linux-kernel - Re: [PATCH bpf-next 1/6] bpf: introduce BPF_PROG_TYPE_FILE

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Message-ID: <20181005044659.GU32577@ZenIV.linux.org.uk>
Date:   Fri, 5 Oct 2018 05:46:59 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>, daniel@...earbox.net,
        luto@...capital.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH bpf-next 1/6] bpf: introduce BPF_PROG_TYPE_FILE_FILTER

On Wed, Oct 03, 2018 at 07:57:45PM -0700, Alexei Starovoitov wrote:

> @@ -15,6 +15,7 @@
>  #include <linux/bpf.h>
>  #include <linux/bpf-cgroup.h>
>  #include <net/sock.h>
> +#include <../fs/mount.h>

No.

> +	struct file *file = NULL;
> +	struct inode *inode;
> +	struct super_block *sb;
> +	struct mount *mnt;

Fuck, no.

> +	case offsetof(struct bpf_file_info, mnt_id):
> +		/* dst = real_mount(file->f_path.mnt)->mnt_id */
> +		mnt = real_mount(LD_1(file->f_path.mnt));
> +		LD_n(mnt->mnt_id);

NAK.  Anything in struct mount is private to just a couple of
files in fs/*.c.  Don't do that.  And keep in mind that internal
details can and will be changed at zero notice, so be careful
with adding such stuff.

Another problem is your direct poking in ->i_ino.  It's not
something directly exposed to userland at the moment and it should
not become such.  Filesystem has every right to have ->getattr()
set ->ino (== ->st_ino value) in whichever way it likes; the same
goes for ->dev.