SUNRPC: Add /proc/net/rpc/gss_krb5_enctypes file

I would like to replace the KRB5_SUPPORTED_ENCTYPES macro so that
there is finer granularity about what enctype support is built in
to the kernel and then advertised by it.

The /proc/fs/nfsd/supported_krb5_enctypes file is a legacy API
that advertises supported enctypes to rpc.svcgssd (I think?). It
simply prints the value of the KRB5_SUPPORTED_ENCTYPES macro, so it
will need to be replaced with something that can instead display
exactly which enctypes are configured and built into the SunRPC
layer.

Completely decommissioning such APIs is hard. Instead, add a file
that is managed by SunRPC's GSS Kerberos mechanism, which is
authoritative about enctype support status. A subsequent patch will
replace /proc/fs/nfsd/supported_krb5_enctypes with a symlink to this
new file.
Tested-by: Scott Mayhew <smayhew@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/auth_gss/svcauth_gss.c

@@ -1494,6 +1494,55 @@ static void destroy_use_gss_proxy_proc_entry(struct net *net)
 		clear_gssp_clnt(sn);
 	}
 }
+
+static ssize_t read_gss_krb5_enctypes(struct file *file, char __user *buf,
+				      size_t count, loff_t *ppos)
+{
+	struct rpcsec_gss_oid oid = {
+		.len	= 9,
+		.data	= "\x2a\x86\x48\x86\xf7\x12\x01\x02\x02",
+	};
+	struct gss_api_mech *mech;
+	ssize_t ret;
+
+	mech = gss_mech_get_by_OID(&oid);
+	if (!mech)
+		return 0;
+	if (!mech->gm_upcall_enctypes) {
+		gss_mech_put(mech);
+		return 0;
+	}
+
+	ret = simple_read_from_buffer(buf, count, ppos,
+				      mech->gm_upcall_enctypes,
+				      strlen(mech->gm_upcall_enctypes));
+	gss_mech_put(mech);
+	return ret;
+}
+
+static const struct proc_ops gss_krb5_enctypes_proc_ops = {
+	.proc_open	= nonseekable_open,
+	.proc_read	= read_gss_krb5_enctypes,
+};
+
+static int create_krb5_enctypes_proc_entry(struct net *net)
+{
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+	if (!proc_create_data("gss_krb5_enctypes", S_IFREG | 0444,
+			      sn->proc_net_rpc,
+			      &gss_krb5_enctypes_proc_ops, net))
+		return -ENOMEM;
+	return 0;
+}
+
+static void destroy_krb5_enctypes_proc_entry(struct net *net)
+{
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+	remove_proc_entry("gss_krb5_enctypes", sn->proc_net_rpc);
+}
+
 #else /* CONFIG_PROC_FS */
 
 static int create_use_gss_proxy_proc_entry(struct net *net)
@@ -1503,6 +1552,13 @@ static int create_use_gss_proxy_proc_entry(struct net *net)
 
 static void destroy_use_gss_proxy_proc_entry(struct net *net) {}
 
+static int create_krb5_enctypes_proc_entry(struct net *net)
+{
+	return 0;
+}
+
+static void destroy_krb5_enctypes_proc_entry(struct net *net) {}
+
 #endif /* CONFIG_PROC_FS */
 
 /*
@@ -2042,7 +2098,15 @@ gss_svc_init_net(struct net *net)
 	rv = create_use_gss_proxy_proc_entry(net);
 	if (rv)
 		goto out2;
+
+	rv = create_krb5_enctypes_proc_entry(net);
+	if (rv)
+		goto out3;
+
 	return 0;
+
+out3:
+	destroy_use_gss_proxy_proc_entry(net);
 out2:
 	rsi_cache_destroy_net(net);
 out1:
@@ -2053,6 +2117,7 @@ gss_svc_init_net(struct net *net)
 void
 gss_svc_shutdown_net(struct net *net)
 {
+	destroy_krb5_enctypes_proc_entry(net);
 	destroy_use_gss_proxy_proc_entry(net);
 	rsi_cache_destroy_net(net);
 	rsc_cache_destroy_net(net);