@@ -1561,7 +1561,16 @@ 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 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
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> --- v2: commit message: "starget->reaf" -> "starget->reap_ref" comment: "If it is reduced to 0, it means that other processes are releasing it and there is no need to delete it again" -> "If the reference count is already zero, skip this target is safe because scsi_target_destroy() will wait until the host lock has been released before freeing starget." drivers/scsi/scsi_sysfs.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)