SUNRPC: Fix a race in rpc_info_open

There is a race between rpc_info_open and rpc_release_client()
in that nothing stops a process from opening the file after
the clnt->cl_kref goes to zero.

Fix this by using atomic_inc_unless_zero()...

Reported-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org

1 files changed, 12 insertions, 14 deletions

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 657aac630fc9..3a8f53e7ba07 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -226,7 +226,7 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
                         goto out_no_principal;
         }
 
-        kref_init(&clnt->cl_kref);
+        atomic_set(&clnt->cl_count, 1);
 
         err = rpc_setup_pipedir(clnt, program->pipe_dir_name);
         if (err < 0)
@@ -390,14 +390,14 @@ rpc_clone_client(struct rpc_clnt *clnt)
                 if (new->cl_principal == NULL)
                         goto out_no_principal;
         }
-        kref_init(&new->cl_kref);
+        atomic_set(&new->cl_count, 1);
         err = rpc_setup_pipedir(new, clnt->cl_program->pipe_dir_name);
         if (err != 0)
                 goto out_no_path;
         if (new->cl_auth)
                 atomic_inc(&new->cl_auth->au_count);
         xprt_get(clnt->cl_xprt);
-        kref_get(&clnt->cl_kref);
+        atomic_inc(&clnt->cl_count);
         rpc_register_client(new);
         rpciod_up();
         return new;
@@ -465,10 +465,8 @@ EXPORT_SYMBOL_GPL(rpc_shutdown_client);
  * Free an RPC client
  */
 static void
-rpc_free_client(struct kref *kref)
+rpc_free_client(struct rpc_clnt *clnt)
 {
-        struct rpc_clnt *clnt = container_of(kref, struct rpc_clnt, cl_kref);
-
         dprintk("RPC:       destroying %s client for %s\n",
                         clnt->cl_protname, clnt->cl_server);
         if (!IS_ERR(clnt->cl_path.dentry)) {
@@ -495,12 +493,10 @@ out_free:
  * Free an RPC client
  */
 static void
-rpc_free_auth(struct kref *kref)
+rpc_free_auth(struct rpc_clnt *clnt)
 {
-        struct rpc_clnt *clnt = container_of(kref, struct rpc_clnt, cl_kref);
-
         if (clnt->cl_auth == NULL) {
-                rpc_free_client(kref);
+                rpc_free_client(clnt);
                 return;
         }
 
@@ -509,10 +505,11 @@ rpc_free_auth(struct kref *kref)
          *       release remaining GSS contexts. This mechanism ensures
          *       that it can do so safely.
          */
-        kref_init(kref);
+        atomic_inc(&clnt->cl_count);
         rpcauth_release(clnt->cl_auth);
         clnt->cl_auth = NULL;
-        kref_put(kref, rpc_free_client);
+        if (atomic_dec_and_test(&clnt->cl_count))
+                rpc_free_client(clnt);
 }
 
 /*
@@ -525,7 +522,8 @@ rpc_release_client(struct rpc_clnt *clnt)
 
         if (list_empty(&clnt->cl_tasks))
                 wake_up(&destroy_wait);
-        kref_put(&clnt->cl_kref, rpc_free_auth);
+        if (atomic_dec_and_test(&clnt->cl_count))
+                rpc_free_auth(clnt);
 }
 
 /**
@@ -588,7 +586,7 @@ void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt)
         if (clnt != NULL) {
                 rpc_task_release_client(task);
                 task->tk_client = clnt;
-                kref_get(&clnt->cl_kref);
+                atomic_inc(&clnt->cl_count);
                 if (clnt->cl_softrtry)
                         task->tk_flags |= RPC_TASK_SOFT;
                 /* Add to the client's list of all tasks */