nfsd: restrict rd_maxcount to svc_max_payload in nfsd_encode_readdir

nfsd4_readdir_rsize restricts rd_maxcount to svc_max_payload when
estimating the size of the readdir reply, but nfsd_encode_readdir
restricts it to INT_MAX when encoding the reply.  This can result in log
messages like "kernel: RPC request reserved 32896 but used 1049444".

Restrict rd_dircount similarly (no reason it should be larger than
svc_max_payload).
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -3651,7 +3651,8 @@ nfsd4_encode_readdir(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4
 		nfserr = nfserr_resource;
 		goto err_no_verf;
 	}
-	maxcount = min_t(u32, readdir->rd_maxcount, INT_MAX);
+	maxcount = svc_max_payload(resp->rqstp);
+	maxcount = min_t(u32, readdir->rd_maxcount, maxcount);
 	/*
 	 * Note the rfc defines rd_maxcount as the size of the
 	 * READDIR4resok structure, which includes the verifier above
@@ -3665,7 +3666,7 @@ nfsd4_encode_readdir(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4
 
 	/* RFC 3530 14.2.24 allows us to ignore dircount when it's 0: */
 	if (!readdir->rd_dircount)
-		readdir->rd_dircount = INT_MAX;
+		readdir->rd_dircount = svc_max_payload(resp->rqstp);
 
 	readdir->xdr = xdr;
 	readdir->rd_maxcount = maxcount;