From 174be70b638ceb1038f466b5ca014f6b1d9c8a59 Mon Sep 17 00:00:00 2001 From: Bart Van Assche Date: Sat, 4 Jan 2014 14:21:42 +0100 Subject: [PATCH] driver-core: Fix use-after-free triggered by bus_unregister() Avoid that bus_unregister() triggers a use-after-free with CONFIG_DEBUG_KOBJECT_RELEASE=y. This patch avoids that the following sequence triggers a kernel crash with memory poisoning enabled: * bus_register() * driver_register() * driver_unregister() * bus_unregister() The above sequence causes the bus private data to be freed from inside the bus_unregister() call although it is not guaranteed in that function that the reference count on the bus private data has dropped to zero. As an example, with CONFIG_DEBUG_KOBJECT_RELEASE=y the ${bus}/drivers kobject is still holding a reference on bus->p->subsys.kobj via its parent pointer at the time the bus private data is freed. Fix this by deferring freeing the bus private data until the last kobject_put() call on bus->p->subsys.kobj. The kernel oops triggered by the above sequence and with memory poisoning enabled and that is fixed by this patch is as follows: general protection fault: 0000 [#1] PREEMPT SMP CPU: 3 PID: 2711 Comm: kworker/3:32 Tainted: G W O 3.13.0-rc4-debug+ #1 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 Workqueue: events kobject_delayed_cleanup task: ffff880037f866d0 ti: ffff88003b638000 task.ti: ffff88003b638000 Call Trace: [] ? kobject_get_path+0x25/0x100 [] kobject_uevent_env+0x134/0x600 [] kobject_uevent+0xb/0x10 [] kobject_delayed_cleanup+0xc2/0x1b0 [] process_one_work+0x217/0x700 [] ? process_one_work+0x1ab/0x700 [] worker_thread+0x11b/0x3a0 [] ? process_one_work+0x700/0x700 [] kthread+0xf0/0x110 [] ? insert_kthread_work+0x80/0x80 [] ret_from_fork+0x7c/0xb0 [] ? insert_kthread_work+0x80/0x80 Code: 89 f8 48 89 e5 f6 82 c0 27 63 81 20 74 15 0f 1f 44 00 00 48 83 c0 01 0f b6 10 f6 82 c0 27 63 81 20 75 f0 5d c3 66 0f 1f 44 00 00 <80> 3f 00 55 48 89 e5 74 15 48 89 f8 0f 1f 40 00 48 83 c0 01 80 RIP [] strlen+0x0/0x30 RSP ---[ end trace 210f883ef80376aa ]--- Signed-off-by: Bart Van Assche Acked-by: Ming Lei Signed-off-by: Greg Kroah-Hartman --- drivers/base/bus.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/drivers/base/bus.c b/drivers/base/bus.c index 73f6c2925281..59dc8086e4fa 100644 --- a/drivers/base/bus.c +++ b/drivers/base/bus.c @@ -146,8 +146,19 @@ void bus_remove_file(struct bus_type *bus, struct bus_attribute *attr) } EXPORT_SYMBOL_GPL(bus_remove_file); +static void bus_release(struct kobject *kobj) +{ + struct subsys_private *priv = + container_of(kobj, typeof(*priv), subsys.kobj); + struct bus_type *bus = priv->bus; + + kfree(priv); + bus->p = NULL; +} + static struct kobj_type bus_ktype = { .sysfs_ops = &bus_sysfs_ops, + .release = bus_release, }; static int bus_uevent_filter(struct kset *kset, struct kobject *kobj) @@ -953,8 +964,6 @@ void bus_unregister(struct bus_type *bus) kset_unregister(bus->p->devices_kset); bus_remove_file(bus, &bus_attr_uevent); kset_unregister(&bus->p->subsys); - kfree(bus->p); - bus->p = NULL; } EXPORT_SYMBOL_GPL(bus_unregister);