netdev - Re: [RFC v2 08/10] landlock: Handle file system comparisons

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Message-ID: <CALCETrWzfgNvOHmKy5205A2qLJLYCZ+5RZOQR9vzQ1ubpo0vNA@mail.gmail.com>
Date:   Thu, 25 Aug 2016 04:12:02 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Mickaël Salaün <mic@...ikod.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Mack <daniel@...que.org>,
        David Drysdale <drysdale@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        James Morris <james.l.morris@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Paul Moore <pmoore@...hat.com>,
        Sargun Dhillon <sargun@...gun.me>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Will Drewry <wad@...omium.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [RFC v2 08/10] landlock: Handle file system comparisons

On Thu, Aug 25, 2016 at 3:32 AM, Mickaël Salaün <mic@...ikod.net> wrote:
> Add eBPF functions to compare file system access with a Landlock file
> system handle:
> * bpf_landlock_cmp_fs_prop_with_struct_file(prop, map, map_op, file)
>   This function allows to compare the dentry, inode, device or mount
>   point of the currently accessed file, with a reference handle.
> * bpf_landlock_cmp_fs_beneath_with_struct_file(opt, map, map_op, file)
>   This function allows an eBPF program to check if the current accessed
>   file is the same or in the hierarchy of a reference handle.
>
> The goal of file system handle is to abstract kernel objects such as a
> struct file or a struct inode. Userland can create this kind of handle
> thanks to the BPF_MAP_UPDATE_ELEM command. The element is a struct
> landlock_handle containing the handle type (e.g.
> BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) and a file descriptor. This could
> also be any descriptions able to match a struct file or a struct inode
> (e.g. path or glob string).

This needs Eric's opinion.

Also, where do all the struct file *'s get stashed?  Are they
preserved in the arraymap?  What prevents reference cycles or absurdly
large numbers of struct files getting pinned?

--Andy