From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49124) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fn1hk-00035i-5j for qemu-devel@nongnu.org; Tue, 07 Aug 2018 09:07:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fn1hf-0007iZ-Ff for qemu-devel@nongnu.org; Tue, 07 Aug 2018 09:07:16 -0400 References: <20180807114501.12370-1-peter.maydell@linaro.org> <20180807125223.GF2556@work-vm> <20180807125819.GP7335@redhat.com> From: Thomas Huth Message-ID: <00ac9577-52cc-bf48-f0b8-7d15abb2c21f@redhat.com> Date: Tue, 7 Aug 2018 15:07:07 +0200 MIME-Version: 1.0 In-Reply-To: <20180807125819.GP7335@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH for-3.0] slirp: Correct size check in m_inc() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" , "Dr. David Alan Gilbert" Cc: Peter Maydell , Prasad J Pandit , patches@linaro.org, Jan Kiszka , jasowang@redhat.com, qemu-devel@nongnu.org, liqsub1 , Samuel Thibault , qemu-stable@nongnu.org On 08/07/2018 02:58 PM, Daniel P. Berrang=C3=A9 wrote: > On Tue, Aug 07, 2018 at 01:52:24PM +0100, Dr. David Alan Gilbert wrote: >> * Peter Maydell (peter.maydell@linaro.org) wrote: >>> The data in an mbuf buffer is not necessarily at the start of the >>> allocated buffer. (For instance m_adj() allows data to be trimmed >>> from the start by just advancing the pointer and reducing the length.= ) >>> This means that the allocated buffer size (m->m_size) and the >>> amount of space from the m_data pointer to the end of the >>> buffer (M_ROOM(m)) are not necessarily the same. >>> >>> Commit 864036e251f54c9 tried to change the m_inc() function from >>> taking the new allocated-buffer-size to taking the new room-size, >>> but forgot to change the initial "do we already have enough space" >>> check. This meant that if we were trying to extend a buffer which >>> had a leading gap between the buffer start and the data, we might >>> incorrectly decide it didn't need to be extended, and then >>> overrun the end of the buffer, causing memory corruption and >>> an eventual crash. >>> >>> Change the "already big enough?" condition from checking the >>> argument against m->m_size to checking against M_ROOM(). >>> This only makes a difference for the callsite in m_cat(); >>> the other three callsites all start with a freshly allocated >>> mbuf from m_get(), which will have m->m_size =3D=3D M_ROOM(m). >>> >>> Fixes: 864036e251f54c9 >=20 > IIUC, this changeset was a security fix for CVE-2018-11806. >=20 > Given that the fix was flawed and allowed guest to crash the host > with a new buffer overrun, it seems we need to get a new CVE allocated > too. But 864036e251f54c9 was never part of an official QEMU release, was it? Or did it go into a stable release already? If not, I think you simply need both patches to fix the CVE instead. Thomas