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Message-ID: <20210124221854.GA1487@fieldses.org>
Date: Sun, 24 Jan 2021 17:18:54 -0500
From: "J. Bruce Fields" <bfields@...ldses.org>
To: Christian Brauner <christian.brauner@...ntu.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Christoph Hellwig <hch@....de>, linux-fsdevel@...r.kernel.org,
John Johansen <john.johansen@...onical.com>,
James Morris <jmorris@...ei.org>,
Mimi Zohar <zohar@...ux.ibm.com>,
Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
Stephen Smalley <stephen.smalley.work@...il.com>,
Casey Schaufler <casey@...aufler-ca.com>,
Arnd Bergmann <arnd@...db.de>,
Andreas Dilger <adilger.kernel@...ger.ca>,
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
Geoffrey Thomas <geofft@...reload.com>,
Mrunal Patel <mpatel@...hat.com>,
Josh Triplett <josh@...htriplett.org>,
Andy Lutomirski <luto@...nel.org>,
Theodore Tso <tytso@....edu>, Alban Crequy <alban@...volk.io>,
Tycho Andersen <tycho@...ho.ws>,
David Howells <dhowells@...hat.com>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Seth Forshee <seth.forshee@...onical.com>,
Stéphane Graber <stgraber@...ntu.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Aleksa Sarai <cyphar@...har.com>,
Lennart Poettering <lennart@...ttering.net>,
"Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org,
Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>,
Kees Cook <keescook@...omium.org>,
Todd Kjos <tkjos@...gle.com>, Paul Moore <paul@...l-moore.com>,
Jonathan Corbet <corbet@....net>,
containers@...ts.linux-foundation.org,
linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
linux-integrity@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH v6 05/39] namei: make permission helpers idmapped mount
aware
On Sat, Jan 23, 2021 at 02:09:58PM +0100, Christian Brauner wrote:
> On Fri, Jan 22, 2021 at 05:26:32PM -0500, J. Bruce Fields wrote:
> > If I NFS-exported an idmapped mount, I think I'd expect idmapped clients
> > to see the mapped IDs.
> >
> > Looks like that means taking the user namespace from the struct
> > svc_export everwhere, for example:
> >
> > On Thu, Jan 21, 2021 at 02:19:24PM +0100, Christian Brauner wrote:
> > > index 66f2ef67792a..8d90796e236a 100644
> > > --- a/fs/nfsd/nfsfh.c
> > > +++ b/fs/nfsd/nfsfh.c
> > > @@ -40,7 +40,8 @@ static int nfsd_acceptable(void *expv, struct dentry *dentry)
> > > /* make sure parents give x permission to user */
> > > int err;
> > > parent = dget_parent(tdentry);
> > > - err = inode_permission(d_inode(parent), MAY_EXEC);
> > > + err = inode_permission(&init_user_ns,
> > > + d_inode(parent), MAY_EXEC);
> >
> > err = inode_permission(exp->ex_path.mnt->mnt_userns,
> > d_inode(parent, MAY_EXEC);
>
> Hey Bruce, thanks! Imho, the clean approach for now is to not export
> idmapped mounts until we have ported that part of nfs similar to what we
> do for stacking filesystems for now. I've tested and taken this patch
> into my tree:
Oh good, thanks. My real fear was that we'd fix this up later and leave
users in a situation where the server exposes different IDs depending on
kernel version, which would be a mess. Looks like this should avoid
that.
As for making idmapped mounts actually work with nfsd--are you planning
to do that, or do you need me to? I hope the patch is straightforward;
I'm more worried testing it.
--b.
>
> ---
> >From 7a6a53bca1ecd8db872de1ee81d1a57e1829e525 Mon Sep 17 00:00:00 2001
> From: Christian Brauner <christian.brauner@...ntu.com>
> Date: Sat, 23 Jan 2021 12:00:02 +0100
> Subject: [PATCH] nfs: do not export idmapped mounts
>
> Prevent nfs from exporting idmapped mounts until we have ported it to
> support exporting idmapped mounts.
>
> Cc: Christoph Hellwig <hch@....de>
> Cc: David Howells <dhowells@...hat.com>
> Cc: "J. Bruce Fields" <bfields@...hat.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: linux-fsdevel@...r.kernel.org
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> ---
> /* v2 */
>
> /* v3 */
>
> /* v4 */
>
> /* v5 */
>
> /* v5 */
> patch introduced
> base-commit: 19c329f6808995b142b3966301f217c831e7cf31
> ---
> fs/nfsd/export.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> index 81e7bb12aca6..e456421f68b4 100644
> --- a/fs/nfsd/export.c
> +++ b/fs/nfsd/export.c
> @@ -369,8 +369,9 @@ static struct svc_export *svc_export_update(struct svc_export *new,
> struct svc_export *old);
> static struct svc_export *svc_export_lookup(struct svc_export *);
>
> -static int check_export(struct inode *inode, int *flags, unsigned char *uuid)
> +static int check_export(struct path *path, int *flags, unsigned char *uuid)
> {
> + struct inode *inode = d_inode(path->dentry);
>
> /*
> * We currently export only dirs, regular files, and (for v4
> @@ -394,6 +395,7 @@ static int check_export(struct inode *inode, int *flags, unsigned char *uuid)
> * or an FSID number (so NFSEXP_FSID or ->uuid is needed).
> * 2: We must be able to find an inode from a filehandle.
> * This means that s_export_op must be set.
> + * 3: We must not currently be on an idmapped mount.
> */
> if (!(inode->i_sb->s_type->fs_flags & FS_REQUIRES_DEV) &&
> !(*flags & NFSEXP_FSID) &&
> @@ -408,6 +410,11 @@ static int check_export(struct inode *inode, int *flags, unsigned char *uuid)
> return -EINVAL;
> }
>
> + if (mnt_user_ns(path->mnt) != &init_user_ns) {
> + dprintk("exp_export: export of idmapped mounts not yet supported.\n");
> + return -EINVAL;
> + }
> +
> if (inode->i_sb->s_export_op->flags & EXPORT_OP_NOSUBTREECHK &&
> !(*flags & NFSEXP_NOSUBTREECHECK)) {
> dprintk("%s: %s does not support subtree checking!\n",
> @@ -636,8 +643,7 @@ static int svc_export_parse(struct cache_detail *cd, char *mesg, int mlen)
> goto out4;
> }
>
> - err = check_export(d_inode(exp.ex_path.dentry), &exp.ex_flags,
> - exp.ex_uuid);
> + err = check_export(&exp.ex_path, &exp.ex_flags, exp.ex_uuid);
> if (err)
> goto out4;
> /*
> --
> 2.30.0
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