linux-kernel - Re: [PATCH v1] devres: Fix devm_krealloc() allocating memory with wrong size

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Message-ID: <4f691c9c-8882-4bd7-ba60-3fc665d0808c@quicinc.com>
Date: Sun, 16 Jun 2024 18:10:02 +0800
From: quic_zijuhu <quic_zijuhu@...cinc.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: <rafael@...nel.org>, <andriy.shevchenko@...ux.intel.com>, <brgl@...ev.pl>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] devres: Fix devm_krealloc() allocating memory with
 wrong size

On 6/16/2024 6:02 PM, Greg KH wrote:
> On Sun, Jun 16, 2024 at 05:54:15PM +0800, Zijun Hu wrote:
>> Kernel API devm_krealloc() calls alloc_dr() with wrong argument
>> @total_new_size, and it will cause more memory to be allocated
>> than required, fixed by using @new_size as alloc_dr()'s argument.
>>
>> Fixes: f82485722e5d ("devres: provide devm_krealloc()")
>> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
>> ---
>>  drivers/base/devres.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/base/devres.c b/drivers/base/devres.c
>> index 3df0025d12aa..1cf87ddf1f55 100644
>> --- a/drivers/base/devres.c
>> +++ b/drivers/base/devres.c
>> @@ -898,7 +898,7 @@ void *devm_krealloc(struct device *dev, void *ptr, size_t new_size, gfp_t gfp)
>>  	 * taking the lock as most probably the caller uses GFP_KERNEL.
>>  	 */
>>  	new_dr = alloc_dr(devm_kmalloc_release,
>> -			  total_new_size, gfp, dev_to_node(dev));
>> +			  new_size, gfp, dev_to_node(dev));
> 
> Wait, are you sure?  Did you properly test this?  What is the actual
> savings and how do you handle the fact that you are now not allocating
> the space reserved for the devres structure itself?
> 
sure even if i did not test it.
beware that alloc_dr() will call check_dr_size() to reserve space for
devres structure.

it will reserve the devres structure two times if using wrong
@total_new_size. it is obvious wrong.

> thanks,
> 
> greg k-h