linux-kernel - Re: [PATCH v2 03/10] ovl: check privs before decoding file handle

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAOQ4uxhti+COYB3GhfMcPFwpfBRYQvr98oCO9wwS029W5e0A5g@mail.gmail.com>
Date:   Tue, 8 Dec 2020 15:49:25 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     "Eric W . Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 03/10] ovl: check privs before decoding file handle

On Mon, Dec 7, 2020 at 6:36 PM Miklos Szeredi <mszeredi@...hat.com> wrote:
>
> CAP_DAC_READ_SEARCH is required by open_by_handle_at(2) so check it in
> ovl_decode_real_fh() as well to prevent privilege escalation for
> unprivileged overlay mounts.
>
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> ---
>  fs/overlayfs/namei.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index a6162c4076db..82a55fdb1e7a 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -156,6 +156,9 @@ struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
>         struct dentry *real;
>         int bytes;
>
> +       if (!capable(CAP_DAC_READ_SEARCH))
> +               return NULL;
> +

If the mounter is not capable in init ns, ovl_check_origin() and
ovl_verify_index()
will not function as expected and this will break index and nfs export features.
So I think we need to also check capability in ovl_can_decode_fh(), to auto
disable those features.

Thanks,
Amir.