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target: Avoid mappedlun symlink creation during lun shutdown

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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>
This commit is contained in:
Nicholas Bellinger 2017-03-27 16:12:43 -07:00
parent efb2ea770b
commit 49cb77e297
3 changed files with 10 additions and 0 deletions
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5
drivers/target/target_core_fabric_configfs.c
View File

@ -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;

4
drivers/target/target_core_tpg.c
View File

@ -642,6 +642,8 @@ 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
@ -663,6 +665,8 @@ 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);

1
include/target/target_core_base.h
View File

@ -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;