linux-kernel - Re: [PATCH] params: fix potential memory leak in add_sysfs

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Message-ID: <CAJFMrCG1OXrdRoUNqtZYdBqE_0dj+a3yAfFhuyFvTte7Ozbo0w@mail.gmail.com>
Date:	Thu, 21 Aug 2014 02:38:19 +0530
From:	Arjun Sreedharan <arjun024@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jingoo Han <jg1.han@...sung.com>, linux-kernel@...r.kernel.org,
	David Woodhouse <David.Woodhouse@...el.com>
Subject: Re: [PATCH] params: fix potential memory leak in add_sysfs_param()

On 21 August 2014 02:19, Rusty Russell <rusty@...tcorp.com.au> wrote:
> Arjun Sreedharan <arjun024@...il.com> writes:
>> Do not leak memory when attrs is non NULL and
>> krealloc() fails. Without temporary variable,
>> reference to it is lost.
>>
>> Signed-off-by: Arjun Sreedharan <arjun024@...il.com>
>
> ...
>
>>       }
>> -     /* Despite looking like the typical realloc() bug, this is safe.
>> -      * We *want* the old 'attrs' to be freed either way, and we'll store
>> -      * the new one in the success case. */
>> -     attrs = krealloc(attrs, sizeof(new->grp.attrs[0])*(num+2), GFP_KERNEL);
>> -     if (!attrs) {
>> +
>> +     new_attrs = krealloc(attrs, sizeof(new->grp.attrs[0])*(num+2), GFP_KERNEL);
>> +     if (!new_attrs) {
>
> I think that comment you deleted is pretty clear.  Is it wrong?
>
> Cheers,
> Rusty.

I believe it's wrong. I do not understand how `this is safe` from memory leak.
If krealloc() fails, there is nothing in place to free memory held by @attrs
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