USB: cdc-acm: fix write and resume race

Fix race between write() and resume() due to improper locking that could
lead to writes being reordered.

Resume must be done atomically and susp_count be protected by the
write_lock in order to prevent racing with write(). This could otherwise
lead to writes being reordered if write() grabs the write_lock after
susp_count is decremented, but before the delayed urb is submitted.

Fixes: 11ea859d64b6 ("USB: additional power savings for cdc-acm devices
that support remote wakeup")

Cc: <stable@vger.kernel.org>	# v2.6.27
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 14 deletions

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 3bd4226c13dc..e72a657a6177 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1541,27 +1541,20 @@ static int acm_resume(struct usb_interface *intf)
         struct acm *acm = usb_get_intfdata(intf);
         struct acm_wb *wb;
         int rv = 0;
-        int cnt;
 
         spin_lock_irq(&acm->read_lock);
-        acm->susp_count -= 1;
-        cnt = acm->susp_count;
-        spin_unlock_irq(&acm->read_lock);
+        spin_lock(&acm->write_lock);
 
-        if (cnt)
-                return 0;
+        if (--acm->susp_count)
+                goto out;
 
         if (test_bit(ASYNCB_INITIALIZED, &acm->port.flags)) {
-                rv = usb_submit_urb(acm->ctrlurb, GFP_NOIO);
+                rv = usb_submit_urb(acm->ctrlurb, GFP_ATOMIC);
 
-                spin_lock_irq(&acm->write_lock);
                 if (acm->delayed_wb) {
                         wb = acm->delayed_wb;
                         acm->delayed_wb = NULL;
-                        spin_unlock_irq(&acm->write_lock);
                         acm_start_wb(acm, wb);
-                } else {
-                        spin_unlock_irq(&acm->write_lock);
                 }
 
                 /*
@@ -1569,12 +1562,14 @@ static int acm_resume(struct usb_interface *intf)
                  * do the write path at all cost
                  */
                 if (rv < 0)
-                        goto err_out;
+                        goto out;
 
-                rv = acm_submit_read_urbs(acm, GFP_NOIO);
+                rv = acm_submit_read_urbs(acm, GFP_ATOMIC);
         }
+out:
+        spin_unlock(&acm->write_lock);
+        spin_unlock_irq(&acm->read_lock);
 
-err_out:
         return rv;
 }