3.18-stable review patch. If anyone has any objections, please let me know.
------------------ From: Nicholas Bellinger <n...@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 <j...@datera.io> Cc: James Shen <j...@datera.io> Tested-by: James Shen <j...@datera.io> Signed-off-by: Nicholas Bellinger <n...@linux-iscsi.org> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- drivers/target/target_core_fabric_configfs.c | 5 +++++ drivers/target/target_core_tpg.c | 3 +++ include/target/target_core_base.h | 1 + 3 files changed, 9 insertions(+) --- a/drivers/target/target_core_fabric_configfs.c +++ b/drivers/target/target_core_fabric_configfs.c @@ -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; --- a/drivers/target/target_core_tpg.c +++ b/drivers/target/target_core_tpg.c @@ -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); --- a/include/target/target_core_base.h +++ b/include/target/target_core_base.h @@ -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;