From: Johan Hovold Date: Wed, 29 Sep 2021 09:09:36 +0000 (+0200) Subject: USB: cdc-acm: fix racy tty buffer accesses X-Git-Tag: v4.4.289~18 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2c1ac7ecf93fad5870e8a15efbf166ed2a7c25c2;p=thirdparty%2Fkernel%2Fstable.git 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 Signed-off-by: Johan Hovold Link: https://lore.kernel.org/r/20210929090937.7410-2-johan@kernel.org Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 44184cc6585e6..aa4028c551e1f 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -407,11 +407,16 @@ 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); }