USB: cdc-acm: fix racy tty buffer accesses

commit 65a205e6113506e69a503b61d97efec43fc10fd7 upstream.

A recent change that started reporting break events to the line
discipline caused the tty-buffer insertions to no longer be serialised
by inserting events also from the completion handler for the interrupt
endpoint.

Completion calls for distinct endpoints are not guaranteed to be
serialised. For example, in case a host-controller driver uses
bottom-half completion, the interrupt and bulk-in completion handlers
can end up running in parallel on two CPUs (high-and low-prio tasklets,
respectively) thereby breaking the tty layer's single producer
assumption.

Fix this by holding the read lock also when inserting characters from
the bulk endpoint.

Fixes: 08dff274edda ("cdc-acm: fix BREAK rx code path adding necessary calls")
Cc: stable@vger.kernel.org
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210929090937.7410-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 23df1549eb0d836ed81c0910443707ee91d178f8..768b920e358f8530621aa933be18abff61066816 100644 (file)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -408,11 +408,16 @@ static int acm_submit_read_urbs(struct acm *acm, gfp_t mem_flags)
 
 static void acm_process_read_urb(struct acm *acm, struct urb *urb)
 {
+       unsigned long flags;
+
        if (!urb->actual_length)
                return;
 
+       spin_lock_irqsave(&acm->read_lock, flags);
        tty_insert_flip_string(&acm->port, urb->transfer_buffer,
                        urb->actual_length);
+       spin_unlock_irqrestore(&acm->read_lock, flags);
+
        tty_flip_buffer_push(&acm->port);
 }