From mboxrd@z Thu Jan 1 00:00:00 1970 From: wzt wzt Subject: Re: [PATCH] Netfilter: Fix integer overflow in net/ipv6/netfilter/ip6_tables.c Date: Tue, 23 Mar 2010 11:48:06 +0800 Message-ID: <628d1651003222048k1eaf6929r81fd06e401190e0@mail.gmail.com> References: <20100320143240.GB2942@localhost.localdomain> <4BA7A3CF.8070503@trash.net> <628d1651003221834g543e3e6cl4ea39c0886cb4ba1@mail.gmail.com> <7b6bb4a51003221929i16673523nd5f558ccbaace397@mail.gmail.com> <628d1651003221937q58ff39fel467636ab55531128@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Xiaotian Feng , Patrick McHardy , linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org To: Jan Engelhardt Return-path: Received: from mail-yw0-f172.google.com ([209.85.211.172]:65197 "EHLO mail-yw0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754246Ab0CWDsI convert rfc822-to-8bit (ORCPT ); Mon, 22 Mar 2010 23:48:08 -0400 In-Reply-To: Sender: netfilter-devel-owner@vger.kernel.org List-ID: 1=E3=80=81 suppose *len =3D 35, sizeof(struct ipt_get_entries) =3D 36 2=E3=80=81 set get.size =3D 0xffffffff from user space 3=E3=80=81 sizeof(struct ipt_get_entries) + get.size =3D 36 + 0xffffff= ff =3D 35; 4=E3=80=81 if (*len !=3D sizeof(struct ipt_get_entries) + get.size) was= bypassed. you can test with c code: #include int main(void) { unsigned int arg =3D 0xffffffff; printf("%u\n", arg + 36); if (35 !=3D arg + 36) { printf("not over flow.\n"); return -1; } printf("arg over flow.\n"); return 0; } On Tue, Mar 23, 2010 at 11:04 AM, Jan Engelhardt w= rote: > > On Tuesday 2010-03-23 03:37, wzt wzt wrote: >>> And, for the addition overflow, can it be caught by >>> >>> "if (*len !=3D sizeof(struct ipt_get_entries) + get.size)" =C2=A0??= ? >> >>sizeof(struct ipt_get_entries) + get.size can be overflow as *len, >>get.size is control by user space with copy_from_user(). > > The !=3D should catch it. > > For 64-bit environments: > * + invoked with size_t, unsigned int > =C2=A0=3D> right side promoted to size_t, result type is size_t > * !=3D invoked with int and size_t > =C2=A0=3D> left-side promoted to ssize_t (probably; but something as = large as size_t) > * get.size is 32-bit bounded, as is *len, > =C2=A0so no overflow to worry about at all unless you make > =C2=A0sizeof(X) hilariously big close to 2^64 which is rather unlikel= y. > > 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 > =C2=A0represent any value larger than 4294967295. > > > What Was What Was Wanted. > -- To unsubscribe from this list: send the line "unsubscribe netfilter-dev= el" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html