linux-kernel - Re: [PATCH] Netfilter: Fix integer overflow in net/ipv6/netfilter/ip6

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Date:	Tue, 23 Mar 2010 11:05:40 +0800
From:	Xiaotian Feng <xtfeng@...il.com>
To:	wzt wzt <wzt.wzt@...il.com>
Cc:	Patrick McHardy <kaber@...sh.net>, linux-kernel@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH] Netfilter: Fix integer overflow in net/ipv6/netfilter/ip6_tables.c

On Tue, Mar 23, 2010 at 10:37 AM, wzt wzt <wzt.wzt@...il.com> wrote:
>> Patrick's point is that you're using "if (get.size >= INT_MAX /
>> sizeof(struct ipt_get_entries))"
>> So, did you find any chance that get.size * sizeof(struct
>> ipt_get_entries) >= INT_MAX ?
>>
> would you carefully read my explain???
> get.size is copy from the user space,  it can be set as 0x7fffffff,
> addition with sizeof(struct ipt_get_entries) can be overflow.
>

get.size is unsigned int, UINT_MAX is 0x FFFFFFFF, not 0x7FFFFFFF
And you're metioning "addition", then why you're checking as "multiplication"?

>> And, for the addition overflow, can it be caught by
>>
>> "if (*len != sizeof(struct ipt_get_entries) + get.size)"  ???
>>
> sizeof(struct ipt_get_entries) + get.size can be overflow as *len,
> get.size is control by user space with copy_from_user().


>
> On Tue, Mar 23, 2010 at 10:29 AM, Xiaotian Feng <xtfeng@...il.com> wrote:
>> On Tue, Mar 23, 2010 at 9:34 AM, wzt wzt <wzt.wzt@...il.com> wrote:
>>>> I can see that the size might cause an overflow in the addition with
>>>> sizeof(struct ipt_get_entries)
>>> That's the integer overflow i pointed.
>>> get.size is copy from the user space,  it can be set as 0x7fffffff,
>>> addition with sizeof(struct ipt_get_entries) can be overflow.
>>
>> Patrick's point is that you're using "if (get.size >= INT_MAX /
>> sizeof(struct ipt_get_entries))"
>> So, did you find any chance that get.size * sizeof(struct
>> ipt_get_entries) >= INT_MAX ?
>>
>> And, for the addition overflow, can it be caught by
>>
>> "if (*len != sizeof(struct ipt_get_entries) + get.size)"  ???
>>
>>>
>>>        if (*len != sizeof(struct ipt_get_entries) + get.size) {
>>>                duprintf("get_entries: %u != %zu\n",
>>>                         *len, sizeof(get) + get.size);
>>>                return -EINVAL;
>>>        }
>>>
>>> so, check get.size max value before addition with sizeof(struct
>>> ipt_get_entries) to prevent the integer overflow.
>>> --
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>>
>
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