nfsd: don't require low ports for gss requests

In a traditional NFS deployment using auth_unix, the clients are trusted
to correctly report the credentials of their logged-in users.  The
server assumes that only root on client machines is allowed to send
requests from low-numbered ports, so it can use the originating port
number to distinguish "real" NFS clients from NFS clients run by
ordinary users, to prevent ordinary users from spoofing credentials.

The originating port number on a gss-authenticated request is less
important.  The authentication ties the request to a user, and we take
it as proof that that user authorized the request.  The low port number
check no longer adds much.

So, don't enforce low port numbers in the auth_gss case.
Reviewed-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfsfh.c

@@ -87,13 +87,23 @@ nfsd_mode_check(struct svc_rqst *rqstp, struct dentry *dentry,
 	return nfserr_inval;
 }
 
+static bool nfsd_originating_port_ok(struct svc_rqst *rqstp, int flags)
+{
+	if (flags & NFSEXP_INSECURE_PORT)
+		return true;
+	/* We don't require gss requests to use low ports: */
+	if (rqstp->rq_cred.cr_flavor >= RPC_AUTH_GSS)
+		return true;
+	return test_bit(RQ_SECURE, &rqstp->rq_flags);
+}
+
 static __be32 nfsd_setuser_and_check_port(struct svc_rqst *rqstp,
 					  struct svc_export *exp)
 {
 	int flags = nfsexp_flags(rqstp, exp);
 
 	/* Check if the request originated from a secure port. */
-	if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && !(flags & NFSEXP_INSECURE_PORT)) {
+	if (!nfsd_originating_port_ok(rqstp, flags)) {
 		RPC_IFDEBUG(char buf[RPC_MAX_ADDRBUFLEN]);
 		dprintk("nfsd: request from insecure port %s!\n",
 		        svc_print_addr(rqstp, buf, sizeof(buf)));