linux-kernel - [PATCH 3.16 021/294] usb: storage: return on error to avoid a null pointer dereference

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Message-ID: <lsq.1510009382.789906712@decadent.org.uk>
Date:   Mon, 06 Nov 2017 23:03:02 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Colin Ian King" <colin.king@...onical.com>,
        "Alan Stern" <stern@...land.harvard.edu>
Subject: [PATCH 3.16 021/294] usb: storage: return on error to avoid a
 null pointer dereference

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Colin Ian King <colin.king@...onical.com>

commit 446230f52a5bef593554510302465eabab45a372 upstream.

When us->extra is null the driver is not initialized, however, a
later call to osd200_scsi_to_ata is made that dereferences
us->extra, causing a null pointer dereference.  The code
currently detects and reports that the driver is not initialized;
add a return to avoid the subsequent dereference issue in this
check.

Thanks to Alan Stern for pointing out that srb->result needs setting
to DID_ERROR << 16

Detected by CoverityScan, CID#100308 ("Dereference after null check")

Signed-off-by: Colin Ian King <colin.king@...onical.com>
Acked-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/usb/storage/isd200.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/usb/storage/isd200.c
+++ b/drivers/usb/storage/isd200.c
@@ -1522,8 +1522,11 @@ static void isd200_ata_command(struct sc
 
 	/* Make sure driver was initialized */
 
-	if (us->extra == NULL)
+	if (us->extra == NULL) {
 		usb_stor_dbg(us, "ERROR Driver not initialized\n");
+		srb->result = DID_ERROR << 16;
+		return;
+	}
 
 	scsi_set_resid(srb, 0);
 	/* scsi_bufflen might change in protocol translation to ata */