lockd: fix race in nlm_release()
The sm_count is decremented to zero but left on the nsm_handles list.
So in the space between decrementing sm_count and acquiring nsm_mutex,
it is possible for another task to find this nsm_handle, increment the
use count and then enter nsm_release itself.
Thus there's nothing to prevent the nsm being freed before we acquire
nsm_mutex here.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/fs/lockd/host.c b/fs/lockd/host.c
index c3f1194..960911c 100644
--- a/fs/lockd/host.c
+++ b/fs/lockd/host.c
@@ -529,12 +529,10 @@
{
if (!nsm)
return;
+ mutex_lock(&nsm_mutex);
if (atomic_dec_and_test(&nsm->sm_count)) {
- mutex_lock(&nsm_mutex);
- if (atomic_read(&nsm->sm_count) == 0) {
- list_del(&nsm->sm_link);
- kfree(nsm);
- }
- mutex_unlock(&nsm_mutex);
+ list_del(&nsm->sm_link);
+ kfree(nsm);
}
+ mutex_unlock(&nsm_mutex);
}