linux-kernel - [PATCH 3.12 096/111] xen: netback: read hotplug script once at start of day.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <8efd02c4eb48212294315514411a6e7a7e57e4da.1433943052.git.jslaby@suse.cz>
Date:	Wed, 10 Jun 2015 17:27:25 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 096/111] xen: netback: read hotplug script once at start of day.

From: Ian Campbell <Ian.Campbell@...rix.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

[ Upstream commit 31a418986a5852034d520a5bab546821ff1ccf3d ]

When we come to tear things down in netback_remove() and generate the
uevent it is possible that the xenstore directory has already been
removed (details below).

In such cases netback_uevent() won't be able to read the hotplug
script and will write a xenstore error node.

A recent change to the hypervisor exposed this race such that we now
sometimes lose it (where apparently we didn't ever before).

Instead read the hotplug script configuration during setup and use it
for the lifetime of the backend device.

The apparently more obvious fix of moving the transition to
state=Closed in netback_remove() to after the uevent does not work
because it is possible that we are already in state=Closed (in
reaction to the guest having disconnected as it shutdown). Being
already in Closed means the toolstack is at liberty to start tearing
down the xenstore directories. In principal it might be possible to
arrange to unregister the device sooner (e.g on transition to Closing)
such that xenstore would still be there but this state machine is
fragile and prone to anger...

A modern Xen system only relies on the hotplug uevent for driver
domains, when the backend is in the same domain as the toolstack it
will run the necessary setup/teardown directly in the correct sequence
wrt xenstore changes.

Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
Acked-by: Wei Liu <wei.liu2@...rix.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/net/xen-netback/xenbus.c | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 1b08d8798372..659a6f2abb67 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -33,6 +33,8 @@ struct backend_info {
 	enum xenbus_state frontend_state;
 	struct xenbus_watch hotplug_status_watch;
 	u8 have_hotplug_status_watch:1;
+
+	const char *hotplug_script;
 };
 
 static int connect_rings(struct backend_info *);
@@ -55,6 +57,7 @@ static int netback_remove(struct xenbus_device *dev)
 		xenvif_free(be->vif);
 		be->vif = NULL;
 	}
+	kfree(be->hotplug_script);
 	kfree(be);
 	dev_set_drvdata(&dev->dev, NULL);
 	return 0;
@@ -72,6 +75,7 @@ static int netback_probe(struct xenbus_device *dev,
 	struct xenbus_transaction xbt;
 	int err;
 	int sg;
+	const char *script;
 	struct backend_info *be = kzalloc(sizeof(struct backend_info),
 					  GFP_KERNEL);
 	if (!be) {
@@ -142,6 +146,15 @@ static int netback_probe(struct xenbus_device *dev,
 	if (err)
 		pr_debug("Error writing feature-split-event-channels\n");
 
+	script = xenbus_read(XBT_NIL, dev->nodename, "script", NULL);
+	if (IS_ERR(script)) {
+		err = PTR_ERR(script);
+		xenbus_dev_fatal(dev, err, "reading script");
+		goto fail;
+	}
+
+	be->hotplug_script = script;
+
 	err = xenbus_switch_state(dev, XenbusStateInitWait);
 	if (err)
 		goto fail;
@@ -172,22 +185,14 @@ static int netback_uevent(struct xenbus_device *xdev,
 			  struct kobj_uevent_env *env)
 {
 	struct backend_info *be = dev_get_drvdata(&xdev->dev);
-	char *val;
 
-	val = xenbus_read(XBT_NIL, xdev->nodename, "script", NULL);
-	if (IS_ERR(val)) {
-		int err = PTR_ERR(val);
-		xenbus_dev_fatal(xdev, err, "reading script");
-		return err;
-	} else {
-		if (add_uevent_var(env, "script=%s", val)) {
-			kfree(val);
-			return -ENOMEM;
-		}
-		kfree(val);
-	}
+	if (!be)
+		return 0;
+
+	if (add_uevent_var(env, "script=%s", be->hotplug_script))
+		return -ENOMEM;
 
-	if (!be || !be->vif)
+	if (!be->vif)
 		return 0;
 
 	return add_uevent_var(env, "vif=%s", be->vif->dev->name);
-- 
2.4.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/