Re: [PATCH v2] usb: gadget: configfs: Fix use-after-free issue with udc_name

[Macpaul Lin]

On Sat, 2020-07-18 at 10:45 +0800, Macpaul Lin wrote:
> From: Eddie Hung <eddie.hung@xxxxxxxxxxxx>
> There is a use-after-free issue, if access udc_name
> in function gadget_dev_desc_UDC_store after another context
> free udc_name in function unregister_gadget.
> 
> Context 1:
> gadget_dev_desc_UDC_store()->unregister_gadget()->
> free udc_name->set udc_name to NULL
> 
> Context 2:
> gadget_dev_desc_UDC_show()-> access udc_name
> 
> Call trace:
> dump_backtrace+0x0/0x340
> show_stack+0x14/0x1c
> dump_stack+0xe4/0x134
> print_address_description+0x78/0x478
> __kasan_report+0x270/0x2ec
> kasan_report+0x10/0x18
> __asan_report_load1_noabort+0x18/0x20
> string+0xf4/0x138
> vsnprintf+0x428/0x14d0
> sprintf+0xe4/0x12c
> gadget_dev_desc_UDC_show+0x54/0x64
> configfs_read_file+0x210/0x3a0
> __vfs_read+0xf0/0x49c
> vfs_read+0x130/0x2b4
> SyS_read+0x114/0x208
> el0_svc_naked+0x34/0x38
> 
> Add mutex_lock to protect this kind of scenario.
> 
> Signed-off-by: Eddie Hung <eddie.hung@xxxxxxxxxxxx>
> Signed-off-by: Macpaul Lin <macpaul.lin@xxxxxxxxxxxx>
> Reviewed-by: Peter Chen <peter.chen@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> Changes for v2:
>   - Fix typo %s/contex/context, Thanks Peter.
> 
>  drivers/usb/gadget/configfs.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> index 9dc06a4e1b30..21110b2865b9 100644
> --- a/drivers/usb/gadget/configfs.c
> +++ b/drivers/usb/gadget/configfs.c
> @@ -221,9 +221,16 @@ static ssize_t gadget_dev_desc_bcdUSB_store(struct config_item *item,
>  
>  static ssize_t gadget_dev_desc_UDC_show(struct config_item *item, char *page)
>  {
> -	char *udc_name = to_gadget_info(item)->composite.gadget_driver.udc_name;
> +	struct gadget_info *gi = to_gadget_info(item);
> +	char *udc_name;
> +	int ret;
> +
> +	mutex_lock(&gi->lock);
> +	udc_name = gi->composite.gadget_driver.udc_name;
> +	ret = sprintf(page, "%s\n", udc_name ?: "");
> +	mutex_unlock(&gi->lock);
>  
> -	return sprintf(page, "%s\n", udc_name ?: "");
> +	return ret;
>  }
>  
>  static int unregister_gadget(struct gadget_info *gi)

Just want to remind we have a fix here for usb/gadget/configfs.c.
If the patch need to be further revised, please let us know.

Thanks!
Macpaul Lin