linux-kernel - RE: [PATCH v3 2/2] igb: Proactively round up to kmalloc bucket size

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Date:   Mon, 31 Oct 2022 20:42:36 +0000
From:   "Ruhl, Michael J" <michael.j.ruhl@...el.com>
To:     Kees Cook <keescook@...omium.org>
CC:     "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: RE: [PATCH v3 2/2] igb: Proactively round up to kmalloc bucket size

>-----Original Message-----
>From: Kees Cook <keescook@...omium.org>
>Sent: Friday, October 28, 2022 11:18 PM
>To: Ruhl, Michael J <michael.j.ruhl@...el.com>
>Cc: Brandeburg, Jesse <jesse.brandeburg@...el.com>; Nguyen, Anthony L
><anthony.l.nguyen@...el.com>; David S. Miller <davem@...emloft.net>;
>Eric Dumazet <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>;
>Paolo Abeni <pabeni@...hat.com>; intel-wired-lan@...ts.osuosl.org;
>netdev@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
>hardening@...r.kernel.org
>Subject: Re: [PATCH v3 2/2] igb: Proactively round up to kmalloc bucket size
>
>On Tue, Oct 18, 2022 at 02:25:25AM -0700, Kees Cook wrote:
>> In preparation for removing the "silently change allocation size"
>> users of ksize(), explicitly round up all q_vector allocations so that
>> allocations can be correctly compared to ksize().
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>
>Hi! Any feedback on this part of the patch pair?
>
>> ---
>>  drivers/net/ethernet/intel/igb/igb_main.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c
>b/drivers/net/ethernet/intel/igb/igb_main.c
>> index 6256855d0f62..7a3a41dc0276 100644
>> --- a/drivers/net/ethernet/intel/igb/igb_main.c
>> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
>> @@ -1195,7 +1195,7 @@ static int igb_alloc_q_vector(struct igb_adapter
>*adapter,
>>  		return -ENOMEM;
>>
>>  	ring_count = txr_count + rxr_count;
>> -	size = struct_size(q_vector, ring, ring_count);
>> +	size = kmalloc_size_roundup(struct_size(q_vector, ring, ring_count));
>>
>>  	/* allocate q_vector and rings */
>>  	q_vector = adapter->q_vector[v_idx];

Hi Kees,

Looking at the size usage (from elixir), I see:

--
	if (!q_vector) {
		q_vector = kzalloc(size, GFP_KERNEL);
	} else if (size > ksize(q_vector)) {
		kfree_rcu(q_vector, rcu);
		q_vector = kzalloc(size, GFP_KERNEL);
	} else {
		memset(q_vector, 0, size);
	}
--

If the size is rounded up, will the (size > ksize()) check ever be true?

I.e. have you eliminated this check (and maybe getting rid of the need for first patch?)?

Thanks,

Mike


>
>Thanks! :)
>
>-Kees
>
>--
>Kees Cook