linux-kernel - Re: [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs

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Message-ID: <CAOQ4uxg=maKZi=5Xet4mC1=uUXftyyKZagj0TBBm8emPDaLmtg@mail.gmail.com>
Date:   Tue, 28 Aug 2018 21:42:09 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Jonathan Corbet <corbet@....net>,
        Vivek Goyal <vgoyal@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout

On Tue, Aug 28, 2018 at 8:43 PM Amir Goldstein <amir73il@...il.com> wrote:
>
> On Tue, Aug 28, 2018 at 7:53 PM Mark Salyzyn <salyzyn@...roid.com> wrote:
> >
> > Assumption never checked, should fail if the mounter creds are not
> > sufficient.
> >
> > Signed-off-by: Mark Salyzyn <salyzyn@...roid.com>
> > Cc: Miklos Szeredi <miklos@...redi.hu>
> > Cc: Jonathan Corbet <corbet@....net>
> > Cc: Vivek Goyal <vgoyal@...hat.com>
> > Cc: Eric W. Biederman <ebiederm@...ssion.com>
> > Cc: Amir Goldstein <amir73il@...il.com>
> > Cc: Randy Dunlap <rdunlap@...radead.org>
> > Cc: Stephen Smalley <sds@...ho.nsa.gov>
> > Cc: linux-unionfs@...r.kernel.org
> > Cc: linux-doc@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> >
> > v5
> > - dependency of "overlayfs: override_creds=off option bypass creator_cred"
> > ---
> >  fs/overlayfs/overlayfs.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> > index 7538b9b56237..bf3a80157d42 100644
> > --- a/fs/overlayfs/overlayfs.h
> > +++ b/fs/overlayfs/overlayfs.h
> > @@ -176,7 +176,7 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
> >
> >  static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
> >  {
> > -       int err = vfs_whiteout(dir, dentry);
> > +       int err = capable(CAP_MKNOD) ? vfs_whiteout(dir, dentry) : -EPERM;
>
> Should that be ns_capable()? Should the test go into vfs_whiteout()?
> I feel there is no convention at all.
>

Nevermind, I don't think creating a whiteout poses any risk, so don't think
we need to worry about CAP_MKNOD.

Thanks,
Amir.