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

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org> know about it.


>From 49cb77e297dc611a1b795cfeb79452b3002bd331 Mon Sep 17 00:00:00 2001
From: Nicholas Bellinger <nab@linux-iscsi.org>
Date: Mon, 27 Mar 2017 16:12:43 -0700
Subject: target: Avoid mappedlun symlink creation during lun shutdown

From: Nicholas Bellinger <nab@linux-iscsi.org>

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.

Reported-by: James Shen <jcs@datera.io>
Cc: James Shen <jcs@datera.io>
Tested-by: James Shen <jcs@datera.io>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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(+)

--- a/drivers/target/target_core_fabric_configfs.c
+++ b/drivers/target/target_core_fabric_configfs.c
@@ -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;
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -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);
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -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 nab@linux-iscsi.org 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