From: Zhong Jinghua <zhongjinghua@huawei.com> hulk inclusion category: bugfix bugzilla: 188355, https://gitee.com/openeuler/kernel/issues/I8UF7W ---------------------------------------- A use-after-free problem like below: BUG: KASAN: use-after-free in scsi_target_reap+0x6c/0x70 Workqueue: scsi_wq_1 __iscsi_unbind_session [scsi_transport_iscsi] Call trace: dump_backtrace+0x0/0x320 show_stack+0x24/0x30 dump_stack+0xdc/0x128 print_address_description+0x68/0x278 kasan_report+0x1e4/0x308 __asan_report_load4_noabort+0x30/0x40 scsi_target_reap+0x6c/0x70 scsi_remove_target+0x430/0x640 __iscsi_unbind_session+0x164/0x268 [scsi_transport_iscsi] process_one_work+0x67c/0x1350 worker_thread+0x370/0xf90 kthread+0x2a4/0x320 ret_from_fork+0x10/0x18 The problem is caused by a concurrency scenario: T0: delete target // echo 1 > /sys/devices/platform/host1/session1/target1:0:0/1:0:0:1/delete T1: logout // iscsiadm -m node --logout T0 T1 sdev_store_delete scsi_remove_device device_remove_file __scsi_remove_device __iscsi_unbind_session scsi_remove_target spin_lock_irqsave list_for_each_entry scsi_target_reap // starget->reap_ref 1 -> 0 kref_get(&starget->reap_ref); // warn use-after-free. spin_unlock_irqrestore scsi_target_reap_ref_release scsi_target_destroy ... // delete starget scsi_target_reap // UAF When T0 reduces the reference count to 0, but has not been released, T1 can still enter list_for_each_entry, and then kref_get reports UAF. Fix it by using kref_get_unless_zero() to check for a reference count of 0. Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com> Reviewed-by: Hou Tao <houtao1@huawei.com> Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com> Signed-off-by: Li Nan <linan122@huawei.com> --- drivers/scsi/scsi_sysfs.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index 24f6eefb6803..8fccf2df17f7 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -1584,7 +1584,16 @@ void scsi_remove_target(struct device *dev) starget->state == STARGET_CREATED_REMOVE) continue; if (starget->dev.parent == dev || &starget->dev == dev) { - kref_get(&starget->reap_ref); + /* + * If the reference count is already zero, skip + * this target. Calling kref_get_unless_zero() if + * the reference count is zero is safe because + * scsi_target_destroy() will wait until the host + * lock has been released before freeing starget. + */ + if (!kref_get_unless_zero(&starget->reap_ref)) + continue; + if (starget->state == STARGET_CREATED) starget->state = STARGET_CREATED_REMOVE; else -- 2.39.2