can: peak_pci: prevent use after free at netdev removal

commit 0b5a958cf4df3a5cd578b861471e62138f55c85e upstream.

As remarked by Christopher R. Baker in his post at

http://marc.info/?l=linux-can&m=139707295706465&w=2

there's a possibility for an use after free condition at device removal.

This simplified patch introduces an additional variable to prevent the issue.
Thanks for catching this.

Reported-by: Christopher R. Baker <cbaker@rec.ri.cmu.edu>
Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/net/can/sja1000/peak_pci.c b/drivers/net/can/sja1000/peak_pci.c
index 214795945bc449d79329bbf2b82500eb9e1f19a3..5192f8615258c1b1afe776b04c56ba17400a23e4 100644 (file)
--- a/drivers/net/can/sja1000/peak_pci.c
+++ b/drivers/net/can/sja1000/peak_pci.c
@@ -98,7 +98,7 @@ static int __devinit peak_pci_probe(struct pci_dev *pdev,
 {
        struct sja1000_priv *priv;
        struct peak_pci_chan *chan;
-       struct net_device *dev;
+       struct net_device *dev, *prev_dev;
        void __iomem *cfg_base, *reg_base;
        u16 sub_sys_id, icr;
        int i, err, channels;
@@ -213,11 +213,13 @@ failure_remove_channels:
        /* Disable interrupts */
        writew(0x0, cfg_base + PITA_ICR + 2);
 
-       for (dev = pci_get_drvdata(pdev); dev; dev = chan->prev_dev) {
-               unregister_sja1000dev(dev);
-               free_sja1000dev(dev);
+       for (dev = pci_get_drvdata(pdev); dev; dev = prev_dev) {
                priv = netdev_priv(dev);
                chan = priv->priv;
+               prev_dev = chan->prev_dev;
+
+               unregister_sja1000dev(dev);
+               free_sja1000dev(dev);
        }
 
        pci_iounmap(pdev, reg_base);
@@ -247,10 +249,12 @@ static void __devexit peak_pci_remove(struct pci_dev *pdev)
 
        /* Loop over all registered devices */
        while (1) {
+               struct net_device *prev_dev = chan->prev_dev;
+
                dev_info(&pdev->dev, "removing device %s\n", dev->name);
                unregister_sja1000dev(dev);
                free_sja1000dev(dev);
-               dev = chan->prev_dev;
+               dev = prev_dev;
                if (!dev)
                        break;
                priv = netdev_priv(dev);