[PATCH] nfsd: prevent NULL ptr derefs on fault injection

[Sasha Levin <sasha.levin@oracle.com>]

A recent patch series has moved hashtable initialization to when the net
struct is initialized.

When injecting faults, we tried accessing the hashtables even if the struct
wasn't really initialized (nfsd wasn't in use) - this caused a NULL ptr
deref.

A simple test would be:

	echo 1 > /sys/kernel/debug/nfsd/forget_locks

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 fs/nfsd/netns.h     | 3 +++
 fs/nfsd/nfs4state.c | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 227b93e..c5806a57 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -83,5 +83,8 @@ struct nfsd_net {
 	struct delayed_work laundromat_work;
 };
 
+/* Simple check to find out if a given net was properly initialized */
+#define nfsd_netns_ready(nn) ((nn)->sessionid_hashtbl)
+
 extern int nfsd_net_id;
 #endif /* __NFSD_NETNS_H__ */
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index e75872f..0e7428c 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4598,6 +4598,9 @@ void nfsd_forget_clients(u64 num)
 	int count = 0;
 	struct nfsd_net *nn = net_generic(current->nsproxy->net_ns, nfsd_net_id);
 
+	if (!nfsd_netns_ready(nn))
+		return;
+
 	nfs4_lock_state();
 	list_for_each_entry_safe(clp, next, &nn->client_lru, cl_lru) {
 		expire_client(clp);
@@ -4643,6 +4646,9 @@ void nfsd_forget_locks(u64 num)
 	int count;
 	struct nfsd_net *nn = net_generic(&init_net, nfsd_net_id);
 
+	if (!nfsd_netns_ready(nn))
+		return;
+
 	nfs4_lock_state();
 	count = nfsd_release_n_owners(num, false, release_lockowner_sop, nn);
 	nfs4_unlock_state();
@@ -4655,6 +4661,9 @@ void nfsd_forget_openowners(u64 num)
 	int count;
 	struct nfsd_net *nn = net_generic(&init_net, nfsd_net_id);
 
+	if (!nfsd_netns_ready(nn))
+		return;
+
 	nfs4_lock_state();
 	count = nfsd_release_n_owners(num, true, release_openowner_sop, nn);
 	nfs4_unlock_state();
-- 
1.8.0