linux-kernel - Re: [PATCH 2/2] padata: fix UAF in padata

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Message-ID: <dc4a4fc1-2628-4e0c-8b8e-1e44193c440e@huaweicloud.com>
Date: Tue, 10 Dec 2024 17:38:51 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: chenridong <chenridong@...wei.com>,
 Daniel Jordan <daniel.m.jordan@...cle.com>
Cc: steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
 linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
 wangweiyang2@...wei.com
Subject: Re: [PATCH 2/2] padata: fix UAF in padata_reorder



On 2024/12/6 11:48, chenridong wrote:
> 
> 
> On 2024/12/6 7:01, Daniel Jordan wrote:
>> Hello Ridong,
>>
>> On Sat, Nov 23, 2024 at 08:05:09AM +0000, Chen Ridong wrote:
>>> From: Chen Ridong <chenridong@...wei.com>
>>>
>>> A bug was found when run ltp test:
>> ...snip...
>>> This can be explained as bellow:
>>>
>>> pcrypt_aead_encrypt
>>> ...
>>> padata_do_parallel
>>> refcount_inc(&pd->refcnt); // add refcnt
>>> ...
>>> padata_do_serial
>>> padata_reorder // pd
>>> while (1) {
>>> padata_find_next(pd, true); // using pd
>>> queue_work_on
>>> ...
>>> padata_serial_worker				crypto_del_alg
>>> padata_put_pd_cnt // sub refcnt
>>> 						padata_free_shell
>>> 						padata_put_pd(ps->pd);
>>> 						// pd is freed
>>> // loop again, but pd is freed
>>> // call padata_find_next, UAF
>>> }
>>
>> Thanks for the fix and clear explanation.
>>
>>> diff --git a/kernel/padata.c b/kernel/padata.c
>>> index 5d8e18cdcb25..627014825266 100644
>>> --- a/kernel/padata.c
>>> +++ b/kernel/padata.c
>>> @@ -319,6 +319,7 @@ static void padata_reorder(struct parallel_data *pd)
>>>  	if (!spin_trylock_bh(&pd->lock))
>>>  		return;
>>>  
>>> +	padata_get_pd(pd);
>>>  	while (1) {
>>>  		padata = padata_find_next(pd, true);
>>>  
>>> @@ -355,6 +356,7 @@ static void padata_reorder(struct parallel_data *pd)
>>>  	reorder = per_cpu_ptr(pd->reorder_list, pd->cpu);
>>>  	if (!list_empty(&reorder->list) && padata_find_next(pd, false))
>>>  		queue_work(pinst->serial_wq, &pd->reorder_work);
>>> +	padata_put_pd(pd);
>>
>> Putting the ref unconditionally here doesn't cover the case where reorder_work
>> is queued and accesses the freed pd.
>>
>> The review of patches 3-5 from this series has a potential solution for
>> this that also keeps some of these refcount operations out of the fast
>> path:
>>
>>     https://lore.kernel.org/all/20221019083708.27138-1-nstange@suse.de/
>>
> 
> Thank you for your review.
> 
> IIUC, patches 3-5 from this series aim to fix two issue.
> 1. Avoid UAF for pd(the patch 3).
> 2. Avoid UAF for ps(the patch 4-5).
> What my patch 2 intends to fix is the issue 1.
> 
> Let's focus on issue 1.
> As shown bellow, if reorder_work is queued, the refcnt must greater than
> 0, since its serial work have not be finished yet. Do your agree with that?
> 
> pcrypt_aead_encrypt/pcrypt_aead_decrypt
> padata_do_parallel 			// refcount_inc(&pd->refcnt);
> padata_parallel_worker	
> padata->parallel(padata);
> padata_do_serial(padata);		
> // pd->reorder_list 			// enque reorder_list
> padata_reorder
>  - case1:squeue->work
> 	padata_serial_worker		// sub refcnt cnt
>  - case2:pd->reorder_work		// reorder->list is not empty
> 	invoke_padata_reorder 		// this means refcnt > 0
> 	...
> 	padata_serial_worker
> 
> I think the patch 3(from Nicolai Stange) can also avoid UAF for pd, but
> it's complicated. IIUC, the issue 1 can only occur in the scenario what
> I mentioned is my commit message. How I fix issue 1 is by adding and
> putting the refcnt in the padata_reorder function, which is simple and
> clear.
> 
> If understand something uncorrectly, please let me know.
> 
> As the issue 2, I have not encountered it, but it exists in theory.
> 
> Thanks,
> Ridong

Hi, Daniel, I am trying to produce the issue 2. However，I failed.
I added 'mdelay' as helper.

 static void padata_reorder(struct parallel_data *pd)
 {
+       mdelay(10);
        struct padata_instance *pinst = pd->ps->pinst;
        int cb_cpu;
        struct padata_priv *padata;

I believe this can increase the probability of issue 2. But after
testing with pcrypt_aead01, issue 2 cannot be reproduced.
And I don't know whether it exists now.

Looking forward your reply.

Best regards,
Ridong