linux-kernel - Re: [PATCH net] page_pool: Fix use-after-free in page_pool_recycle_in

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Message-ID: <2c4a2655-2e0d-4c16-82e6-2d9d33d5a276@huawei.com>
Date: Mon, 26 May 2025 22:27:10 +0800
From: "dongchenchen (A)" <dongchenchen2@...wei.com>
To: Yunsheng Lin <linyunsheng@...wei.com>, <hawk@...nel.org>,
	<ilias.apalodimas@...aro.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <horms@...nel.org>,
	<almasrymina@...gle.com>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<zhangchangzhong@...wei.com>,
	<syzbot+204a4382fcb3311f3858@...kaller.appspotmail.com>
Subject: Re: [PATCH net] page_pool: Fix use-after-free in
 page_pool_recycle_in_ring


> On 2025/5/23 14:45, Dong Chenchen wrote:
>
>>   
>>   static bool page_pool_recycle_in_ring(struct page_pool *pool, netmem_ref netmem)
>>   {
>> +	bool in_softirq;
>>   	int ret;
> int -> bool?

Thanks for your review!

v2 will fix it.

>>   	/* BH protection not needed if current is softirq */
>> -	if (in_softirq())
>> -		ret = ptr_ring_produce(&pool->ring, (__force void *)netmem);
>> -	else
>> -		ret = ptr_ring_produce_bh(&pool->ring, (__force void *)netmem);
>> -
>> -	if (!ret) {
>> +	in_softirq = page_pool_producer_lock(pool);
>> +	ret = !__ptr_ring_produce(&pool->ring, (__force void *)netmem);
>> +	if (ret)
>>   		recycle_stat_inc(pool, ring);
>> -		return true;
>> -	}
>> +	page_pool_producer_unlock(pool, in_softirq);
>>   
>> -	return false;
>> +	return ret;
>>   }
>>   
>>   /* Only allow direct recycling in special circumstances, into the
>> @@ -1091,10 +1088,14 @@ static void page_pool_scrub(struct page_pool *pool)
>>   
>>   static int page_pool_release(struct page_pool *pool)
>>   {
>> +	bool in_softirq;
>>   	int inflight;
>>   
>>   	page_pool_scrub(pool);
>>   	inflight = page_pool_inflight(pool, true);
>> +	/* Acquire producer lock to make sure producers have exited. */
>> +	in_softirq = page_pool_producer_lock(pool);
>> +	page_pool_producer_unlock(pool, in_softirq);
> Is a compiler barrier needed to ensure compiler doesn't optimize away
> the above code?

All the code logic of this function accesses the pool. Do we need to
add a compiler barrier for it?

Best Regards,
Dong Chenchen

>>   	if (!inflight)
>>   		__page_pool_destroy(pool);
>>