linux-kernel - Re: [PATCH bpf-next 2/4] bpf: Implement bpf_local

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Date:   Wed, 27 May 2020 14:38:40 +0200
From:   KP Singh <kpsingh@...omium.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     KP Singh <kpsingh@...omium.org>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, bpf@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        James Morris <jmorris@...ei.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Martin KaFai Lau <kafai@...com>,
        Florent Revest <revest@...omium.org>
Subject: Re: [PATCH bpf-next 2/4] bpf: Implement bpf_local_storage for inodes

On 26-May 22:08, Christoph Hellwig wrote:
> On Tue, May 26, 2020 at 06:33:34PM +0200, KP Singh wrote:
> > From: KP Singh <kpsingh@...gle.com>
> > 
> > Similar to bpf_local_storage for sockets, add local storage for inodes.
> > The life-cycle of storage is managed with the life-cycle of the inode.
> > i.e. the storage is destroyed along with the owning inode.
> > 
> > Since, the intention is to use this in LSM programs, the destruction is
> > done after security_inode_free in __destroy_inode.
> 
> NAK onbloating the inode structure.  Please find an out of line way
> to store your information.

The other alternative is to use lbs_inode (security blobs) and we can
do this without adding fields to struct inode.

Here is a rough diff (only illustrative, won't apply cleanly) of the
changes needed to this patch:

 https://gist.github.com/sinkap/1d213d17fb82a5e8ffdc3f320ec37d79

Once tracing has gets a whitelist based access to inode storage, I
guess it, too, can use bpf_local_storage for inodes if CONFIG_BPF_LSM
is enabled. Does this sound reasonable to the BPF folks?

- KP