[PATCH v4 0/2] usb: gadget: use after free in dev_config

[PATCH v4 0/2] 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.

v2:
1. break one patch up into two separate patches.
2. use "fail:" to clear all members.

v3:
fix a mistake in [PATCH v3 2/2]

v4:
avoid multiple unnecessary statement labels in [PATCH v4 2/2]

Hangyu Hua (2):
  usb: gadget: don't release an existing dev->buf
  usb: gadget: clear related members when goto fail

 drivers/usb/gadget/legacy/inode.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

-- 
2.25.1

[PATCH v4 1/2] usb: gadget: don't release an existing dev->buf

[Hangyu Hua]

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

Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
---
 drivers/usb/gadget/legacy/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 3b58f4fc0a80..eaad03c0252f 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;
 
-- 
2.25.1

[PATCH v4 2/2] usb: gadget: clear related members when goto fail

[Hangyu Hua]

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 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index eaad03c0252f..25c8809e0a38 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -1875,8 +1875,8 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 
 	value = usb_gadget_probe_driver(&gadgetfs_driver);
 	if (value != 0) {
-		kfree (dev->buf);
-		dev->buf = NULL;
+		spin_lock_irq(&dev->lock);
+		goto fail;
 	} else {
 		/* at this point "good" hardware has for the first time
 		 * let the USB the host see us.  alternatively, if users
@@ -1893,6 +1893,9 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 	return value;
 
 fail:
+	dev->config = NULL;
+	dev->hs_config = NULL;
+	dev->dev = NULL;
 	spin_unlock_irq (&dev->lock);
 	pr_debug ("%s: %s fail %zd, %p\n", shortname, __func__, value, dev);
 	kfree (dev->buf);
-- 
2.25.1

Re: [PATCH v4 1/2] usb: gadget: don't release an existing dev->buf

[Alan Stern]

On Sat, Jan 01, 2022 at 01:21:37AM +0800, Hangyu Hua wrote:
> dev->buf does not need to be released if it already exists before
> executing dev_config.
> 
> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
> ---

Acked-by: Alan Stern <stern@rowland.harvard.edu>

>  drivers/usb/gadget/legacy/inode.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
> index 3b58f4fc0a80..eaad03c0252f 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;
>  
> -- 
> 2.25.1
> 

Re: [PATCH v4 2/2] usb: gadget: clear related members when goto fail

[Alan Stern]

On Sat, Jan 01, 2022 at 01:21:38AM +0800, Hangyu Hua wrote:
> 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>
> ---

Acked-by: Alan Stern <stern@rowland.harvard.edu>

>  drivers/usb/gadget/legacy/inode.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
> index eaad03c0252f..25c8809e0a38 100644
> --- a/drivers/usb/gadget/legacy/inode.c
> +++ b/drivers/usb/gadget/legacy/inode.c
> @@ -1875,8 +1875,8 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
>  
>  	value = usb_gadget_probe_driver(&gadgetfs_driver);
>  	if (value != 0) {
> -		kfree (dev->buf);
> -		dev->buf = NULL;
> +		spin_lock_irq(&dev->lock);
> +		goto fail;
>  	} else {
>  		/* at this point "good" hardware has for the first time
>  		 * let the USB the host see us.  alternatively, if users
> @@ -1893,6 +1893,9 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
>  	return value;
>  
>  fail:
> +	dev->config = NULL;
> +	dev->hs_config = NULL;
> +	dev->dev = NULL;
>  	spin_unlock_irq (&dev->lock);
>  	pr_debug ("%s: %s fail %zd, %p\n", shortname, __func__, value, dev);
>  	kfree (dev->buf);
> -- 
> 2.25.1
>