target: Obtain se_node_acl->acl_kref during get_initiator_node_acl

This patch addresses a long standing race where obtaining
se_node_acl->acl_kref in __transport_register_session()
happens a bit too late, and leaves open the potential
for core_tpg_del_initiator_node_acl() to hit a NULL
pointer dereference.

Instead, take ->acl_kref in core_tpg_get_initiator_node_acl()
while se_portal_group->acl_node_mutex is held, and move the
final target_put_nacl() from transport_deregister_session()
into transport_free_session() so that fabric driver login
failure handling using the modern method to still work
as expected.

Also, update core_tpg_get_initiator_node_acl() to take
an extra reference for dynamically generated acls for
demo-mode, before returning to fabric caller.  Also
update iscsi-target sendtargets special case handling
to use target_tpg_has_node_acl() when checking if
demo_mode_discovery == true during discovery lookup.

Note the existing wait_for_completion(&acl->acl_free_comp)
in core_tpg_del_initiator_node_acl() does not change.

Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 41 insertions, 1 deletions

diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 67be44da29ff..3608b1b5ecf7 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -75,9 +75,21 @@ struct se_node_acl *core_tpg_get_initiator_node_acl(
 	unsigned char *initiatorname)
 {
 	struct se_node_acl *acl;
-
+	/*
+	 * Obtain se_node_acl->acl_kref using fabric driver provided
+	 * initiatorname[] during node acl endpoint lookup driven by
+	 * new se_session login.
+	 *
+	 * The reference is held until se_session shutdown -> release
+	 * occurs via fabric driver invoked transport_deregister_session()
+	 * or transport_free_session() code.
+	 */
 	mutex_lock(&tpg->acl_node_mutex);
 	acl = __core_tpg_get_initiator_node_acl(tpg, initiatorname);
+	if (acl) {
+		if (!kref_get_unless_zero(&acl->acl_kref))
+			acl = NULL;
+	}
 	mutex_unlock(&tpg->acl_node_mutex);
 
 	return acl;
@@ -224,6 +236,25 @@ static void target_add_node_acl(struct se_node_acl *acl)
 		acl->initiatorname);
 }
 
+bool target_tpg_has_node_acl(struct se_portal_group *tpg,
+			     const char *initiatorname)
+{
+	struct se_node_acl *acl;
+	bool found = false;
+
+	mutex_lock(&tpg->acl_node_mutex);
+	list_for_each_entry(acl, &tpg->acl_node_list, acl_list) {
+		if (!strcmp(acl->initiatorname, initiatorname)) {
+			found = true;
+			break;
+		}
+	}
+	mutex_unlock(&tpg->acl_node_mutex);
+
+	return found;
+}
+EXPORT_SYMBOL(target_tpg_has_node_acl);
+
 struct se_node_acl *core_tpg_check_initiator_node_acl(
 	struct se_portal_group *tpg,
 	unsigned char *initiatorname)
@@ -240,6 +271,15 @@ struct se_node_acl *core_tpg_check_initiator_node_acl(
 	acl = target_alloc_node_acl(tpg, initiatorname);
 	if (!acl)
 		return NULL;
+	/*
+	 * When allocating a dynamically generated node_acl, go ahead
+	 * and take the extra kref now before returning to the fabric
+	 * driver caller.
+	 *
+	 * Note this reference will be released at session shutdown
+	 * time within transport_free_session() code.
+	 */
+	kref_get(&acl->acl_kref);
 	acl->dynamic_node_acl = 1;
 
 	/*