cdc-acm: fix crash if flushed with nothing buffered

Under some circumstances acm_tty_flush_chars() is called
with no buffer to flush. We simply need to do nothing.

Signed-off-by: Oliver Neukum <ONeukum@suse.com>
Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 83fd30b0577c..a6c4a1b895bd 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -744,11 +744,15 @@ static void acm_tty_flush_chars(struct tty_struct *tty)
         int err;
         unsigned long flags;
 
+        if (!cur) /* nothing to do */
+                return;
+
         acm->putbuffer = NULL;
         err = usb_autopm_get_interface_async(acm->control);
         spin_lock_irqsave(&acm->write_lock, flags);
         if (err < 0) {
                 cur->use = 0;
+                acm->putbuffer = cur;
                 goto out;
         }