LOCKD: fix races in nsm_client_get
Commit e9406db20fecbfcab646bad157b4cfdc7cadddfb (lockd: per-net
NSM client creation and destruction helpers introduced) contains
a nasty race on initialisation of the per-net NSM client because
it doesn't check whether or not the client is set after grabbing
the nsm_create_mutex.
Reported-by: Nix <nix@esperi.org.uk>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org
diff --git a/fs/lockd/mon.c b/fs/lockd/mon.c
index e4fb3ba..fe69560 100644
--- a/fs/lockd/mon.c
+++ b/fs/lockd/mon.c
@@ -85,29 +85,38 @@
return rpc_create(&args);
}
+static struct rpc_clnt *nsm_client_set(struct lockd_net *ln,
+ struct rpc_clnt *clnt)
+{
+ spin_lock(&ln->nsm_clnt_lock);
+ if (ln->nsm_users == 0) {
+ if (clnt == NULL)
+ goto out;
+ ln->nsm_clnt = clnt;
+ }
+ clnt = ln->nsm_clnt;
+ ln->nsm_users++;
+out:
+ spin_unlock(&ln->nsm_clnt_lock);
+ return clnt;
+}
+
static struct rpc_clnt *nsm_client_get(struct net *net)
{
- static DEFINE_MUTEX(nsm_create_mutex);
- struct rpc_clnt *clnt;
+ struct rpc_clnt *clnt, *new;
struct lockd_net *ln = net_generic(net, lockd_net_id);
- spin_lock(&ln->nsm_clnt_lock);
- if (ln->nsm_users) {
- ln->nsm_users++;
- clnt = ln->nsm_clnt;
- spin_unlock(&ln->nsm_clnt_lock);
+ clnt = nsm_client_set(ln, NULL);
+ if (clnt != NULL)
goto out;
- }
- spin_unlock(&ln->nsm_clnt_lock);
- mutex_lock(&nsm_create_mutex);
- clnt = nsm_create(net);
- if (!IS_ERR(clnt)) {
- ln->nsm_clnt = clnt;
- smp_wmb();
- ln->nsm_users = 1;
- }
- mutex_unlock(&nsm_create_mutex);
+ clnt = new = nsm_create(net);
+ if (IS_ERR(clnt))
+ goto out;
+
+ clnt = nsm_client_set(ln, new);
+ if (clnt != new)
+ rpc_shutdown_client(new);
out:
return clnt;
}