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

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Date:	Tue, 23 Mar 2010 10:37:06 +0800
From:	wzt wzt <wzt.wzt@...il.com>
To:	Xiaotian Feng <xtfeng@...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

> 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.

> 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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