[PATCH] xen-netfront: avoid crashing on resume after a failure in talk_to_netback()

From: Vitaly Kuznetsov
Date: Thu May 04 2017 - 08:23:22 EST

Unavoidable crashes in netfront_resume() and netback_changed() after a
previous fail in talk_to_netback() (e.g. when we fail to read MAC from
xenstore) were discovered. The failure path in talk_to_netback() does
unregister/free for netdev but we don't reset drvdata and we try accessing
it again after resume.

Reset drvdata in netback_changed() the same way we reset it in
netfront_probe() and check for NULL in both netfront_resume() and
netback_changed() to properly handle the situation.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
I apologize for sending this during the merge window, I'm not sure if this
needs to go through xen or netdev tree. I think the fix is simple enough
and it would make sense to squeeze it in 4.12 if possible. Thanks.
drivers/net/xen-netfront.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 6ffc482..92f746c 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1426,6 +1426,9 @@ static int netfront_resume(struct xenbus_device *dev)
struct netfront_info *info = dev_get_drvdata(&dev->dev);

+ if (!info)
+ return 0;
dev_dbg(&dev->dev, "%s\n", dev->nodename);

@@ -1936,6 +1939,7 @@ static int talk_to_netback(struct xenbus_device *dev,
+ dev_set_drvdata(&dev->dev, NULL);
return err;

@@ -1997,7 +2001,12 @@ static void netback_changed(struct xenbus_device *dev,
enum xenbus_state backend_state)
struct netfront_info *np = dev_get_drvdata(&dev->dev);
- struct net_device *netdev = np->netdev;
+ struct net_device *netdev;
+ if (!np)
+ return;
+ netdev = np->netdev;

dev_dbg(&dev->dev, "%s\n", xenbus_strstate(backend_state));