[PATCH] usb: gadget: use after free in dev_config

[PATCH] usb: gadget: use after free in dev_config

[Hangyu Hua]

There are two bugs:
dev->buf does not need to be released if it already exists before
executing dev_config.
dev->config and dev->hs_config and dev->dev need to be cleaned if
dev_config fails to avoid UAF.

Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
---
 drivers/usb/gadget/legacy/inode.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 3b58f4fc0a80..2ea02887025b 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -1826,8 +1826,9 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 	spin_lock_irq (&dev->lock);
 	value = -EINVAL;
 	if (dev->buf) {
+		spin_unlock_irq(&dev->lock);
 		kfree(kbuf);
-		goto fail;
+		return value;
 	}
 	dev->buf = kbuf;
 
@@ -1835,8 +1836,10 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 	dev->config = (void *) kbuf;
 	total = le16_to_cpu(dev->config->wTotalLength);
 	if (!is_valid_config(dev->config, total) ||
-			total > length - USB_DT_DEVICE_SIZE)
+			total > length - USB_DT_DEVICE_SIZE) {
+		dev->config = NULL;
 		goto fail;
+	}
 	kbuf += total;
 	length -= total;
 
@@ -1845,8 +1848,11 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 		dev->hs_config = (void *) kbuf;
 		total = le16_to_cpu(dev->hs_config->wTotalLength);
 		if (!is_valid_config(dev->hs_config, total) ||
-				total > length - USB_DT_DEVICE_SIZE)
+				total > length - USB_DT_DEVICE_SIZE) {
+			dev->config = NULL;
+			dev->hs_config = NULL;
 			goto fail;
+		}
 		kbuf += total;
 		length -= total;
 	} else {
@@ -1856,13 +1862,20 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 	/* could support multiple configs, using another encoding! */
 
 	/* device descriptor (tweaked for paranoia) */
-	if (length != USB_DT_DEVICE_SIZE)
+	if (length != USB_DT_DEVICE_SIZE) {
+		dev->config = NULL;
+		dev->hs_config = NULL;
 		goto fail;
+	}
 	dev->dev = (void *)kbuf;
 	if (dev->dev->bLength != USB_DT_DEVICE_SIZE
 			|| dev->dev->bDescriptorType != USB_DT_DEVICE
-			|| dev->dev->bNumConfigurations != 1)
+			|| dev->dev->bNumConfigurations != 1) {
+		dev->config = NULL;
+		dev->hs_config = NULL;
+		dev->dev = NULL;
 		goto fail;
+	}
 	dev->dev->bcdUSB = cpu_to_le16 (0x0200);
 
 	/* triggers gadgetfs_bind(); then we can enumerate. */
-- 
2.25.1

Re: [PATCH] usb: gadget: use after free in dev_config

[Alan Stern]

On Tue, Dec 28, 2021 at 05:21:26PM +0800, Hangyu Hua wrote:
> There are two bugs:

You should break this up into two separate patches, one for each bug.

> dev->buf does not need to be released if it already exists before
> executing dev_config.

That's right.  The call to dev_config should fail without changing any 
of the stored values.

> dev->config and dev->hs_config and dev->dev need to be cleaned if
> dev_config fails to avoid UAF.

Do they really need to be cleared?  I think if dev_config fails then 
those pointers never get used, so it doesn't matter what they contain.

Of course, clearing them doesn't hurt, but it would be best to clear 
all of them in the "fail:" part of the routine.  And then you would 
want to change the pathway where usb_gadget_probe_driver fails, to make 
it go to "fail:" also.

Alan Stern

Re: [PATCH] usb: gadget: use after free in dev_config

[Hangyu Hua]

Thank for your suggesions. I will break this up into two separate 
patches later. And i think it's necessary to clear up dev->config and
dev->hs_config and dev->dev. For example, dev->hs_config is used in
ep0_read() which may lead a UAF.

Thanks.

On 2021/12/30 上午5:11, Alan Stern wrote:
> On Tue, Dec 28, 2021 at 05:21:26PM +0800, Hangyu Hua wrote:
>> There are two bugs:
> 
> You should break this up into two separate patches, one for each bug.
> 
>> dev->buf does not need to be released if it already exists before
>> executing dev_config.
> 
> That's right.  The call to dev_config should fail without changing any
> of the stored values.
> 
>> dev->config and dev->hs_config and dev->dev need to be cleaned if
>> dev_config fails to avoid UAF.
> 
> Do they really need to be cleared?  I think if dev_config fails then
> those pointers never get used, so it doesn't matter what they contain.
> 
> Of course, clearing them doesn't hurt, but it would be best to clear
> all of them in the "fail:" part of the routine.  And then you would
> want to change the pathway where usb_gadget_probe_driver fails, to make
> it go to "fail:" also.
> 
> Alan Stern
>