NFSv4: Fix EXCHANGE_ID corrupt verifier issue

The verifier is allocated on the stack, but the EXCHANGE_ID RPC call was
changed to be asynchronous by commit 8d89bd70. If we interrrupt
the call to rpc_wait_for_completion_task(), we can therefore end up
transmitting random stack contents in lieu of the verifier.

Fixes: 8d89bd70 ("NFS setup async exchange_id")
Cc: stable@vger.kernel.org # v4.9+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/nfs4proc.c

@@ -7460,7 +7460,7 @@ static void nfs4_exchange_id_done(struct rpc_task *task, void *data)
 			cdata->res.server_scope = NULL;
 		}
 		/* Save the EXCHANGE_ID verifier session trunk tests */
-		memcpy(clp->cl_confirm.data, cdata->args.verifier->data,
+		memcpy(clp->cl_confirm.data, cdata->args.verifier.data,
 		       sizeof(clp->cl_confirm.data));
 	}
 out:
@@ -7497,7 +7497,6 @@ static const struct rpc_call_ops nfs4_exchange_id_call_ops = {
 static int _nfs4_proc_exchange_id(struct nfs_client *clp, struct rpc_cred *cred,
 			u32 sp4_how, struct rpc_xprt *xprt)
 {
-	nfs4_verifier verifier;
 	struct rpc_message msg = {
 		.rpc_proc = &nfs4_procedures[NFSPROC4_CLNT_EXCHANGE_ID],
 		.rpc_cred = cred,
@@ -7521,8 +7520,7 @@ static int _nfs4_proc_exchange_id(struct nfs_client *clp, struct rpc_cred *cred,
 		return -ENOMEM;
 	}
 
-	if (!xprt)
-		nfs4_init_boot_verifier(clp, &verifier);
+	nfs4_init_boot_verifier(clp, &calldata->args.verifier);
 
 	status = nfs4_init_uniform_client_string(clp);
 	if (status)
@@ -7563,9 +7561,8 @@ static int _nfs4_proc_exchange_id(struct nfs_client *clp, struct rpc_cred *cred,
 		task_setup_data.rpc_xprt = xprt;
 		task_setup_data.flags =
 				RPC_TASK_SOFT|RPC_TASK_SOFTCONN|RPC_TASK_ASYNC;
-		calldata->args.verifier = &clp->cl_confirm;
-	} else {
-		calldata->args.verifier = &verifier;
+		memcpy(calldata->args.verifier.data, clp->cl_confirm.data,
+				sizeof(calldata->args.verifier.data));
 	}
 	calldata->args.client = clp;
 #ifdef CONFIG_NFS_V4_1_MIGRATION

fs/nfs/nfs4xdr.c

@@ -1785,7 +1785,7 @@ static void encode_exchange_id(struct xdr_stream *xdr,
 	int len = 0;
 
 	encode_op_hdr(xdr, OP_EXCHANGE_ID, decode_exchange_id_maxsz, hdr);
-	encode_nfs4_verifier(xdr, args->verifier);
+	encode_nfs4_verifier(xdr, &args->verifier);
 
 	encode_string(xdr, strlen(args->client->cl_owner_id),
 			args->client->cl_owner_id);

include/linux/nfs_xdr.h

@@ -1235,7 +1235,7 @@ struct nfs41_state_protection {
 
 struct nfs41_exchange_id_args {
 	struct nfs_client		*client;
-	nfs4_verifier			*verifier;
+	nfs4_verifier			verifier;
 	u32				flags;
 	struct nfs41_state_protection	state_protect;
 };