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> Cc: stable@vger.kernel.org # 3.10+ Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org> Signed-off-by: Willy Tarreau <w@1wt.eu>
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@ -84,6 +84,11 @@ static int target_fabric_mappedlun_link(
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"_tpg does not exist\n");
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return -EINVAL;
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}
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if (lun->lun_shutdown) {
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pr_err("Unable to create mappedlun symlink because"
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" lun->lun_shutdown=true\n");
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return -EINVAL;
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}
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se_tpg = lun->lun_sep->sep_tpg;
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nacl_ci = &lun_acl_ci->ci_parent->ci_group->cg_item;
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@ -839,6 +839,8 @@ static void core_tpg_shutdown_lun(
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struct se_portal_group *tpg,
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struct se_lun *lun)
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{
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lun->lun_shutdown = true;
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core_clear_lun_from_tpg(lun, tpg);
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transport_clear_lun_from_sessions(lun);
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}
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@ -868,6 +870,7 @@ struct se_lun *core_tpg_pre_dellun(
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spin_unlock(&tpg->tpg_lun_lock);
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return ERR_PTR(-ENODEV);
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}
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lun->lun_shutdown = false;
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spin_unlock(&tpg->tpg_lun_lock);
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return lun;
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@ -729,6 +729,7 @@ struct se_port_stat_grps {
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struct se_lun {
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#define SE_LUN_LINK_MAGIC 0xffff7771
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u32 lun_link_magic;
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bool lun_shutdown;
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/* See transport_lun_status_table */
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enum transport_lun_status_table lun_status;
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u32 lun_access;
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