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References: <20200409212859.GH28467@miu.piliscsaba.redhat.com>
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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Tue, 5 May 2020 12:50:56 +0200
Message-ID: <CAJfpegs3QbWa3gDGNv1atmanP_SE1KE3RhehQ7A+n_cNOa3Bsg@mail.gmail.com>
Subject: Re: [PATCH] vfs: allow unprivileged whiteout creation
To:     Ondrej Mosnacek <omosnace@redhat.com>
Cc:     Al Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org,
        Linux Security Module list 
        <linux-security-module@vger.kernel.org>
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On Fri, May 1, 2020 at 4:46 PM Ondrej Mosnacek <omosnace@redhat.com> wrote:
>
> On Fri, May 1, 2020 at 9:31 AM Miklos Szeredi <miklos@szeredi.hu> wrote:

> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -3505,12 +3505,14 @@ EXPORT_SYMBOL(user_path_create);
> >
> >  int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
> >  {
> > +       bool is_whiteout = S_ISCHR(mode) && dev == WHITEOUT_DEV;
> >         int error = may_create(dir, dentry);
> >
> >         if (error)
> >                 return error;
> >
> > -       if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
> > +       if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD) &&
> > +           !is_whiteout)
>
> Sorry for sidetracking, but !capable(CAP_MKNOD) needs to be last in
> the chain, otherwise you could get a bogus audit report of CAP_MKNOD
> being denied in case is_whiteout is true.

Thanks, fixed in the latest revision.

Miklos