nfsd4: allow numeric idmapping

Mimic the client side by providing a module parameter that turns off
idmapping in the auth_sys case, for backwards compatibility with NFSv2
and NFSv3.

Unlike in the client case, we don't have any way to negotiate, since the
client can return an error to us if it doesn't like the id that we
return to it in (for example) a getattr call.

However, it has always been possible for servers to return numeric id's,
and as far as we're aware clients have always been able to handle them.

Also, in the auth_sys case clients already need to have numeric id's the
same between client and server.

Therefore we believe it's safe to default this to on; but the module
parameter is available to return to previous behavior if this proves to
be a problem in some unexpected setup.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

Documentation/kernel-parameters.txt

@@ -1686,6 +1686,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			The default is to send the implementation identification
 			information.
 
+	nfsd.nfs4_disable_idmapping=
+			[NFSv4] When set to the default of '1', the NFSv4
+			server will return only numeric uids and gids to
+			clients using auth_sys, and will accept numeric uids
+			and gids from such clients.  This is intended to ease
+			migration from NFSv2/v3.
 
 	objlayoutdriver.osd_login_prog=
 			[NFS] [OBJLAYOUT] sets the pathname to the program which

fs/nfsd/nfs4idmap.c

@@ -40,6 +40,14 @@
 #include "idmap.h"
 #include "nfsd.h"
 
+/*
+ * Turn off idmapping when using AUTH_SYS.
+ */
+static bool nfs4_disable_idmapping = true;
+module_param(nfs4_disable_idmapping, bool, 0644);
+MODULE_PARM_DESC(nfs4_disable_idmapping,
+		"Turn off server's NFSv4 idmapping when using 'sec=sys'");
+
 /*
  * Cache entry
  */
@@ -561,28 +569,65 @@ idmap_id_to_name(struct svc_rqst *rqstp, int type, uid_t id, char *name)
 	return ret;
 }
 
+static bool
+numeric_name_to_id(struct svc_rqst *rqstp, int type, const char *name, u32 namelen, uid_t *id)
+{
+	int ret;
+	char buf[11];
+
+	if (namelen + 1 > sizeof(buf))
+		/* too long to represent a 32-bit id: */
+		return false;
+	/* Just to make sure it's null-terminated: */
+	memcpy(buf, name, namelen);
+	buf[namelen] = '\0';
+	ret = strict_strtoul(name, 10, (unsigned long *)id);
+	return ret == 0;
+}
+
+static __be32
+do_name_to_id(struct svc_rqst *rqstp, int type, const char *name, u32 namelen, uid_t *id)
+{
+	if (nfs4_disable_idmapping && rqstp->rq_flavor < RPC_AUTH_GSS)
+		if (numeric_name_to_id(rqstp, type, name, namelen, id))
+			return 0;
+		/*
+		 * otherwise, fall through and try idmapping, for
+		 * backwards compatibility with clients sending names:
+		 */
+	return idmap_name_to_id(rqstp, type, name, namelen, id);
+}
+
+static int
+do_id_to_name(struct svc_rqst *rqstp, int type, uid_t id, char *name)
+{
+	if (nfs4_disable_idmapping && rqstp->rq_flavor < RPC_AUTH_GSS)
+		return sprintf(name, "%u", id);
+	return idmap_id_to_name(rqstp, type, id, name);
+}
+
 __be32
 nfsd_map_name_to_uid(struct svc_rqst *rqstp, const char *name, size_t namelen,
 		__u32 *id)
 {
-	return idmap_name_to_id(rqstp, IDMAP_TYPE_USER, name, namelen, id);
+	return do_name_to_id(rqstp, IDMAP_TYPE_USER, name, namelen, id);
 }
 
 __be32
 nfsd_map_name_to_gid(struct svc_rqst *rqstp, const char *name, size_t namelen,
 		__u32 *id)
 {
-	return idmap_name_to_id(rqstp, IDMAP_TYPE_GROUP, name, namelen, id);
+	return do_name_to_id(rqstp, IDMAP_TYPE_GROUP, name, namelen, id);
 }
 
 int
 nfsd_map_uid_to_name(struct svc_rqst *rqstp, __u32 id, char *name)
 {
-	return idmap_id_to_name(rqstp, IDMAP_TYPE_USER, id, name);
+	return do_id_to_name(rqstp, IDMAP_TYPE_USER, id, name);
 }
 
 int
 nfsd_map_gid_to_name(struct svc_rqst *rqstp, __u32 id, char *name)
 {
-	return idmap_id_to_name(rqstp, IDMAP_TYPE_GROUP, id, name);
+	return do_id_to_name(rqstp, IDMAP_TYPE_GROUP, id, name);
 }