[PATCH 3/4] drivers/hid: Eliminate use after free

[PATCH 3/4] drivers/hid: Eliminate use after free

[Julia Lawall]

From: Julia Lawall <julia@diku.dk>

The skip label frees resp, which has not been allocated at the point of
this goto and then does a break, based on the fact that err is non-zero.
This is replaced by a break directly.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@free@
expression E;
position p;
@@
kfree@p(E)

@@
expression free.E, subE<=free.E, E1;
position free.p;
@@

  kfree@p(E)
  ...
(
  subE = E1
|
* E
)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>

---
 drivers/hid/hid-picolcd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hid/hid-picolcd.c b/drivers/hid/hid-picolcd.c
index 95253b3..7aabf65 100644
--- a/drivers/hid/hid-picolcd.c
+++ b/drivers/hid/hid-picolcd.c
@@ -1616,7 +1616,7 @@ static ssize_t _picolcd_flash_write(struct picolcd_data *data, int report_id,
 		raw_data[len_off] = s > 32 ? 32 : s;
 		if (copy_from_user(raw_data+len_off+1, u, raw_data[len_off])) {
 			err = -EFAULT;
-			goto skip;
+			break;
 		}
 		resp = picolcd_send_and_wait(data->hdev, report_id, raw_data,
 				len_off+1+raw_data[len_off]);

Re: [PATCH 3/4] drivers/hid: Eliminate use after free

[Jiri Kosina]

On Sat, 15 May 2010, Julia Lawall wrote:

> From: Julia Lawall <julia@diku.dk>
> 
> The skip label frees resp, which has not been allocated at the point of
> this goto and then does a break, based on the fact that err is non-zero.
> This is replaced by a break directly.
> 
> A simplified version of the semantic match that finds this problem is as
> follows: (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @free@
> expression E;
> position p;
> @@
> kfree@p(E)
> 
> @@
> expression free.E, subE<=free.E, E1;
> position free.p;
> @@
> 
>   kfree@p(E)
>   ...
> (
>   subE = E1
> |
> * E
> )
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@diku.dk>
> 
> ---
>  drivers/hid/hid-picolcd.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/hid-picolcd.c b/drivers/hid/hid-picolcd.c
> index 95253b3..7aabf65 100644
> --- a/drivers/hid/hid-picolcd.c
> +++ b/drivers/hid/hid-picolcd.c
> @@ -1616,7 +1616,7 @@ static ssize_t _picolcd_flash_write(struct picolcd_data *data, int report_id,
>  		raw_data[len_off] = s > 32 ? 32 : s;
>  		if (copy_from_user(raw_data+len_off+1, u, raw_data[len_off])) {
>  			err = -EFAULT;
> -			goto skip;
> +			break;
>  		}
>  		resp = picolcd_send_and_wait(data->hdev, report_id, raw_data,
>  				len_off+1+raw_data[len_off]);

Good catch, applied. Thanks,

-- 
Jiri Kosina
SUSE Labs, Novell Inc.