From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E95E9C33CA2 for ; Fri, 10 Jan 2020 13:06:07 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B603F2072A for ; Fri, 10 Jan 2020 13:06:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="BWz+R90z" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B603F2072A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45276 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iptzK-0003K9-S8 for qemu-devel@archiver.kernel.org; Fri, 10 Jan 2020 08:06:06 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:42426) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iptyX-0002hu-RJ for qemu-devel@nongnu.org; Fri, 10 Jan 2020 08:05:19 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iptyU-00036e-S0 for qemu-devel@nongnu.org; Fri, 10 Jan 2020 08:05:16 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:41509 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iptyU-00030f-Mq for qemu-devel@nongnu.org; Fri, 10 Jan 2020 08:05:14 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578661513; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=kgrEt+FvBB/6+IO3osBNiD9sUA4+YSQqtZ9DHhl2xWI=; b=BWz+R90z9bSSi93e7rxuWn7LdTbL3vnghRpsyEHGVu6HvA7veLMtO94yinG4rYNA9gFwxK ldDVADvaRnhj3f83+V7VNWDXAOPkSaloA0IfoRRqkf89kwxHlBAFe6v/YotWf1vp//G11V F1JDRIsq50RASUTaYolynOfyIFLvxv4= 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-232-6azGhjCINbqh8cUKLEtj1g-1; Fri, 10 Jan 2020 08:05:12 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4F008DB23 for ; Fri, 10 Jan 2020 13:05:11 +0000 (UTC) Received: from work-vm (unknown [10.36.118.36]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 90C6F5C1D4; Fri, 10 Jan 2020 13:05:02 +0000 (UTC) Date: Fri, 10 Jan 2020 13:05:00 +0000 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH 032/104] virtiofsd: passthrough_ll: create new files in caller's context Message-ID: <20200110130500.GE3901@work-vm> References: <20191212163904.159893-1-dgilbert@redhat.com> <20191212163904.159893-33-dgilbert@redhat.com> <20200106143011.GK2930416@redhat.com> <20200106190041.GO2798@work-vm> <20200106190843.GP2798@work-vm> <20200107092231.GA3368802@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200107092231.GA3368802@redhat.com> User-Agent: Mutt/1.13.0 (2019-11-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: 6azGhjCINbqh8cUKLEtj1g-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 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: qemu-devel@nongnu.org, stefanha@redhat.com, vgoyal@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Daniel P. Berrang=C3=A9 (berrange@redhat.com) wrote: > On Mon, Jan 06, 2020 at 07:08:43PM +0000, Dr. David Alan Gilbert wrote: > > * Dr. David Alan Gilbert (dgilbert@redhat.com) wrote: > > > * Daniel P. Berrang=C3=A9 (berrange@redhat.com) wrote: > > > > On Thu, Dec 12, 2019 at 04:37:52PM +0000, Dr. David Alan Gilbert (g= it) wrote: > > > > > From: Vivek Goyal > > > > >=20 > > > > > We need to create files in the caller's context. Otherwise after > > > > > creating a file, the caller might not be able to do file operatio= ns on > > > > > that file. > > > > >=20 > > > > > Changed effective uid/gid to caller's uid/gid, create file and th= en > > > > > switch back to uid/gid 0. > > > > >=20 > > > > > Use syscall(setresuid, ...) otherwise glibc does some magic to ch= ange EUID > > > > > in all threads, which is not what we want. > > > > >=20 > > > > > Signed-off-by: Vivek Goyal > > > > > Signed-off-by: Miklos Szeredi > > > > > --- > > > > > tools/virtiofsd/passthrough_ll.c | 79 ++++++++++++++++++++++++++= ++++-- > > > > > 1 file changed, 74 insertions(+), 5 deletions(-) > > > > >=20 > > > > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/p= assthrough_ll.c > > > > > index 68bacb6fc5..0188cd9ad6 100644 > > > > > --- a/tools/virtiofsd/passthrough_ll.c > > > > > +++ b/tools/virtiofsd/passthrough_ll.c > > > >=20 > > > >=20 > > > > > +static int lo_change_cred(fuse_req_t req, struct lo_cred *old) > > > > > +{ > > > > > + int res; > > > > > + > > > > > + old->euid =3D geteuid(); > > > > > + old->egid =3D getegid(); > > > > > + > > > > > + res =3D syscall(SYS_setresgid, -1, fuse_req_ctx(req)->gid, -= 1); > > > >=20 > > > > Do we need to be using SYS_setres[u,g]id32 instead... > > > >=20 > > > > [quote setresgid(2)] > > > > The original Linux setresuid() and setresgid() system calls > > > > supported only 16-bit user and group IDs. Subsequently, > > > > Linux 2.4 added setresuid32() and setresgid32(), supporting > > > > 32-bit IDs. The glibc setresuid() and setresgid() wrapper > > > > functions transparently deal with the variations across ker= =E2=80=90 > > > > nel versions. > > > > [/quote] > > >=20 > > > OK, updated. > >=20 > > Hmm hang on; this is messy. x86-64 only seems to have setresuid > > where as some architectures have both; If I'm reading this right, all > > 64 bit machines have setresuid/gid calling the code that takes the > > 32bit ID; some have compat entries for 32bit syscalls. >=20 > Oh yuk. >=20 > > I think it's probably more correct to call setresuid here; except > > for 32 bit platforms - but how do we tell? >=20 > Is it possible to just do an #ifdef SYS_setresgid32 check to see > if the wider variant exists ? I've ended up with: +/* + * On some archs, setres*id is limited to 2^16 but they + * provide setres*id32 variants that allow 2^32. + * Others just let setres*id do 2^32 anyway. + */ +#ifdef SYS_setresgid32 +#define OURSYS_setresgid SYS_setresgid32 +#else +#define OURSYS_setresgid SYS_setresgid +#endif + +#ifdef SYS_setresuid32 +#define OURSYS_setresuid SYS_setresuid32 +#else +#define OURSYS_setresuid SYS_setresuid +#endif + +/* + * Change to uid/gid of caller so that file is created with + * ownership of caller. + * TODO: What about selinux context? + */ +static int lo_change_cred(fuse_req_t req, struct lo_cred *old) +{ + int res; + + old->euid =3D geteuid(); + old->egid =3D getegid(); + + res =3D syscall(OURSYS_setresgid, -1, fuse_req_ctx(req)->gid, -1); + if (res =3D=3D -1) { + return errno; + } + + res =3D syscall(OURSYS_setresuid, -1, fuse_req_ctx(req)->uid, -1); + if (res =3D=3D -1) { + int errno_save =3D errno; + + syscall(OURSYS_setresgid, -1, old->egid, -1); + return errno_save; + } and in the seccomp: #ifdef __NR_setresgid32 SCMP_SYS(setresgid32), #endif #ifdef __NR_setresuid32 SCMP_SYS(setresuid32), #endif Dave >=20 > Regards, > Daniel > --=20 > |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| > |: https://libvirt.org -o- https://fstop138.berrange.c= om :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK