(to->port); - } - return c; + return tty_insert_flip_string_and_push_buffer(to->port, buf, c); } /** diff --git a/drivers/tty/tty.h b/drivers/tty/tty.h index b710c5ef89ab..f310a8274df1 100644 --- a/drivers/tty/tty.h +++ b/drivers/tty/tty.h @@ -111,4 +111,7 @@ static inline void tty_audit_tiocsti(struct tty_struct *tty, char ch) ssize_t redirected_tty_write(struct kiocb *, struct iov_iter *); +int tty_insert_flip_string_and_push_buffer(struct tty_port *port, + const unsigned char *chars, size_t cnt); + #endif diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index ea630ceda009..9fdecc795b6b 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -601,6 +601,37 @@ void tty_flip_buffer_push(struct tty_port *port) } EXPORT_SYMBOL(tty_flip_buffer_push); +/** + * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and + * push + * @port: tty port + * @chars: characters + * @size: size + * + * The function combines tty_insert_flip_string() and tty_flip_buffer_push() + * with the exception of properly holding the @port->lock. + * + * To be used only internally (by pty currently). + * + * Returns: the number added. + */ +int tty_insert_flip_string_and_push_buffer(struct tty_port *port, + const unsigned char *chars, size_t size) +{ + struct tty_bufhead *buf = &port->buf; + unsigned long flags; + + spin_lock_irqsave(&port->lock, flags); + size = tty_insert_flip_string(port, chars, size); + if (size) + tty_flip_buffer_commit(buf->tail); + spin_unlock_irqrestore(&port->lock, flags); + + queue_work(system_unbound_wq, &buf->work); + + return size; +} + /** * tty_buffer_init - prepare a tty buffer structure * @port: tty port to initialise -- 2.36.1
