NLM: Shrink the maximum request size of NLM4 requests

NLM version 4 requests estimate the call and reply header sizes rather
conservatively, using the very maximum size allowed in the protocol even
though Linux always uses only a small fraction of the allowable space.

Reduce the size of caller and lock arguments to conserve RPC buffer space
while XDR encoding NLM4 arguments.  Add compile-time checks to ensure the
hostname string won't overflow NLM protocol maximums.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/lockd/xdr.c

@@ -510,17 +510,20 @@ nlmclt_decode_res(struct rpc_rqst *req, __be32 *p, struct nlm_res *resp)
 	return 0;
 }
 
+#if (NLMCLNT_OHSIZE > XDR_MAX_NETOBJ)
+#  error "NLM host name cannot be larger than XDR_MAX_NETOBJ!"
+#endif
+
 /*
  * Buffer requirements for NLM
  */
 #define NLM_void_sz		0
 #define NLM_cookie_sz		1+XDR_QUADLEN(NLM_MAXCOOKIELEN)
-#define NLM_caller_sz		1+XDR_QUADLEN(sizeof(utsname()->nodename))
-#define NLM_netobj_sz		1+XDR_QUADLEN(XDR_MAX_NETOBJ)
-/* #define NLM_owner_sz		1+XDR_QUADLEN(NLM_MAXOWNER) */
+#define NLM_caller_sz		1+XDR_QUADLEN(NLMCLNT_OHSIZE)
+#define NLM_owner_sz		1+XDR_QUADLEN(NLMCLNT_OHSIZE)
 #define NLM_fhandle_sz		1+XDR_QUADLEN(NFS2_FHSIZE)
-#define NLM_lock_sz		3+NLM_caller_sz+NLM_netobj_sz+NLM_fhandle_sz
-#define NLM_holder_sz		4+NLM_netobj_sz
+#define NLM_lock_sz		3+NLM_caller_sz+NLM_owner_sz+NLM_fhandle_sz
+#define NLM_holder_sz		4+NLM_owner_sz
 
 #define NLM_testargs_sz		NLM_cookie_sz+1+NLM_lock_sz
 #define NLM_lockargs_sz		NLM_cookie_sz+4+NLM_lock_sz

fs/lockd/xdr4.c

@@ -516,17 +516,24 @@ nlm4clt_decode_res(struct rpc_rqst *req, __be32 *p, struct nlm_res *resp)
 	return 0;
 }
 
+#if (NLMCLNT_OHSIZE > XDR_MAX_NETOBJ)
+#  error "NLM host name cannot be larger than XDR_MAX_NETOBJ!"
+#endif
+
+#if (NLMCLNT_OHSIZE > NLM_MAXSTRLEN)
+#  error "NLM host name cannot be larger than NLM's maximum string length!"
+#endif
+
 /*
  * Buffer requirements for NLM
  */
 #define NLM4_void_sz		0
 #define NLM4_cookie_sz		1+XDR_QUADLEN(NLM_MAXCOOKIELEN)
-#define NLM4_caller_sz		1+XDR_QUADLEN(NLM_MAXSTRLEN)
-#define NLM4_netobj_sz		1+XDR_QUADLEN(XDR_MAX_NETOBJ)
-/* #define NLM4_owner_sz		1+XDR_QUADLEN(NLM4_MAXOWNER) */
+#define NLM4_caller_sz		1+XDR_QUADLEN(NLMCLNT_OHSIZE)
+#define NLM4_owner_sz		1+XDR_QUADLEN(NLMCLNT_OHSIZE)
 #define NLM4_fhandle_sz		1+XDR_QUADLEN(NFS3_FHSIZE)
-#define NLM4_lock_sz		5+NLM4_caller_sz+NLM4_netobj_sz+NLM4_fhandle_sz
-#define NLM4_holder_sz		6+NLM4_netobj_sz
+#define NLM4_lock_sz		5+NLM4_caller_sz+NLM4_owner_sz+NLM4_fhandle_sz
+#define NLM4_holder_sz		6+NLM4_owner_sz
 
 #define NLM4_testargs_sz	NLM4_cookie_sz+1+NLM4_lock_sz
 #define NLM4_lockargs_sz	NLM4_cookie_sz+4+NLM4_lock_sz

include/linux/lockd/lockd.h

@@ -88,7 +88,7 @@ struct nlm_wait;
 /*
  * Memory chunk for NLM client RPC request.
  */
-#define NLMCLNT_OHSIZE		(sizeof(utsname()->nodename)+10)
+#define NLMCLNT_OHSIZE		((__NEW_UTS_LEN) + 10u)
 struct nlm_rqst {
 	unsigned int		a_flags;	/* initial RPC task flags */
 	struct nlm_host *	a_host;		/* host handle */