May 15 2010

[SCSI] aacraid: Eliminate use after free 

Author: Julia Lawall <julia@diku.dk>

The debugging code using the freed structure is moved before the kfree.

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: James Bottomley 

---
 drivers/scsi/aacraid/commctrl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
 
diff --git a/drivers/scsi/aacraid/commctrl.c b/drivers/scsi/aacraid/commctrl.c
index 9c0c911..1a5bf57 100644
--- a/drivers/scsi/aacraid/commctrl.c
+++ b/drivers/scsi/aacraid/commctrl.c
@@ -655,9 +655,9 @@ static int aac_send_raw_srb(struct aac_dev* dev, void __user * arg)
 				/* Does this really need to be GFP_DMA? */
 				p = kmalloc(usg->sg[i].count,GFP_KERNEL|__GFP_DMA);
 				if(!p) {
-					kfree (usg);
-					dprintk((KERN_DEBUG"aacraid: Could not allocate SG buffer - size = %d buffer number %d of %d\n",
+					dprintk((KERN_DEBUG "aacraid: Could not allocate SG buffer - size = %d buffer number %d of %d\n",
 					  usg->sg[i].count,i,usg->count));
+					kfree(usg);
 					rcode = -ENOMEM;
 					goto cleanup;
 				}

qlambert