Re: [PATCH-next v2] scsi: fix use-after-free problem in scsi_remove_target

[zhongjinghua]

I'm sorry, I sent the wrong email

在 2023/3/6 19:58, Zhong Jinghua 写道:
> 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@xxxxxxxxxx>
> ---
>   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(-)
>
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index e7893835b99a..12e8ed6d55cb 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -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