4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Bellinger <n...@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 <j...@datera.io>
Cc: James Shen <j...@datera.io>
Tested-by: James Shen <j...@datera.io>
Signed-off-by: Nicholas Bellinger <n...@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gre...@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 */


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