Subject: Re: [PATCH bpf-next 1/6] bpf: introduce BPF_PROG_TYPE_FILE_FILTER

From: Al Viro <[email-masked]>
Date: Fri, 5 Oct 2018 05:46:59 +0100

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.