nfsd: return errors, not NULL, from export functions

I converted the various export-returning functions to return -ENOENT instead
of NULL, but missed a few cases.

This particular case could cause actual bugs in the case of a krb5 client that
doesn't match any ip-based client and that is trying to access a filesystem
not exported to krb5 clients.
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Acked-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nfsd/export.c

@@ -1265,7 +1265,7 @@ struct svc_export *
 rqst_exp_get_by_name(struct svc_rqst *rqstp, struct vfsmount *mnt,
 		struct dentry *dentry)
 {
-	struct svc_export *gssexp, *exp = NULL;
+	struct svc_export *gssexp, *exp = ERR_PTR(-ENOENT);
 
 	if (rqstp->rq_client == NULL)
 		goto gss;
@@ -1288,7 +1288,7 @@ gss:
 						&rqstp->rq_chandle);
 	if (PTR_ERR(gssexp) == -ENOENT)
 		return exp;
-	if (exp && !IS_ERR(exp))
+	if (!IS_ERR(exp))
 		exp_put(exp);
 	return gssexp;
 }
@@ -1296,7 +1296,7 @@ gss:
 struct svc_export *
 rqst_exp_find(struct svc_rqst *rqstp, int fsid_type, u32 *fsidv)
 {
-	struct svc_export *gssexp, *exp = NULL;
+	struct svc_export *gssexp, *exp = ERR_PTR(-ENOENT);
 
 	if (rqstp->rq_client == NULL)
 		goto gss;
@@ -1318,7 +1318,7 @@ gss:
 						&rqstp->rq_chandle);
 	if (PTR_ERR(gssexp) == -ENOENT)
 		return exp;
-	if (exp && !IS_ERR(exp))
+	if (!IS_ERR(exp))
 		exp_put(exp);
 	return gssexp;
 }