May 15 2010

HID: picolcd: Eliminate use after free 

Author: 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/)

// 
@free@
expression E;
position p;
@@
kfree@p(E)

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

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

Signed-off-by: Julia Lawall 
Signed-off-by: Jiri Kosina 

---
 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]);

qlambert