[KVM-RFC PATCH 2/2] eventfd: add module reference counting support for registered notifiers

Gregory Haskins
2009-06-16T02:30:52Z

Michael Tsirkin found a race condition in the irqfd code where we may
allow the underlying eventfd object to race with the rmmod of kvm.ko.

Since we now use eventfd_notifier for irqfd, lets add a struct module *owner
field to properly maintain references to our registered signal handlers.

Found-by: Michael S. Tsirkin <mst@redhat.com>
CC: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
---

fs/eventfd.c | 8 ++++++++
include/linux/eventfd.h | 3 +++
2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/fs/eventfd.c b/fs/eventfd.c
index 505d5de..babedb3 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -108,9 +108,12 @@ static int eventfd_release(struct inode *inode, struct file *file)
* path
*/
list_for_each_entry_safe(en, tmp, &ctx->nh, list) {
+ struct module *owner = en->owner;
+
list_del(&en->list);
if (en->ops->release)
en->ops->release(en);
+ module_put(owner);
}

synchronize_srcu(&ctx->srcu);
@@ -261,6 +264,9 @@ static int _eventfd_notifier_register(struct eventfd_ctx *ctx,
{
unsigned long flags;

+ if (!try_module_get(en->owner))
+ return -EINVAL;
+
spin_lock_irqsave(&ctx->wqh.lock, flags);
list_add_tail_rcu(&en->list, &ctx->nh);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
@@ -292,6 +298,8 @@ int eventfd_notifier_unregister(struct file *file, struct eventfd_notifier *en)

synchronize_srcu(&ctx->srcu);

+ module_put(en->owner);
+
return 0;
}
EXPORT_SYMBOL_GPL(eventfd_notifier_unregister);
diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
index 0218cf6..f534bcd 100644
--- a/include/linux/eventfd.h
+++ b/include/linux/eventfd.h
@@ -9,6 +9,7 @@
#define _LINUX_EVENTFD_H

#include <linux/list.h>
+#include <linux/module.h>

struct eventfd_notifier;

@@ -18,6 +19,7 @@ struct eventfd_notifier_ops {
};

struct eventfd_notifier {
+ struct module *owner;
struct list_head list;
const struct eventfd_notifier_ops *ops;
};
@@ -26,6 +28,7 @@ static inline void eventfd_notifier_init(struct eventfd_notifier *en,
const struct eventfd_notifier_ops *ops)
{
memset(en, 0, sizeof(*en));
+ en->owner = THIS_MODULE;
INIT_LIST_HEAD(&en->list);
en->ops = ops;
}