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

[zhongjinghua <zhongjinghua@huawei.com>]

在 2023/3/2 3:51, James Bottomley 写道:
> On Wed, 2023-03-01 at 11:40 +0800, zhongjinghua wrote:
>> ping...
>>
>> Hello，
>>
>> Anyone looking this？
>>
>> 在 2023/3/1 11:37, zhongjinghua 写道:
>>> ping...
>>>
>>> Hello，
>>>
>>> Anyone looking this？
>>>
>>> 在 2023/2/13 11:43, Zhong Jinghua 写道:
>>>> From: Zhong Jinghua <zhongjinghua@huawei.com>
>>>>
>>>> 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->reaf 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>
>>>> ---
>>>>    drivers/scsi/scsi_sysfs.c | 12 +++++++++++-
>>>>    1 file changed, 11 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/scsi/scsi_sysfs.c
>>>> b/drivers/scsi/scsi_sysfs.c
>>>> index e7893835b99a..0ad357ff4c59 100644
>>>> --- a/drivers/scsi/scsi_sysfs.c
>>>> +++ b/drivers/scsi/scsi_sysfs.c
>>>> @@ -1561,7 +1561,17 @@ 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 starget->reap_ref is reduced to 0, it means
>>>> +             * that other processes are releasing it and
>>>> +             * there is no need to delete it again
>>>> +             */
>>>> +            if (!kref_get_unless_zero(&starget->reap_ref)) {
>>>> +                spin_unlock_irqrestore(shost->host_lock, flags);
>>>> +                goto restart;
> This doesn't seem to be a good idea: you're asking for a live lock
> where the thread that's already reduced the refcount to 0 and will
> eventually remove the target from the list doesn't progress before you
> take the lock again in the restart and then you find the same result
> and go round again (and again ...).

I agree with this, no need to use goto restart.

> Since there should only be one match in the target list and you found
> it and know it's going away, what about break instead of unlock and
> goto restart?

Wouldn't it be better to use continue? Assuming that the device 
parameter is a session, maybe not only one is matched.

>
> James

Thanks.

Jinghua.