netdev - Re: [PATCH] tcp: use kmalloc() than kmalloc

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Message-Id: <201511080058.FBI87526.FLOVOtFHJMQSOF@I-love.SAKURA.ne.jp>
Date:	Sun, 8 Nov 2015 00:58:50 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	edumazet@...gle.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: use kmalloc() than kmalloc_array().

Tetsuo Handa wrote:
> Commit 095dc8e0c3686d58 ("tcp: fix/cleanup inet_ehash_locks_alloc()")
> silently changed from kmalloc() to kmalloc_array(). The latter has
> overflow check whereas the former doesn't have.
> 
> If nblocks * locksz might overflow, we need to do like
> 
>   -  if (!hashinfo->ehash_locks && nblocks > SIZE_MAX / locksz)
>   +  if (!hashinfo->ehash_locks && nblocks > SIZE_MAX / locksz)

Oops, I meant

   -  if (!hashinfo->ehash_locks)
   +  if (!hashinfo->ehash_locks && nblocks > SIZE_MAX / locksz)

here.

>        hashinfo->ehash_locks = vmalloc(nblocks * locksz);
> 
> because kmalloc_array() detects overflow and returns NULL.
> But if nblocks * locksz is guaranteed not to overflow, there is
> no need to use kmalloc_array().
> 
> Since I assume it won't overflow, use kmalloc() than kmalloc_array().

I don't know about possible value range.
Please confirm that it can't overflow.
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