Patch "target: Avoid mappedlun symlink creation during lun shutdown" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

target: Avoid mappedlun symlink creation during lun shutdown

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
target-avoid-mappedlun-symlink-creation-during-lun-shutdown.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Nicholas Bellinger <[email protected]>
Date: Mon, 27 Mar 2017 16:12:43 -0700
Subject: target: Avoid mappedlun symlink creation during lun shutdown

From: Nicholas Bellinger <[email protected]>

commit 49cb77e297dc611a1b795cfeb79452b3002bd331 upstream.

This patch closes a race between se_lun deletion during configfs unlink in target_fabric_port_unlink() -> core_dev_del_lun() -> core_tpg_remove_lun(), when transport_clear_lun_ref() blocks waiting for percpu_ref RCU grace period to finish, but a new NodeACL mappedlun is added before the RCU grace period has completed.

This can happen in target_fabric_mappedlun_link() because it only checks for se_lun->lun_se_dev, which is not cleared until after transport_clear_lun_ref() percpu_ref RCU grace period finishes.

This bug originally manifested as NULL pointer dereference OOPsen in target_stat_scsi_att_intr_port_show_attr_dev() on v4.1.y code, because it dereferences lun->lun_se_dev without a explicit NULL pointer check.

In post v4.1 code with target-core RCU conversion, the code in target_stat_scsi_att_intr_port_show_attr_dev() no longer uses se_lun->lun_se_dev, but the same race still exists.

To address the bug, go ahead and set se_lun>lun_shutdown as early as possible in core_tpg_remove_lun(), and ensure new NodeACL mappedlun creation in target_fabric_mappedlun_link() fails during se_lun shutdown.

---
 drivers/target/target_core_fabric_configfs.c |    5 +++++
 drivers/target/target_core_tpg.c             |    4 ++++
 include/target/target_core_base.h            |    1 +
 3 files changed, 10 insertions(+)

@@ -92,6 +92,11 @@ static int target_fabric_mappedlun_link(
 		pr_err("Source se_lun->lun_se_dev does not exist\n");
 		return -EINVAL;
 	}
+	if (lun->lun_shutdown) {
+		pr_err("Unable to create mappedlun symlink because"
+			" lun->lun_shutdown=true\n");
+		return -EINVAL;
+	}
 	se_tpg = lun->lun_tpg;
 
 	nacl_ci = &lun_acl_ci->ci_parent->ci_group->cg_item;

@@ -673,6 +673,8 @@ void core_tpg_remove_lun(
 	 */
 	struct se_device *dev = rcu_dereference_raw(lun->lun_se_dev);
 
+	lun->lun_shutdown = true;
+
 	core_clear_lun_from_tpg(lun, tpg);
 	/*
 	 * Wait for any active I/O references to percpu se_lun->lun_ref to

@@ -694,6 +696,8 @@ void core_tpg_remove_lun(
 	}
 	if (!(dev->se_hba->hba_flags & HBA_FLAGS_INTERNAL_USE))
 		hlist_del_rcu(&lun->link);
+
+	lun->lun_shutdown = false;
 	mutex_unlock(&tpg->tpg_lun_mutex);
 
 	percpu_ref_exit(&lun->lun_ref);

@@ -714,6 +714,7 @@ struct se_lun {
 #define SE_LUN_LINK_MAGIC			0xffff7771
 	u32			lun_link_magic;
 	u32			lun_access;
+	bool			lun_shutdown;
 	u32			lun_index;
 
 	/* RELATIVE TARGET PORT IDENTIFER */

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/iscsi-target-fix-delayed-logout-processing-greater-than-seconds_for_logout_comp.patch queue-4.4/iscsi-target-always-wait-for-kthread_should_stop-before-kthread-exit.patch queue-4.4/iscsi-target-fix-early-sk_data_ready-login_flags_ready-race.patch queue-4.4/iscsi-target-fix-initial-login-pdu-asynchronous-socket-close-oops.patch queue-4.4/iser-target-avoid-isert_conn-cm_id-dereference-in-isert_login_recv_done.patch queue-4.4/target-avoid-mappedlun-symlink-creation-during-lun-shutdown.patch