sunrpc: Enable the kernel to specify the hostname part of service principals

A multi-homed NFS server may have more than one "nfs" key in its
keytab. Enable the kernel to pick the key it wants as a machine
credential when establishing a GSS context.

This is useful for GSS-protected NFSv4.0 callbacks, which are
required by RFC 7530 S3.3.3 to use the same principal as the service
principal the client used when establishing its lease.

A complementary modification to rpc.gssd is required to fully enable
this feature.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 17 insertions, 3 deletions

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index be8f103d22fd..1943e1198804 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -284,7 +284,12 @@ err:
         return p;
 }
 
-#define UPCALL_BUF_LEN 128
+/* XXX: Need some documentation about why UPCALL_BUF_LEN is so small.
+ *      Is user space expecting no more than UPCALL_BUF_LEN bytes?
+ *      Note that there are now _two_ NI_MAXHOST sized data items
+ *      being passed in this string.
+ */
+#define UPCALL_BUF_LEN  256
 
 struct gss_upcall_msg {
         refcount_t count;
@@ -462,8 +467,17 @@ static int gss_encode_v1_msg(struct gss_upcall_msg *gss_msg,
                 p += len;
                 gss_msg->msg.len += len;
         }
-        if (service_name != NULL) {
-                len = scnprintf(p, buflen, "service=%s ", service_name);
+        if (service_name) {
+                char *c = strchr(service_name, '@');
+
+                if (!c)
+                        len = scnprintf(p, buflen, "service=%s ",
+                                        service_name);
+                else
+                        len = scnprintf(p, buflen,
+                                        "service=%.*s srchost=%s ",
+                                        (int)(c - service_name),
+                                        service_name, c + 1);
                 buflen -= len;
                 p += len;
                 gss_msg->msg.len += len;