linux-kernel - Re: [PATCH-next] scsi: fix use-after-free problem in scsi_remove

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Date:   Wed, 1 Mar 2023 11:40:02 +0800
From:   zhongjinghua <zhongjinghua@...weicloud.com>
To:     zhongjinghua <zhongjinghua@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH-next] scsi: fix use-after-free problem in
 scsi_remove_target

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@...wei.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@...wei.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;
>> +            }
>> +
>>               if (starget->state == STARGET_CREATED)
>>                   starget->state = STARGET_CREATED_REMOVE;
>>               else