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 4CFB41DE4CD; Tue, 3 Feb 2026 16:21:28 +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=1770135688; cv=none; b=dF2TrKhphuGQgymrohLIglWgZQGvSyQ96HTCVOnbU1WkxXgpm/l8RHfgdiK3dJhcWPVjTX3NKTobBY+frHDvHt9WxSRjKqfXYuc1UBGnsHzaSjaVmysh/9ytGNJ4LU1fgwXBmPL/xdYG3WaIE6O9beHm4rrRmtPJn0U8xhOZseU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770135688; c=relaxed/simple; bh=XA4BpqiS0cObmCsHqyZeNBqWrIQ2ztNVJvmfQBq/m00=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=KaoAwfa1bwDEby2Zv5HtywYikqEcx4nCWq8DbpsJEtHXhq7WlxbDorDzHF7pdxN1zyUFGuhN0yV4IUmvg2wvJtI5UGGTLOrxhZT5wWNmUvl4TmF6wb+is4a4Zvn7eI5b+QUoMCwRAL2Q0pdOdlMs80UbCZ1YdAlGB3ccS9gN6hA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ozZhOGeL; 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="ozZhOGeL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA958C116D0; Tue, 3 Feb 2026 16:21:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770135687; bh=XA4BpqiS0cObmCsHqyZeNBqWrIQ2ztNVJvmfQBq/m00=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ozZhOGeLiWCo8YXiAe08dxLWwlODXEYBnEFP7hB5bE+dB02fIfcqvxQHZnLBGMdl+ O55OQiIjc+UXBk8rD4N/dmdYewz9XohSaxljxZlrM9LWVqfbTNZDg30kjWCBLPKqhs /XDCwFbgBORPcENiWk1O+4IVeCAS0ip/UC3vUQ92tukHgNCjD4fdn3zyV/pUo4K/Zl VBCwm+AhLEZn3hgEwAuOTD6DS39fYHkeEKlRJT+Y7SFZxb62kcIG7xwB8+dr90kkPk ocKATrcQzm2pPFivfRpXfnmi7zq10A6zSYQHj4OrVhTXnPD/jiFZuSW9KSHoFdgFJP lFsXTfS26uXaQ== Message-ID: <6dd181bf9f6371339a6c31f58f582a9aac3bc36a.camel@kernel.org> Subject: Re: [PATCH] vfs: add FS_USERNS_DELEGATABLE flag and set it for NFS From: Jeff Layton To: Alexander Mikhalitsyn Cc: Trond Myklebust , Anna Schumaker , Alexander Viro , Christian Brauner , Jan Kara , "Seth Forshee (DigitalOcean)" , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Date: Tue, 03 Feb 2026 11:21:25 -0500 In-Reply-To: References: <20260129-twmount-v1-1-4874ed2a15c4@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Tue, 2026-02-03 at 17:11 +0100, Alexander Mikhalitsyn wrote: > Am Do., 29. Jan. 2026 um 22:48 Uhr schrieb Jeff Layton : > >=20 > > Commit e1c5ae59c0f2 ("fs: don't allow non-init s_user_ns for filesystem= s > > without FS_USERNS_MOUNT") prevents the mount of any filesystem inside a > > container that doesn't have FS_USERNS_MOUNT set. > >=20 >=20 > Hi Jeff, >=20 > > This broke NFS mounts in our containerized environment. We have a daemo= n > > somewhat like systemd-mountfsd running in the init_ns. A process does a > > fsopen() inside the container and passes it to the daemon via unix > > socket. > >=20 > > The daemon then vets that the request is for an allowed NFS server and > > performs the mount. This now fails because the fc->user_ns is set to th= e > > value in the container and NFS doesn't set FS_USERNS_MOUNT. We don't > > want to add FS_USERNS_MOUNT to NFS since that would allow the container > > to mount any NFS server (even malicious ones). > >=20 > > Add a new FS_USERNS_DELEGATABLE flag, and enable it on NFS. >=20 > Great idea, very similar to what we have with BPFFS/BPF Tokens. >=20 > Taking into account this patch, shouldn't we drop FS_USERNS_MOUNT and > replace it with > FS_USERNS_DELEGATABLE for bpffs too? >=20 > I mean something like: >=20 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > $ git diff > diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c > index 9f866a010dad..d8dfdc846bd0 100644 > --- a/kernel/bpf/inode.c > +++ b/kernel/bpf/inode.c > @@ -1009,10 +1009,6 @@ static int bpf_fill_super(struct super_block > *sb, struct fs_context *fc) > struct inode *inode; > int ret; >=20 > - /* Mounting an instance of BPF FS requires privileges */ > - if (fc->user_ns !=3D &init_user_ns && !capable(CAP_SYS_ADMIN)) > - return -EPERM; > - > ret =3D simple_fill_super(sb, BPF_FS_MAGIC, bpf_rfiles); > if (ret) > return ret; > @@ -1085,7 +1081,7 @@ static struct file_system_type bpf_fs_type =3D { > .init_fs_context =3D bpf_init_fs_context, > .parameters =3D bpf_fs_parameters, > .kill_sb =3D bpf_kill_super, > - .fs_flags =3D FS_USERNS_MOUNT, > + .fs_flags =3D FS_USERNS_DELEGATABLE, > }; >=20 > static int __init bpf_init(void) > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >=20 > Because it feels like we were basically implementing this FS_USERNS_DELEG= ATABLE > flag implicitly for BPFFS before. I can submit a patch for BPFFS later > after testing. >=20 Yeah, looks like a good thing to change, since it should have the same effect. Assuming that works the way it should: Reviewed-by: Jeff Layton