From 08afa87f58d83dfe040572ed591b47e8cb9e225c Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Thu, 7 Jul 2022 10:25:58 +0200 Subject: [PATCH] tty: use new tty_insert_flip_string_and_push_buffer() in pty_write() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit commit a501ab75e7624d133a5a3c7ec010687c8b961d23 upstream. 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 Cc: Dan Carpenter Suggested-by: Hillf Danton Signed-off-by: Jiri Slaby Link: https://lore.kernel.org/r/20220707082558.9250-2-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman --- drivers/tty/pty.c | 14 ++------------ drivers/tty/tty_buffer.c | 31 +++++++++++++++++++++++++++++++ include/linux/tty_flip.h | 3 +++ 3 files changed, 36 insertions(+), 12 deletions(-) diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index 23368cec7ee8..16498f5fba64 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->stopped) + if (tty->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_buffer.c b/drivers/tty/tty_buffer.c index bf8d4160411c..5bbc2e010b48 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -552,6 +552,37 @@ 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 diff --git a/include/linux/tty_flip.h b/include/linux/tty_flip.h index e183f74b19a0..c326bfdb5ec2 100644 --- a/include/linux/tty_flip.h +++ b/include/linux/tty_flip.h @@ -39,4 +39,7 @@ static inline int tty_insert_flip_string(struct tty_port *port, extern void tty_buffer_lock_exclusive(struct tty_port *port); extern void tty_buffer_unlock_exclusive(struct tty_port *port); +int tty_insert_flip_string_and_push_buffer(struct tty_port *port, + const unsigned char *chars, size_t cnt); + #endif /* _LINUX_TTY_FLIP_H */