NFSv4: remove callback IDR entry on client allocation failure

nfs4_alloc_client() allocates an NFSv4.0 callback identifier before it
finishes setting up the client. If any later initialization step fails,
the error path frees the nfs_client directly with nfs_free_client(). That
bypasses nfs_put_client(), which is where the callback IDR entry is
removed during normal teardown.

A failed allocation can therefore leave cb_ident_idr pointing at a freed
nfs_client. A later NFSv4.0 callback lookup by cb_ident would find the
stale pointer and take a reference to it.

Make the callback IDR removal helper callable by the allocation failure
path, and remove the callback identifier before freeing the client.

This was found by a local static-analysis checker for publish-before-free
lifetime bugs and confirmed by manual inspection.

Fixes: f4eecd5da3 ("NFS implement v4.0 callback_ident")
Signed-off-by: Ruoyu Wang <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>

fs/nfs/client.c

@@ -215,10 +215,22 @@ static void nfs_cb_idr_remove_locked(struct nfs_client *clp)
 {
 	struct nfs_net *nn = net_generic(clp->cl_net, nfs_net_id);
 
-	if (clp->cl_cb_ident)
+	if (clp->cl_cb_ident) {
 		idr_remove(&nn->cb_ident_idr, clp->cl_cb_ident);
+		clp->cl_cb_ident = 0;
+	}
 }
 
+void nfs_cb_idr_remove(struct nfs_client *clp)
+{
+	struct nfs_net *nn = net_generic(clp->cl_net, nfs_net_id);
+
+	spin_lock(&nn->nfs_client_lock);
+	nfs_cb_idr_remove_locked(clp);
+	spin_unlock(&nn->nfs_client_lock);
+}
+EXPORT_SYMBOL_GPL(nfs_cb_idr_remove);
+
 static void pnfs_init_server(struct nfs_server *server)
 {
 	rpc_init_wait_queue(&server->roc_rpcwaitq, "pNFS ROC");

fs/nfs/internal.h

@@ -225,6 +225,7 @@ void nfs_server_copy_userdata(struct nfs_server *, struct nfs_server *);
 
 extern void nfs_put_client(struct nfs_client *);
 extern void nfs_free_client(struct nfs_client *);
+void nfs_cb_idr_remove(struct nfs_client *clp);
 extern struct nfs_client *nfs4_find_client_ident(struct net *, int);
 extern struct nfs_client *
 nfs4_find_client_sessionid(struct net *, const struct sockaddr *,

fs/nfs/nfs4client.c

@@ -261,6 +261,7 @@ struct nfs_client *nfs4_alloc_client(const struct nfs_client_initdata *cl_init)
 	return clp;
 
 error:
+	nfs_cb_idr_remove(clp);
 	nfs_free_client(clp);
 	return ERR_PTR(err);
 }