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USB: cdc-acm: fix racy tty buffer accesses

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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: 08dff274ed ("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>
This commit is contained in:
Johan Hovold 2021-09-29 11:09:36 +02:00 committed by Greg Kroah-Hartman
parent 0560c9c552
commit 65a205e611
1 changed files with 5 additions and 0 deletions
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5
drivers/usb/class/cdc-acm.c
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@ -475,11 +475,16 @@ 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);
}