linux-kernel - [PATCH] drivers/usb/host: Eliminate NULL dereference

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Date:	Thu, 27 May 2010 18:10:08 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	David Vrabel <david.vrabel@....com>,
	Greg Kroah-Hartman <gregkh@...e.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH] drivers/usb/host: Eliminate NULL dereference

From: Julia Lawall <julia@...u.dk>

The test above allows std to be NULL, so check that std is not NULL before
doing the dereference.

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

// <smpl>
@r exists@
expression E,E1;
identifier f;
statement S1,S2,S3;
@@

if ((E == NULL && ...) || ...)
{
  ... when != if (...) S1 else S2
      when != E = E1
* E->f
  ... when any
}
else S3
// </smpl>

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

---
diff --git a/drivers/usb/host/whci/qset.c b/drivers/usb/host/whci/qset.c
index ab5a14f..dc0ab83 100644
--- a/drivers/usb/host/whci/qset.c
+++ b/drivers/usb/host/whci/qset.c
@@ -475,7 +475,7 @@ static int qset_add_urb_sg(struct whc *whc, struct whc_qset *qset, struct urb *u
 			    || (prev_end & (WHCI_PAGE_SIZE-1))
 			    || (dma_addr & (WHCI_PAGE_SIZE-1))
 			    || std->len + WHCI_PAGE_SIZE > QTD_MAX_XFER_SIZE) {
-				if (std->len % qset->max_packet != 0)
+				if (std && std->len % qset->max_packet != 0)
 					return -EINVAL;
 				std = qset_new_std(whc, qset, urb, mem_flags);
 				if (std == NULL) {
--
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