USB: gadgetfs: Fix crash caused by inadequate synchronization

commit 520b72fc64debf8a86c3853b8e486aa5982188f0 upstream.

The gadgetfs driver (drivers/usb/gadget/legacy/inode.c) was written
before the UDC and composite frameworks were adopted; it is a legacy
driver.  As such, it expects that once bound to a UDC controller, it
will not be unbound until it unregisters itself.

However, the UDC framework does unbind function drivers while they are
still registered.  When this happens, it can cause the gadgetfs driver
to misbehave or crash.  For example, userspace can cause a crash by
opening the device file and doing an ioctl call before setting up a
configuration (found by Andrey Konovalov using the syzkaller fuzzer).

This patch adds checks and synchronization to prevent these bad
behaviors.  It adds a udc_usage counter that the driver increments at
times when it is using a gadget interface without holding the private
spinlock.  The unbind routine waits for this counter to go to 0 before
returning, thereby ensuring that the UDC is no longer in use.

The patch also adds a check in the dev_ioctl() routine to make sure
the driver is bound to a UDC before dereferencing the gadget pointer,
and it makes destroy_ep_files() synchronize with the endpoint I/O
routines, to prevent the user from accessing an endpoint data
structure after it has been removed.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2:
 - Expand locked section in ep0_write() to match upstream
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/usb/gadget/inode.c b/drivers/usb/gadget/inode.c
index b32e386..10855e2 100644 (file)
--- a/drivers/usb/gadget/inode.c
+++ b/drivers/usb/gadget/inode.c
@@ -24,7 +24,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/poll.h>
-
+#include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/moduleparam.h>
 
@@ -112,6 +112,7 @@ enum ep0_state {
 struct dev_data {
        spinlock_t                      lock;
        atomic_t                        count;
+       int                             udc_usage;
        enum ep0_state                  state;          /* P: lock */
        struct usb_gadgetfs_event       event [N_EVENT];
        unsigned                        ev_next;
@@ -608,9 +609,9 @@ static void ep_aio_complete(struct usb_ep *ep, struct usb_request *req)
                priv->actual = req->actual;
                kick_iocb(iocb);
        }
-       spin_unlock(&epdata->dev->lock);
 
        usb_ep_free_request(ep, req);
+       spin_unlock(&epdata->dev->lock);
        put_ep(epdata);
 }
 
@@ -1010,9 +1011,11 @@ ep0_read (struct file *fd, char __user *buf, size_t len, loff_t *ptr)
                        struct usb_request      *req = dev->req;
 
                        if ((retval = setup_req (ep, req, 0)) == 0) {
+                               ++dev->udc_usage;
                                spin_unlock_irq (&dev->lock);
                                retval = usb_ep_queue (ep, req, GFP_KERNEL);
                                spin_lock_irq (&dev->lock);
+                               --dev->udc_usage;
                        }
                        dev->state = STATE_DEV_CONNECTED;
 
@@ -1207,6 +1210,7 @@ ep0_write (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
                        retval = setup_req (dev->gadget->ep0, dev->req, len);
                        if (retval == 0) {
                                dev->state = STATE_DEV_CONNECTED;
+                               ++dev->udc_usage;
                                spin_unlock_irq (&dev->lock);
                                if (copy_from_user (dev->req->buf, buf, len))
                                        retval = -EFAULT;
@@ -1217,12 +1221,13 @@ ep0_write (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
                                                dev->gadget->ep0, dev->req,
                                                GFP_KERNEL);
                                }
+                               spin_lock_irq(&dev->lock);
+                               --dev->udc_usage;
                                if (retval < 0) {
-                                       spin_lock_irq (&dev->lock);
                                        clean_req (dev->gadget->ep0, dev->req);
-                                       spin_unlock_irq (&dev->lock);
                                } else
                                        retval = len;
+                               spin_unlock_irq(&dev->lock);
 
                                return retval;
                        }
@@ -1314,9 +1319,21 @@ static long dev_ioctl (struct file *fd, unsigned code, unsigned long value)
        struct usb_gadget       *gadget = dev->gadget;
        long ret = -ENOTTY;
 
-       if (gadget->ops->ioctl)
+       spin_lock_irq(&dev->lock);
+       if (dev->state == STATE_DEV_OPENED ||
+                       dev->state == STATE_DEV_UNBOUND) {
+               /* Not bound to a UDC */
+       } else if (gadget->ops->ioctl) {
+               ++dev->udc_usage;
+               spin_unlock_irq(&dev->lock);
+
                ret = gadget->ops->ioctl (gadget, code, value);
 
+               spin_lock_irq(&dev->lock);
+               --dev->udc_usage;
+       }
+       spin_unlock_irq(&dev->lock);
+
        return ret;
 }
 
@@ -1551,10 +1568,12 @@ delegate:
                                if (value < 0)
                                        break;
 
+                               ++dev->udc_usage;
                                spin_unlock (&dev->lock);
                                value = usb_ep_queue (gadget->ep0, dev->req,
                                                        GFP_KERNEL);
                                spin_lock (&dev->lock);
+                               --dev->udc_usage;
                                if (value < 0) {
                                        clean_req (gadget->ep0, dev->req);
                                        break;
@@ -1578,8 +1597,12 @@ delegate:
                req->length = value;
                req->zero = value < w_length;
 
+               ++dev->udc_usage;
                spin_unlock (&dev->lock);
                value = usb_ep_queue (gadget->ep0, req, GFP_KERNEL);
+               spin_lock(&dev->lock);
+               --dev->udc_usage;
+               spin_unlock(&dev->lock);
                if (value < 0) {
                        DBG (dev, "ep_queue --> %d\n", value);
                        req->status = 0;
@@ -1609,21 +1632,24 @@ restart:
                /* break link to FS */
                ep = list_entry (entry, struct ep_data, epfiles);
                list_del_init (&ep->epfiles);
+               spin_unlock_irq (&dev->lock);
+
                dentry = ep->dentry;
                ep->dentry = NULL;
                parent = dentry->d_parent->d_inode;
 
                /* break link to controller */
+               mutex_lock(&ep->lock);
                if (ep->state == STATE_EP_ENABLED)
                        (void) usb_ep_disable (ep->ep);
                ep->state = STATE_EP_UNBOUND;
                usb_ep_free_request (ep->ep, ep->req);
                ep->ep = NULL;
+               mutex_unlock(&ep->lock);
+
                wake_up (&ep->wait);
                put_ep (ep);
 
-               spin_unlock_irq (&dev->lock);
-
                /* break link to dcache */
                mutex_lock (&parent->i_mutex);
                d_delete (dentry);
@@ -1697,6 +1723,11 @@ gadgetfs_unbind (struct usb_gadget *gadget)
 
        spin_lock_irq (&dev->lock);
        dev->state = STATE_DEV_UNBOUND;
+       while (dev->udc_usage > 0) {
+               spin_unlock_irq(&dev->lock);
+               usleep_range(1000, 2000);
+               spin_lock_irq(&dev->lock);
+       }
        spin_unlock_irq (&dev->lock);
 
        destroy_ep_files (dev);