netdev - Re: [PATCH net-next 4/4] selinux: bpf: Add addtional check for bpf object file receive

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Date:   Thu, 05 Oct 2017 01:52:59 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Chenbo Feng <chenbofeng.kernel@...il.com>, netdev@...r.kernel.org,
        SELinux <Selinux@...ho.nsa.gov>,
        linux-security-module@...r.kernel.org
CC:     Jeffrey Vander Stoep <jeffv@...gle.com>,
        Lorenzo Colitti <lorenzo@...gle.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Chenbo Feng <fengc@...gle.com>
Subject: Re: [PATCH net-next 4/4] selinux: bpf: Add addtional check for bpf
 object file receive

On 10/05/2017 01:44 AM, Daniel Borkmann wrote:
> On 10/04/2017 08:29 PM, Chenbo Feng wrote:
>> From: Chenbo Feng <fengc@...gle.com>
>>
>> Introduce a bpf object related check when sending and receiving files
>> through unix domain socket as well as binder. It checks if the receiving
>> process have privilege to read/write the bpf map or use the bpf program.
>> This check is necessary because the bpf maps and programs are using a
>> anonymous inode as their shared inode so the normal way of checking the
>> files and sockets when passing between processes cannot work properly on
>> eBPF object. This check only works when the BPF_SYSCALL is configured.
>
> [...]
>> +/* This function will check the file pass through unix socket or binder to see
>> + * if it is a bpf related object. And apply correspinding checks on the bpf
>> + * object based on the type. The bpf maps and programs, not like other files and
>> + * socket, are using a shared anonymous inode inside the kernel as their inode.
>> + * So checking that inode cannot identify if the process have privilege to
>> + * access the bpf object and that's why we have to add this additional check in
>> + * selinux_file_receive and selinux_binder_transfer_files.
>> + */
> [...]
>
> If selinux/lsm folks have some input on this one in particular, would
> be great. The issue is not really tied to bpf specifically, but to the
> use of anon-inodes wrt fd passing. Maybe some generic resolution can
> be found to tackle this ...

Perhaps even just a generic callback in struct file_operations might be
better in order to just retrieve the secctx from the underlying object
in case of anon-inodes and then have a generic check in selinux_file_receive()
for the case when such callback is set, such that we don't need to put
specific bpf logic there.