Merge tag 'nfsd-4.19-1' of git://linux-nfs.org/~bfields/linux

Pull nfsd updates from Bruce Fields:
 "Chuck Lever fixed a problem with NFSv4.0 callbacks over GSS from
  multi-homed servers.

  The only new feature is a minor bit of protocol (change_attr_type)
  which the client doesn't even use yet.

  Other than that, various bugfixes and cleanup"

* tag 'nfsd-4.19-1' of git://linux-nfs.org/~bfields/linux: (27 commits)
  sunrpc: Add comment defining gssd upcall API keywords
  nfsd: Remove callback_cred
  nfsd: Use correct credential for NFSv4.0 callback with GSS
  sunrpc: Extract target name into svc_cred
  sunrpc: Enable the kernel to specify the hostname part of service principals
  sunrpc: Don't use stack buffer with scatterlist
  rpc: remove unneeded variable 'ret' in rdma_listen_handler
  nfsd: use true and false for boolean values
  nfsd: constify write_op[]
  fs/nfsd: Delete invalid assignment statements in nfsd4_decode_exchange_id
  NFSD: Handle full-length symlinks
  NFSD: Refactor the generic write vector fill helper
  svcrdma: Clean up Read chunk path
  svcrdma: Avoid releasing a page in svc_xprt_release()
  nfsd: Mark expected switch fall-through
  sunrpc: remove redundant variables 'checksumlen','blocksize' and 'data'
  nfsd: fix leaked file lock with nfs exported overlayfs
  nfsd: don't advertise a SCSI layout for an unsupported request_queue
  nfsd: fix corrupted reply to badly ordered compound
  nfsd: clarify check_op_ordering
  ...

1 files changed, 34 insertions, 3 deletions

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 0fc397fae42b..962afb8912d5 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;
@@ -456,18 +461,44 @@ static int gss_encode_v1_msg(struct gss_upcall_msg *gss_msg,
 	buflen -= len;
 	p += len;
 	gss_msg->msg.len = len;
+
+	/*
+	 * target= is a full service principal that names the remote
+	 * identity that we are authenticating to.
+	 */
 	if (target_name) {
 		len = scnprintf(p, buflen, "target=%s ", target_name);
 		buflen -= len;
 		p += len;
 		gss_msg->msg.len += len;
 	}
-	if (service_name != NULL) {
-		len = scnprintf(p, buflen, "service=%s ", service_name);
+
+	/*
+	 * gssd uses service= and srchost= to select a matching key from
+	 * the system's keytab to use as the source principal.
+	 *
+	 * service= is the service name part of the source principal,
+	 * or "*" (meaning choose any).
+	 *
+	 * srchost= is the hostname part of the source principal. When
+	 * not provided, gssd uses the local hostname.
+	 */
+	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;
 	}
+
 	if (mech->gm_upcall_enctypes) {
 		len = scnprintf(p, buflen, "enctypes=%s ",
 				mech->gm_upcall_enctypes);