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SubjectRe: usb/gadget: null-ptr-deref in dev_ioctl
On Mon, 11 Sep 2017, Andrey Konovalov wrote:

> Hi!
>
> It seems that gadget->ops can be NULL so it probably needs to be
> checked as well as gadget->ops->ioctl in dev_ioctl() in
> drivers/usb/gadget/legacy/inode.c.

Actually, I suspect the problem is that gadget is NULL, not
gadget->ops.

> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 1 PID: 5214 Comm: syz-executor Not tainted 4.13.0+ #94
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff88006ac0e800 task.stack: ffff88006af60000
> ! handling hub events now: start
> RIP: 0010:dev_ioctl+0x117/0x280 drivers/usb/gadget/legacy/inode.c:1323

Can you test the patch below? I haven't tried it myself yet, but I
think it will fix the problem you found.

Alan Stern



Index: usb-4.x/drivers/usb/gadget/legacy/inode.c
===================================================================
--- usb-4.x.orig/drivers/usb/gadget/legacy/inode.c
+++ usb-4.x/drivers/usb/gadget/legacy/inode.c
@@ -28,7 +28,7 @@
#include <linux/aio.h>
#include <linux/uio.h>
#include <linux/refcount.h>
-
+#include <linux/delay.h>
#include <linux/device.h>
#include <linux/moduleparam.h>

@@ -116,6 +116,7 @@ enum ep0_state {
struct dev_data {
spinlock_t lock;
refcount_t count;
+ int udc_usage;
enum ep0_state state; /* P: lock */
struct usb_gadgetfs_event event [N_EVENT];
unsigned ev_next;
@@ -513,9 +514,9 @@ static void ep_aio_complete(struct usb_e
INIT_WORK(&priv->work, ep_user_copy_worker);
schedule_work(&priv->work);
}
- spin_unlock(&epdata->dev->lock);

usb_ep_free_request(ep, req);
+ spin_unlock(&epdata->dev->lock);
put_ep(epdata);
}

@@ -939,9 +940,11 @@ ep0_read (struct file *fd, char __user *
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;

@@ -1131,6 +1134,7 @@ ep0_write (struct file *fd, const char _
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;
@@ -1142,6 +1146,7 @@ ep0_write (struct file *fd, const char _
GFP_KERNEL);
}
spin_lock_irq(&dev->lock);
+ --dev->udc_usage;
if (retval < 0) {
clean_req (dev->gadget->ep0, dev->req);
} else
@@ -1243,9 +1248,21 @@ static long dev_ioctl (struct file *fd,
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;
}

@@ -1463,10 +1480,12 @@ 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;
@@ -1490,8 +1509,12 @@ 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;
@@ -1518,21 +1541,24 @@ static void destroy_ep_files (struct dev
/* break link to FS */
ep = list_first_entry (&dev->epfiles, struct ep_data, epfiles);
list_del_init (&ep->epfiles);
+ spin_unlock_irq (&dev->lock);
+
dentry = ep->dentry;
ep->dentry = NULL;
parent = d_inode(dentry->d_parent);

/* 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 */
inode_lock(parent);
d_delete (dentry);
@@ -1603,6 +1629,11 @@ gadgetfs_unbind (struct usb_gadget *gadg

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);
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