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>

3 files changed, 55 insertions, 8 deletions

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index a81c0e5ca293..762b2d6ea1cc 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -3435,7 +3435,7 @@ iscsit_build_sendtargets_response(struct iscsi_cmd *cmd,
 
                         if ((tpg->tpg_attrib.generate_node_acls == 0) &&
                             (tpg->tpg_attrib.demo_mode_discovery == 0) &&
-                            (!core_tpg_get_initiator_node_acl(&tpg->tpg_se_tpg,
+                            (!target_tpg_has_node_acl(&tpg->tpg_se_tpg,
                                 cmd->conn->sess->sess_ops->InitiatorName))) {
                                 continue;
                         }
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;
 
         /*
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 7b05ebf8053c..a7c1bb54cf72 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -341,7 +341,6 @@ void __transport_register_session(
                                         &buf[0], PR_REG_ISID_LEN);
                         se_sess->sess_bin_isid = get_unaligned_be64(&buf[0]);
                 }
-                kref_get(&se_nacl->acl_kref);
 
                 spin_lock_irq(&se_nacl->nacl_sess_lock);
                 /*
@@ -432,6 +431,7 @@ void target_put_nacl(struct se_node_acl *nacl)
 {
         kref_put(&nacl->acl_kref, target_complete_nacl);
 }
+EXPORT_SYMBOL(target_put_nacl);
 
 void transport_deregister_session_configfs(struct se_session *se_sess)
 {
@@ -464,6 +464,15 @@ EXPORT_SYMBOL(transport_deregister_session_configfs);
 
 void transport_free_session(struct se_session *se_sess)
 {
+        struct se_node_acl *se_nacl = se_sess->se_node_acl;
+        /*
+         * Drop the se_node_acl->nacl_kref obtained from within
+         * core_tpg_get_initiator_node_acl().
+         */
+        if (se_nacl) {
+                se_sess->se_node_acl = NULL;
+                target_put_nacl(se_nacl);
+        }
         if (se_sess->sess_cmd_map) {
                 percpu_ida_destroy(&se_sess->sess_tag_pool);
                 kvfree(se_sess->sess_cmd_map);
@@ -478,7 +487,7 @@ void transport_deregister_session(struct se_session *se_sess)
         const struct target_core_fabric_ops *se_tfo;
         struct se_node_acl *se_nacl;
         unsigned long flags;
-        bool comp_nacl = true, drop_nacl = false;
+        bool drop_nacl = false;
 
         if (!se_tpg) {
                 transport_free_session(se_sess);
@@ -510,18 +519,16 @@ void transport_deregister_session(struct se_session *se_sess)
         if (drop_nacl) {
                 core_tpg_wait_for_nacl_pr_ref(se_nacl);
                 core_free_device_list_for_node(se_nacl, se_tpg);
+                se_sess->se_node_acl = NULL;
                 kfree(se_nacl);
-                comp_nacl = false;
         }
         pr_debug("TARGET_CORE[%s]: Deregistered fabric_sess\n",
                 se_tpg->se_tpg_tfo->get_fabric_name());
         /*
          * If last kref is dropping now for an explicit NodeACL, awake sleeping
          * ->acl_free_comp caller to wakeup configfs se_node_acl->acl_group
-         * removal context.
+         * removal context from within transport_free_session() code.
          */
-        if (se_nacl && comp_nacl)
-                target_put_nacl(se_nacl);
 
         transport_free_session(se_sess);
 }