linux-kernel - [19/27] SCSI: scsi_lib: fix potential NULL dereference

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Message-Id: <20111207165602.002157755@clark.kroah.org>
Date:	Wed, 07 Dec 2011 08:54:52 -0800
From:	Greg KH <gregkh@...e.de>
To:	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Cc:	<torvalds@...ux-foundation.org>, <akpm@...ux-foundation.org>,
	<alan@...rguk.ukuu.org.uk>, Jiri Slaby <jirislaby@...il.com>,
	James Bottomley <James.Bottomley@...e.de>
Subject: [19/27] SCSI: scsi_lib: fix potential NULL dereference

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Slaby <jirislaby@...il.com>

commit 03b147083a2f9a2a3fbbd2505fa88ffa3c6ab194 upstream.

Stanse found a potential NULL dereference in scsi_kill_request.

Instead of triggering BUG() in 'if (unlikely(cmd == NULL))' branch,
the kernel will Oops earlier on cmd dereference.

Move the dereferences after the if.

Signed-off-by: Jiri Slaby <jirislaby@...il.com>
Signed-off-by: James Bottomley <James.Bottomley@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/scsi/scsi_lib.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1370,9 +1370,9 @@ static int scsi_lld_busy(struct request_
 static void scsi_kill_request(struct request *req, struct request_queue *q)
 {
 	struct scsi_cmnd *cmd = req->special;
-	struct scsi_device *sdev = cmd->device;
-	struct scsi_target *starget = scsi_target(sdev);
-	struct Scsi_Host *shost = sdev->host;
+	struct scsi_device *sdev;
+	struct scsi_target *starget;
+	struct Scsi_Host *shost;
 
 	blk_start_request(req);
 
@@ -1382,6 +1382,9 @@ static void scsi_kill_request(struct req
 		BUG();
 	}
 
+	sdev = cmd->device;
+	starget = scsi_target(sdev);
+	shost = sdev->host;
 	scsi_init_cmd_errh(cmd);
 	cmd->result = DID_NO_CONNECT << 16;
 	atomic_inc(&cmd->device->iorequest_cnt);


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