linux-kernel - Re: [PATCH] firmware_loader: fix memory leak for paged buffer

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Date:   Fri, 14 Aug 2020 01:21:31 +0530
From:   Prateek Sood <prsood@...eaurora.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     mcgrof@...nel.org, gregkh@...uxfoundation.org, rafael@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firmware_loader: fix memory leak for paged buffer


On 8/13/2020 6:28 PM, Takashi Iwai wrote:
> On Wed, 12 Aug 2020 21:00:19 +0200,
> Prateek Sood wrote:
>> vfree() is being called on paged buffer allocated
>> using alloc_page() and mapped using vmap().
>>
>> Freeing of pages in vfree() relies on nr_pages of
>> struct vm_struct. vmap() does not update nr_pages.
>> It can lead to memory leaks.
>>
>> Signed-off-by: Prateek Sood <prsood@...eaurora.org>
> Thanks for spotting this out!  This is essentially a revert of the
> commit ddaf29fd9bb6 ("firmware: Free temporary page table after
> vmapping"), so better to mention it via Fixes tag as well as Cc to
> stable.
> About the changes:
>> --- a/drivers/base/firmware_loader/firmware.h
>> +++ b/drivers/base/firmware_loader/firmware.h
>> @@ -142,10 +142,12 @@ static inline void fw_state_done(struct fw_priv *fw_priv)
>>   void fw_free_paged_buf(struct fw_priv *fw_priv);
>>   int fw_grow_paged_buf(struct fw_priv *fw_priv, int pages_needed);
>>   int fw_map_paged_buf(struct fw_priv *fw_priv);
>> +bool fw_is_paged_buf(struct fw_priv *fw_priv);
> I guess this isn't necessary if we just swap the call order of
> fw_free_paged_buf() and vfree(); then fw_priv->is_paged_buf is
> referred only in fw_free_paged_buf().
> That is, something like below.
>
> In anyway, take my review tag:
>    Reviewed-by: Takashi Iwai <tiwai@...e.de>

Thanks for reviewing.

I would prefer to keep the patch as is to have vmap() and vunmap() pair used

for readability. Will upload a new version with Fixes tag and your 
Reviewed-by.

>
> thanks,
>
> Takashi
>
> --- a/drivers/base/firmware_loader/main.c
> +++ b/drivers/base/firmware_loader/main.c
> @@ -252,9 +252,9 @@ static void __free_fw_priv(struct kref *ref)
>   	list_del(&fw_priv->list);
>   	spin_unlock(&fwc->lock);
>   
> -	fw_free_paged_buf(fw_priv); /* free leftover pages */
>   	if (!fw_priv->allocated_size)
>   		vfree(fw_priv->data);
> +	fw_free_paged_buf(fw_priv); /* free leftover pages */
>   	kfree_const(fw_priv->fw_name);
>   	kfree(fw_priv);
>   }
> @@ -272,7 +272,7 @@ void fw_free_paged_buf(struct fw_priv *fw_priv)
>   {
>   	int i;
>   
> -	if (!fw_priv->pages)
> +	if (!fw_priv->is_paged_buf)
>   		return;
>   
>   	for (i = 0; i < fw_priv->nr_pages; i++)
> @@ -328,10 +328,6 @@ int fw_map_paged_buf(struct fw_priv *fw_priv)
>   	if (!fw_priv->data)
>   		return -ENOMEM;
>   
> -	/* page table is no longer needed after mapping, let's free */
> -	kvfree(fw_priv->pages);
> -	fw_priv->pages = NULL;
> -
>   	return 0;
>   }
>   #endif

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