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@xxxxxxxxxx>
CC: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Signed-off-by: Gregory Haskins <ghaskins@xxxxxxxxxx>
---
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 f9d7e1d..4a073ee 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -260,6 +260,8 @@ static int eventfd_notifier_wakeup(wait_queue_t *wait, unsigned mode,
en->ops->signal(en);
if (flags & POLLHUP) {
+ struct module *owner = en->owner;
+
/*
* The POLLHUP is called unlocked, so it theoretically should
* be safe to remove ourselves from the wqh using the locked
@@ -267,6 +269,8 @@ static int eventfd_notifier_wakeup(wait_queue_t *wait, unsigned mode,
*/
remove_wait_queue(en->wqh, &en->wait);
en->ops->release(en);
+
+ module_put(owner);
}
return 0;
@@ -291,6 +295,9 @@ int eventfd_notifier_register(struct file *file, struct eventfd_notifier *en)
if (file->f_op != &eventfd_fops)
return -EINVAL;
+ if (!try_module_get(en->owner))
+ return -EINVAL;
+
/*
* Install our own custom wake-up handling so we are notified via
* a callback whenever someone signals the underlying eventfd
@@ -310,6 +317,7 @@ int eventfd_notifier_unregister(struct file *file, struct eventfd_notifier *en)
return -EINVAL;
remove_wait_queue(en->wqh, &en->wait);
+ module_put(en->owner);
return 0;
}
diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
index 802b59d..7e015f0 100644
--- a/include/linux/eventfd.h
+++ b/include/linux/eventfd.h
@@ -12,6 +12,7 @@
#include <linux/poll.h>
#include <linux/file.h>
#include <linux/list.h>
+#include <linux/module.h>
struct eventfd_notifier;
@@ -21,6 +22,7 @@ struct eventfd_notifier_ops {
};
struct eventfd_notifier {
+ struct module *owner;
poll_table pt;
wait_queue_head_t *wqh;
wait_queue_t wait;
@@ -31,6 +33,7 @@ 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;
en->ops = ops;
}
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