From a4ee8d978e47e79d536226dccb48991f70091168 Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Tue, 23 Oct 2012 13:51:58 -0400 Subject: 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 Signed-off-by: Trond Myklebust 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 @@ static struct rpc_clnt *nsm_create(struct net *net) 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; } -- cgit v0.10.2