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    Subject[PATCH 4.4 12/58] target: Avoid mappedlun symlink creation during lun shutdown
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    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 */

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