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:
[<ffffffff81263105>] ? kobject_get_path+0x25/0x100
[<ffffffff81264354>] kobject_uevent_env+0x134/0x600
[<ffffffff8126482b>] kobject_uevent+0xb/0x10
[<ffffffff81262fa2>] kobject_delayed_cleanup+0xc2/0x1b0
[<ffffffff8106c047>] process_one_work+0x217/0x700
[<ffffffff8106bfdb>] ? process_one_work+0x1ab/0x700
[<ffffffff8106c64b>] worker_thread+0x11b/0x3a0
[<ffffffff8106c530>] ? process_one_work+0x700/0x700
[<ffffffff81074b70>] kthread+0xf0/0x110
[<ffffffff81074a80>] ? insert_kthread_work+0x80/0x80
[<ffffffff815673bc>] ret_from_fork+0x7c/0xb0
[<ffffffff81074a80>] ? 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 [<ffffffff81267ed0>] strlen+0x0/0x30
RSP <ffff88003b639c70>
---[ end trace 210f883ef80376aa ]---
Signed-off-by: Bart Van Assche <bvanass...@acm.org>
---
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 73f6c29..59dc808 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);
--
1.8.1.4
--
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