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>

3 files changed, 21 insertions, 11 deletions

diff --git a/fs/lockd/xdr.c b/fs/lockd/xdr.c
index 34dae5d70738..6aac4b2c9ff0 100644
--- a/fs/lockd/xdr.c
+++ b/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
diff --git a/fs/lockd/xdr4.c b/fs/lockd/xdr4.c
index a78240551219..7c8b679c394c 100644
--- a/fs/lockd/xdr4.c
+++ b/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
diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index ac25b5649c59..f6a81e0b1b93 100644
--- a/include/linux/lockd/lockd.h
+++ b/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 */