netdev - [PATCH net-next] can: sja1000: fix use after free in ems_pcmcia_add

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Date:   Mon, 22 Nov 2021 10:56:14 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Wolfgang Grandegger <wg@...ndegger.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Leon Romanovsky <leon@...nel.org>, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH net-next] can: sja1000: fix use after free in
 ems_pcmcia_add_card()

In the original code if ems_pcmcia_check_chan() returned false then
it called free_sja1000dev(dev) but did not set the error code or jump
to the clean up code.  This frees "dev" and leads to a use after free.

I flipped the ems_pcmcia_check_chan() check around to make the error
handling more consistent and readable.  That lets us pull the rest of
the code in one tab.

Fixes: fd734c6f25ae ("can/sja1000: add driver for EMS PCMCIA card")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
 drivers/net/can/sja1000/ems_pcmcia.c | 44 +++++++++++++++-------------
 1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/drivers/net/can/sja1000/ems_pcmcia.c b/drivers/net/can/sja1000/ems_pcmcia.c
index e21b169c14c0..271fe9444827 100644
--- a/drivers/net/can/sja1000/ems_pcmcia.c
+++ b/drivers/net/can/sja1000/ems_pcmcia.c
@@ -210,28 +210,30 @@ static int ems_pcmcia_add_card(struct pcmcia_device *pdev, unsigned long base)
 			(i * EMS_PCMCIA_CAN_CTRL_SIZE);
 
 		/* Check if channel is present */
-		if (ems_pcmcia_check_chan(priv)) {
-			priv->read_reg  = ems_pcmcia_read_reg;
-			priv->write_reg = ems_pcmcia_write_reg;
-			priv->can.clock.freq = EMS_PCMCIA_CAN_CLOCK;
-			priv->ocr = EMS_PCMCIA_OCR;
-			priv->cdr = EMS_PCMCIA_CDR;
-			priv->flags |= SJA1000_CUSTOM_IRQ_HANDLER;
-
-			/* Register SJA1000 device */
-			err = register_sja1000dev(dev);
-			if (err) {
-				free_sja1000dev(dev);
-				goto failure_cleanup;
-			}
-
-			card->channels++;
-
-			printk(KERN_INFO "%s: registered %s on channel "
-			       "#%d at 0x%p, irq %d\n", DRV_NAME, dev->name,
-			       i, priv->reg_base, dev->irq);
-		} else
+		if (!ems_pcmcia_check_chan(priv)) {
+			err = -EINVAL;
 			free_sja1000dev(dev);
+			goto failure_cleanup;
+		}
+		priv->read_reg  = ems_pcmcia_read_reg;
+		priv->write_reg = ems_pcmcia_write_reg;
+		priv->can.clock.freq = EMS_PCMCIA_CAN_CLOCK;
+		priv->ocr = EMS_PCMCIA_OCR;
+		priv->cdr = EMS_PCMCIA_CDR;
+		priv->flags |= SJA1000_CUSTOM_IRQ_HANDLER;
+
+		/* Register SJA1000 device */
+		err = register_sja1000dev(dev);
+		if (err) {
+			free_sja1000dev(dev);
+			goto failure_cleanup;
+		}
+
+		card->channels++;
+
+		printk(KERN_INFO "%s: registered %s on channel "
+		       "#%d at 0x%p, irq %d\n", DRV_NAME, dev->name,
+		       i, priv->reg_base, dev->irq);
 	}
 
 	err = request_irq(dev->irq, &ems_pcmcia_interrupt, IRQF_SHARED,
-- 
2.20.1