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netfilter-devel: Re: [PATCH] Netfilter: Fix integer overflow in

Re: [PATCH] Netfilter: Fix integer overflow in net/ipv6/netfilter/ip6_tables.c

From: Jan Engelhardt <jengelh_at_nospam>
Date: Tue Mar 23 2010 - 03:04:59 GMT
To: wzt wzt <>

On Tuesday 2010-03-23 03:37, wzt wzt wrote:
>> 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().

The != should catch it.

For 64-bit environments:
* + invoked with size_t, unsigned int
  => right side promoted to size_t, result type is size_t
* != invoked with int and size_t
  => left-side promoted to ssize_t (probably; but something as large as size_t)
* get.size is 32-bit bounded, as is *len,
  so no overflow to worry about at all unless you make
  sizeof(X) hilariously big close to 2^64 which is rather unlikely.

For 32-bit environments:
* Let *len be a number of choice (e.g. 36)
* Find a sizeof(X)+get.size that equals 36 mod 2^32.
* Since sizeof(X) is const, get.size must be 0 mod 2^32.
* So get.size must be a multiple of 2^32 to fool the system.
* Since get.size itself is only a 32-bit quantity, you cannot
  represent any value larger than 4294967295.

What Was What Was Wanted.
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