Device reset thread uses kobject_uevent_env() to get kobj.parent, and it
aces with device init thread which calls device_add() to add kobj.parent
before kobject_uevent_env().
Device init call: Device reset call:
scsi_probe_and_add_lun() scsi_evt_thread()
scsi_add_lun() scsi_evt_emit()
scsi_sysfs_add_sdev() kobject_uevent_env() //get kobj.parent
scsi_target_add() kobject_get_path()
len = get_kobj_path_length () // len=1 because parent hasn't created yet
device_add() // add kobj.parent
kobject_uevent_env()
kobject_get_path() path = kzalloc()
fill_kobj_path() fill_kobj_path() // --length; length -= cur is a negative value
memcpy(path + length, kobject_name(parent), cur); // slab OOB!
Above backtrace describes the problem, device reset thread will get wrong
kobj.parent when device init thread didn’t add kobj.parent yet. When this
racing happened, it triggers the a KASAN dump on the final iteration:
BUG: KASAN: slab-out-of-bounds in kobject_get_path+0xf8/0x1b8
Write of size 11 at addr ffffff80d6bb94f5 by task kworker/3:1/58
<snip>
Call trace:
__kasan_report+0x124/0x1c8
kasan_report+0x54/0x84
kasan_check_range+0x200/0x208
memcpy+0xb8/0xf0
kobject_get_path+0xf8/0x1b8
kobject_uevent_env+0x228/0xa88
scsi_evt_thread+0x2d0/0x5b0
process_one_work+0x570/0xf94
worker_thread+0x7cc/0xf80
kthread+0x2c4/0x388
These two jobs are scheduled asynchronously, we can't guaranteed that
kobj.parent will be created in device init thread before device reset
thread calls kobject_get_path().
To resolve the racing issue between device init thread and device reset
thread, we use wait_event() in scsi_evt_emit() to wait for device_add()
to complete the creation of kobj.parent.
Device init call: Device reset call:
ufshcd_async_scan() scsi_evt_thread()
scsi_scan_host() scsi_evt_emit() <- add wait_event()
do_scsi_scan_host() <- add wake_up()
scsi_scan_host_selected()
scsi_scan_channel()
scsi_probe_and_add_lun()
scsi_target_add()
device_add() // add kobj.parent
kobject_uevent_env()
kobject_get_path()
fill_kobj_path()
do_scan_async() <- wake_up() kobject_uevent_env() // add kobj.parent
kobject_get_path() // get valid kobj.parent
fill_kobj_path()
After we add wake_up at do_scsi_scan_host() in device init thread, we can
ensure that device reset thread will get kobject after device init thread
finishes adding parent.
Signed-off-by: Alice Chao <alice.chao@xxxxxxxxxxxx>
---
Change since v2
-Change commit: Describes the preblem first and then the solution.
-Add commit: Add KASAN error log.
---
drivers/scsi/scsi_lib.c | 1 +
drivers/scsi/scsi_scan.c | 1 +
2 files changed, 2 insertions(+)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 0a70aa763a96..abf9a71ed77c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2461,6 +2461,7 @@ static void scsi_evt_emit(struct scsi_device *sdev, struct scsi_event *evt)
break;
case SDEV_EVT_POWER_ON_RESET_OCCURRED:
envp[idx++] = "SDEV_UA=POWER_ON_RESET_OCCURRED";
+ wait_event(sdev->host->host_wait, sdev->sdev_gendev.kobj.parent != NULL);
break;
default:
/* do nothing */
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index f4e6c68ac99e..431f229ac435 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1904,6 +1904,7 @@ static void do_scsi_scan_host(struct Scsi_Host *shost)
} else {
scsi_scan_host_selected(shost, SCAN_WILD_CARD, SCAN_WILD_CARD,
SCAN_WILD_CARD, 0);
+ wake_up(&shost->host_wait);
}
}
--
2.18.0
