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Commit 8adc6142 authored by Nicholas Bellinger's avatar Nicholas Bellinger Committed by Greg Kroah-Hartman
Browse files

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: default avatarJames Shen <jcs@datera.io>
Cc: James Shen <jcs@datera.io>
Tested-by: default avatarJames Shen <jcs@datera.io>
Signed-off-by: default avatarNicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 4ad69d5f

drivers/target/target_core_fabric_configfs.c

+5 −0
Original line number Diff line number Diff line
@@ -84,6 +84,11 @@ static int target_fabric_mappedlun_link( 
				"_tpg 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_sep->sep_tpg;



	nacl_ci = &lun_acl_ci->ci_parent->ci_group->cg_item;

drivers/target/target_core_tpg.c

+3 −0
Original line number Diff line number Diff line
@@ -843,6 +843,8 @@ void core_tpg_remove_lun( 
	struct se_portal_group *tpg,

	struct se_lun *lun)

{

	lun->lun_shutdown = true;



	core_clear_lun_from_tpg(lun, tpg);

	transport_clear_lun_ref(lun);
@@ -850,6 +852,7 @@ void core_tpg_remove_lun( 


	spin_lock(&tpg->tpg_lun_lock);

	lun->lun_status = TRANSPORT_LUN_STATUS_FREE;

	lun->lun_shutdown = false;

	spin_unlock(&tpg->tpg_lun_lock);



	percpu_ref_exit(&lun->lun_ref);

include/target/target_core_base.h

+1 −0
Original line number Diff line number Diff line
@@ -719,6 +719,7 @@ struct se_lun { 
	u32			lun_access;

	u32			lun_flags;

	u32			unpacked_lun;

	bool			lun_shutdown;

	atomic_t		lun_acl_count;

	spinlock_t		lun_acl_lock;

	spinlock_t		lun_sep_lock;