From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CFB991411EE; Fri, 28 Jun 2024 12:23:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719577422; cv=none; b=OcIE7l4BeVBDxW7dzlemHlozta4h1W+IUfdGm9J+iaF3LZifoueAfFzx4pZO6KhjOEHclrqYm88UL6qGH4FdlUj8tF38yX5bAeDLZ649di5694YXHqROsicWHDtiv/Id758UTjjPyRDMq1iGne0RyIGmCIpPhPOhfn+/IJlThaI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719577422; c=relaxed/simple; bh=tyZqFLkUX46EtxQxpgFqQIPv61XudWLgX6qkok5gyLI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=LGps9e+GQmXbLKCw29H/SZGJL5UWxPySGJmpHmUtuybM02efmTimxd6s2WgfWUzXIsbPGYRs3dJYNRi8hOSPb29felsCNL3QGWtM3HzA5/10F5GpgZY7yaeEyQyRTwNghek1+DcPNIIIMEFtkbKgjfEa7oAhrialvgZVcuM7XKw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=I1vPWRJV; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="I1vPWRJV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F6B7C116B1; Fri, 28 Jun 2024 12:23:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719577421; bh=tyZqFLkUX46EtxQxpgFqQIPv61XudWLgX6qkok5gyLI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=I1vPWRJVMasvY4mSgOwL+L4R0Z01LXE3UFK7pYsVqQdVi4imj1q5a28q9BufwvqyD pCGoelb66a/S5uh8EhKjanRQDQAx6QLWSnS8KqeGrxE2yi5WeWgeThSzaKLvt7h4TN L5RQ7niVHIME7q0U2JSDXX6gtjGaHVAF7EBxt6NyS5W2e+49h33y7ryT2nRhbJDwIJ 1yggZDk953f2jU5O5oNWJQGkZROQETcf+b2Zql9WKFLFAWoq/Mo37IYBvIhGuR8Ppi s5qpC69mAlvQCTXJxNgmDvZMM/9uE92gt+RIMJLAUihUgpq6OB0ccf8aSDgFW9OQDl TSN2daGuoqk3A== Date: Fri, 28 Jun 2024 14:23:35 +0200 From: Christian Brauner To: Jan Kara Cc: Eric Sandeen , linux-fsdevel@vger.kernel.org, autofs@vger.kernel.org, "Rafael J. Wysocki" , linux-efi@vger.kernel.org, Namjae Jeon , linux-ext4@vger.kernel.org, Miklos Szeredi , linux-mm@kvack.org, ntfs3@lists.linux.dev, linux-cifs@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Hans Caniullan Subject: Re: [PATCH 01/14] fs_parse: add uid & gid option option parsing helpers Message-ID: <20240628-fernfahrt-missverstanden-01543e7492b4@brauner> References: <8dca3c11-99f4-446d-a291-35c50ed2dc14@redhat.com> <20240628094517.ifs4bp73nlggsnxz@quack3> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240628094517.ifs4bp73nlggsnxz@quack3> On Fri, Jun 28, 2024 at 11:45:17AM GMT, Jan Kara wrote: > On Thu 27-06-24 19:26:24, Eric Sandeen wrote: > > Multiple filesystems take uid and gid as options, and the code to > > create the ID from an integer and validate it is standard boilerplate > > that can be moved into common helper functions, so do that for > > consistency and less cut&paste. > > > > This also helps avoid the buggy pattern noted by Seth Jenkins at > > https://lore.kernel.org/lkml/CALxfFW4BXhEwxR0Q5LSkg-8Vb4r2MONKCcUCVioehXQKr35eHg@mail.gmail.com/ > > because uid/gid parsing will fail before any assignment in most > > filesystems. > > > > Signed-off-by: Eric Sandeen > > I like the idea since this seems like a nobrainer but is actually > surprisingly subtle... > > > diff --git a/fs/fs_parser.c b/fs/fs_parser.c > > index a4d6ca0b8971..24727ec34e5a 100644 > > --- a/fs/fs_parser.c > > +++ b/fs/fs_parser.c > > @@ -308,6 +308,40 @@ int fs_param_is_fd(struct p_log *log, const struct fs_parameter_spec *p, > > } > > EXPORT_SYMBOL(fs_param_is_fd); > > > > +int fs_param_is_uid(struct p_log *log, const struct fs_parameter_spec *p, > > + struct fs_parameter *param, struct fs_parse_result *result) > > +{ > > + kuid_t uid; > > + > > + if (fs_param_is_u32(log, p, param, result) != 0) > > + return fs_param_bad_value(log, param); > > + > > + uid = make_kuid(current_user_ns(), result->uint_32); > > But here is the problem: Filesystems mountable in user namespaces need to use > fc->user_ns for resolving uids / gids (e.g. like fuse_parse_param()). > Having helpers that work for some filesystems and are subtly broken for > others is worse than no helpers... Or am I missing something? > > And the problem with fc->user_ns is that currently __fs_parse() does not > get fs_context as an argument... So that will need some larger work. Not really. If someone does an fsopen() in a namespace but the process that actually sets mount options is in another namespace then it's completely intransparent what uid/gid this will resolve to if it's resovled according to fsopen(). It's also a bit strange if someone ends up handing off a tmpfs fscontext that was created in the initial namespace to some random namespace and they now can set uid/gid options that aren't mapped according to their namespace but instead are 1:1 resolved according to the intial namespace. So this would hinder delegation. The expectation is that uid/gid options are resolved in the caller's namespace and that shouldn't be any different for fscontexts for namespace mountable filesystems. The crucial point is to ensure that the resulting kuid/kgid can be resolved in the namespace the filesystem is mounted in at the end. That's what was lacking in e.g., tmpfs in commit 0200679fc795 ("tmpfs: verify {g,u}id mount options correctly") The fuse conversion is the only inconsistency in that regard.