[PATCH] usb: gadget: pch_udc: fix use after free

[PATCH] usb: gadget: pch_udc: fix use after free

[Pan Bian]

The next field of the DMA descriptor is written after releasing the
descriptor, which may result in a use-after-free issue. Set the value of
the field before it is released to fix the bug.

Signed-off-by: Pan Bian <bianpan2016@163.com>
---
 drivers/usb/gadget/udc/pch_udc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/udc/pch_udc.c b/drivers/usb/gadget/udc/pch_udc.c
index 265dab2bbfac..c5b8ec908aab 100644
--- a/drivers/usb/gadget/udc/pch_udc.c
+++ b/drivers/usb/gadget/udc/pch_udc.c
@@ -1518,8 +1518,8 @@ static void pch_udc_free_dma_chain(struct pch_udc_dev *dev,
 		/* do not free first desc., will be done by free for request */
 		td = phys_to_virt(addr);
 		addr2 = (dma_addr_t)td->next;
-		dma_pool_free(dev->data_requests, td, addr);
 		td->next = 0x00;
+		dma_pool_free(dev->data_requests, td, addr);
 		addr = addr2;
 	}
 	req->chain_len = 1;
-- 
2.7.4

Re: [PATCH] usb: gadget: pch_udc: fix use after free

[Andy Shevchenko]

On Wed, Nov 6, 2019 at 10:41 AM Pan Bian <bianpan2016@163.com> wrote:
>
> The next field of the DMA descriptor is written after releasing the
> descriptor, which may result in a use-after-free issue. Set the value of
> the field before it is released to fix the bug.
>

Had you chance to read the discussion [1]?
I Cc to Gustavo to hear from him about destiny of the change.

[1]: http://lkml.iu.edu/hypermail/linux/kernel/1702.1/00843.html

> Signed-off-by: Pan Bian <bianpan2016@163.com>
> ---
>  drivers/usb/gadget/udc/pch_udc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/usb/gadget/udc/pch_udc.c b/drivers/usb/gadget/udc/pch_udc.c
> index 265dab2bbfac..c5b8ec908aab 100644
> --- a/drivers/usb/gadget/udc/pch_udc.c
> +++ b/drivers/usb/gadget/udc/pch_udc.c
> @@ -1518,8 +1518,8 @@ static void pch_udc_free_dma_chain(struct pch_udc_dev *dev,
>                 /* do not free first desc., will be done by free for request */
>                 td = phys_to_virt(addr);
>                 addr2 = (dma_addr_t)td->next;
> -               dma_pool_free(dev->data_requests, td, addr);
>                 td->next = 0x00;
> +               dma_pool_free(dev->data_requests, td, addr);
>                 addr = addr2;
>         }
>         req->chain_len = 1;
> --
> 2.7.4
>


-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] usb: gadget: pch_udc: fix use after free

[Gustavo A. R. Silva]

On 11/6/19 02:54, Andy Shevchenko wrote:
> On Wed, Nov 6, 2019 at 10:41 AM Pan Bian <bianpan2016@163.com> wrote:
>>
>> The next field of the DMA descriptor is written after releasing the
>> descriptor, which may result in a use-after-free issue. Set the value of
>> the field before it is released to fix the bug.
>>
> 
> Had you chance to read the discussion [1]?
> I Cc to Gustavo to hear from him about destiny of the change.
> 

Wow, thanks for reminding me about this thread, Andy.
I had totally forgotten about this for more than two years... :|

Here is the final version:

https://lore.kernel.org/lkml/20191106202821.GA20347@embeddedor/

Thanks
--
Gustavo