When the refcount is decreased to 0, the rbd_client_release() is called.
Before CPU0 reaches the race point (1), CPU1 may obtain the spinlock
and traverse the linked list to find 'rbdc'. Although CPU1 will call
kref_get() to increase the refcount, it is obviously too late. CPU0 will
release 'rbdc' directly, CPU1 then accesses 'rbdc' and triggers UAF.
Use kref_put_lock() to ensure that both the operations of decrease
refcount to 0 and link deletion are lock protected eliminates this risk.
CPU0 CPU1
rbd_client_release():
<-------- (1)
spin_lock(&rbd_client_list_lock);
list_del(&rbdc->node);
spin_unlock(&rbd_client_list_lock);
kfree(rbdc);
<-------- use-after-free
Fixes: 602adf400201 ("rbd: introduce rados block device (rbd), based on libceph")
Signed-off-by: Zhen Lei <[email protected]>
---
drivers/block/rbd.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 531d390902dd..3a8989bf8e9c 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -875,11 +875,11 @@ static void rbd_client_release(struct kref *kref)
{
struct rbd_client *rbdc = container_of(kref, struct rbd_client, kref);
- dout("%s: rbdc %p\n", __func__, rbdc);
- spin_lock(&rbd_client_list_lock);
list_del(&rbdc->node);
spin_unlock(&rbd_client_list_lock);
+ dout("%s: rbdc %p\n", __func__, rbdc);
+
ceph_destroy_client(rbdc->client);
kfree(rbdc);
}
@@ -891,7 +891,8 @@ static void rbd_client_release(struct kref *kref)
static void rbd_put_client(struct rbd_client *rbdc)
{
if (rbdc)
- kref_put(&rbdc->kref, rbd_client_release);
+ kref_put_lock(&rbdc->kref,
+ rbd_client_release, &rbd_client_list_lock);
}
/*
--
2.25.1