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bh=NrJRw/GQsmp4QSSde9KHxk64U090O1fjmeDUzZpM+P8=; b=GIGqOTYPy0tUMbgDYNsqma8GWhBpZIZZE7+Z6yT7ahl1aAzofc+/qUkEM1GgfbbE1T0NDD eL3WC7ELb72UfQSpI56m08y8uvktUwfu/YIWkSOEACi6exHMR/Lg/yJLXLBxFeA57I8KJu XOJ6wK/njy2RX+wAVn0HDjUWobFe/4s= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-487-LS88h7ByPOOIcyeQMs3kkA-1; Thu, 04 Feb 2021 04:47:46 -0500 X-MC-Unique: LS88h7ByPOOIcyeQMs3kkA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E72DD100AA2B; Thu, 4 Feb 2021 09:47:44 +0000 (UTC) Received: from localhost (ovpn-115-89.ams2.redhat.com [10.36.115.89]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4E51B5D9C0; Thu, 4 Feb 2021 09:47:35 +0000 (UTC) Date: Thu, 4 Feb 2021 09:47:34 +0000 From: Stefan Hajnoczi To: Vivek Goyal Subject: Re: [PATCH v4 3/3] virtiofsd: prevent opening of special files (CVE-2020-35517) Message-ID: <20210204094734.GC344659@stefanha-x1.localdomain> References: <20210203113719.83633-1-stefanha@redhat.com> <20210203113719.83633-4-stefanha@redhat.com> <20210203152850.GA3307@redhat.com> <20210203170237.0c98f95f@bahia.lan> <20210203160858.GC3307@redhat.com> <20210203170514.GL74271@stefanha-x1.localdomain> <20210203211441.GH3307@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210203211441.GH3307@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="bKyqfOwhbdpXa4YI" Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.539, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mszeredi@redhat.com, Daniel Berrange , slp@redhat.com, qemu-devel@nongnu.org, Greg Kurz , "Dr. David Alan Gilbert" , virtio-fs@redhat.com, Alex Xu , P J P , Laszlo Ersek Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --bKyqfOwhbdpXa4YI Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Feb 03, 2021 at 04:14:41PM -0500, Vivek Goyal wrote: > On Wed, Feb 03, 2021 at 05:05:14PM +0000, Stefan Hajnoczi wrote: > > On Wed, Feb 03, 2021 at 11:08:58AM -0500, Vivek Goyal wrote: > > > On Wed, Feb 03, 2021 at 05:02:37PM +0100, Greg Kurz wrote: > > > > On Wed, 3 Feb 2021 10:28:50 -0500 > > > > Vivek Goyal wrote: > > > >=20 > > > > > On Wed, Feb 03, 2021 at 11:37:19AM +0000, Stefan Hajnoczi wrote: > > > > >=20 > > > > > [..] > > > > > > @@ -1727,36 +1764,38 @@ static void lo_create(fuse_req_t req, f= use_ino_t parent, const char *name, > > > > > > =20 > > > > > > update_open_flags(lo->writeback, lo->allow_direct_io, fi); > > > > > > =20 > > > > > > - fd =3D openat(parent_inode->fd, name, (fi->flags | O_CREAT= ) & ~O_NOFOLLOW, > > > > > > - mode); > > > > > > + /* Try to create a new file but don't open existing files = */ > > > > > > + fd =3D openat(parent_inode->fd, name, fi->flags | O_CREAT = | O_EXCL, mode); > > > > > > err =3D fd =3D=3D -1 ? errno : 0; > > > > > > + > > > > > > lo_restore_cred(&old); > > > > > > =20 > > > > > > - if (!err) { > > > > > > - ssize_t fh; > > > > > > - > > > > > > - pthread_mutex_lock(&lo->mutex); > > > > > > - fh =3D lo_add_fd_mapping(lo, fd); > > > > > > - pthread_mutex_unlock(&lo->mutex); > > > > > > - if (fh =3D=3D -1) { > > > > > > - close(fd); > > > > > > - err =3D ENOMEM; > > > > > > - goto out; > > > > > > - } > > > > > > + /* Ignore the error if file exists and O_EXCL was not give= n */ > > > > > > + if (err && !(err =3D=3D EEXIST && !(fi->flags & O_EXCL))) = { > > > > >=20 > > > > > Can this check be simplified to. > > > > > if (err && (err =3D=3D EEXIST && (fi->flags & O_EXCL)) { > > > >=20 > > > > I guess you meant : > > > >=20 > > > > if (err && (err !=3D EEXIST || fi->flags & O_EXCL) { > > >=20 > > > This sounds correct. I forgot to take into account that if error is > > > not -EEXIST, we still want to bail out irrespective of O_EXCL. > >=20 > > I thought about De Morgan's law too but found the OR expression is not > > easier to read than the AND expression :(. If you prefer it written thi= s > > way I can change it though. >=20 > I personally find this one to read. And not because of AND but because > of double logical negation (!x) in previous expression. >=20 > But I am not particular about it. If you don't find it easier to > read, I can live with previous one. Okay, I'll convert it. Dave also mentioned he finds the AND version strange. 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