target: Avoid mappedlun symlink creation during lun shutdown

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>

3 files changed, 10 insertions, 0 deletions

diff --git a/drivers/target/target_core_fabric_configfs.c b/drivers/target/target_core_fabric_configfs.c
index 31a096aa16ab..6e456de5e564 100644
--- 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;
diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 2744251178ad..1949f50725a5 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -640,6 +640,8 @@ 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
@@ -661,6 +663,8 @@ 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);
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 6233e8fd95b5..0383c601e17c 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -705,6 +705,7 @@ struct se_lun {
         u64                     unpacked_lun;
 #define SE_LUN_LINK_MAGIC                       0xffff7771
         u32                     lun_link_magic;
+        bool                    lun_shutdown;
         bool                    lun_access_ro;
         u32                     lun_index;