ACK: [SRU][Trusty][PATCH 1/1] USB: yurex: fix out-of-bounds uaccess in read handler

[Khaled Elmously]

On 2018-11-09 15:33:25 , Kleber Souza wrote:
> From: Jann Horn <jannh at google.com>
> 
> In general, accessing userspace memory beyond the length of the supplied
> buffer in VFS read/write handlers can lead to both kernel memory corruption
> (via kernel_read()/kernel_write(), which can e.g. be triggered via
> sys_splice()) and privilege escalation inside userspace.
> 
> Fix it by using simple_read_from_buffer() instead of custom logic.
> 
> Fixes: 6bc235a2e24a ("USB: add driver for Meywa-Denki & Kayac YUREX")
> Signed-off-by: Jann Horn <jannh at google.com>
> Cc: stable <stable at vger.kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> 
> CVE-2018-16276
> (backported from commit f1e255d60ae66a9f672ff9a207ee6cd8e33d2679)
> [ klebers: context adjustment ]
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
> ---
>  drivers/usb/misc/yurex.c | 23 ++++++-----------------
>  1 file changed, 6 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
> index b6ab515bfc6c..0a5b1ba47b62 100644
> --- a/drivers/usb/misc/yurex.c
> +++ b/drivers/usb/misc/yurex.c
> @@ -415,8 +415,7 @@ static int yurex_release(struct inode *inode, struct file *file)
>  static ssize_t yurex_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
>  {
>  	struct usb_yurex *dev;
> -	int retval = 0;
> -	int bytes_read = 0;
> +	int len = 0;
>  	char in_buffer[20];
>  	unsigned long flags;
>  
> @@ -424,26 +423,16 @@ static ssize_t yurex_read(struct file *file, char *buffer, size_t count, loff_t
>  
>  	mutex_lock(&dev->io_mutex);
>  	if (!dev->interface) {		/* already disconnected */
> -		retval = -ENODEV;
> -		goto exit;
> +		mutex_unlock(&dev->io_mutex);
> +		return -ENODEV;
>  	}
>  
>  	spin_lock_irqsave(&dev->lock, flags);
> -	bytes_read = snprintf(in_buffer, 20, "%lld\n", dev->bbu);
> +	len = snprintf(in_buffer, 20, "%lld\n", dev->bbu);
>  	spin_unlock_irqrestore(&dev->lock, flags);
> -
> -	if (*ppos < bytes_read) {
> -		if (copy_to_user(buffer, in_buffer + *ppos, bytes_read - *ppos))
> -			retval = -EFAULT;
> -		else {
> -			retval = bytes_read - *ppos;
> -			*ppos += bytes_read;
> -		}
> -	}
> -
> -exit:
>  	mutex_unlock(&dev->io_mutex);
> -	return retval;
> +
> +	return simple_read_from_buffer(buffer, count, ppos, in_buffer, len);
>  }
>  
>  static ssize_t yurex_write(struct file *file, const char *user_buffer, size_t count, loff_t *ppos)

Acked-by: Khalid Elmously <khalid.elmously at canonical.com>