From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: David Ahern <dsahern@gmail.com>, David Ahern <dsahern@kernel.org>,
netdev@vger.kernel.org, davem@davemloft.net, kuba@kernel.org,
daniel@iogearbox.net, john.fastabend@gmail.com, ast@kernel.org,
kafai@fb.com, songliubraving@fb.com, yhs@fb.com, andriin@fb.com,
brouer@redhat.com
Subject: Re: [PATCH RFC bpf-next 0/4] bpf: Add support for XDP programs in DEVMAPs
Date: Mon, 25 May 2020 14:56:26 +0200 [thread overview]
Message-ID: <87pnasi35x.fsf@toke.dk> (raw)
In-Reply-To: <20200525144752.3e87f8cd@carbon>
Jesper Dangaard Brouer <brouer@redhat.com> writes:
> On Mon, 25 May 2020 14:15:32 +0200
> Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
>> David Ahern <dsahern@gmail.com> writes:
>>
>> > On 5/22/20 9:59 AM, Toke Høiland-Jørgensen wrote:
>> >> David Ahern <dsahern@kernel.org> writes:
>> >>
>> >>> Implementation of Daniel's proposal for allowing DEVMAP entries to be
>> >>> a device index, program id pair. Daniel suggested an fd to specify the
>> >>> program, but that seems odd to me that you insert the value as an fd, but
>> >>> read it back as an id since the fd can be closed.
>> >>
>> >> While I can be sympathetic to the argument that it seems odd, every
>> >> other API uses FD for insert and returns ID, so why make it different
>> >> here? Also, the choice has privilege implications, since the CAP_BPF
>> >> series explicitly makes going from ID->FD a more privileged operation
>> >> than just querying the ID.
>
> Sorry, I don't follow.
> Can someone explain why is inserting an ID is a privilege problem?
See description here:
https://lore.kernel.org/bpf/20200513230355.7858-1-alexei.starovoitov@gmail.com/
Specifically, this part:
> Consolidating all CAP checks at load time makes security model similar to
> open() syscall. Once the user got an FD it can do everything with it.
> read/write/poll don't check permissions. The same way when bpf_prog_load
> command returns an FD the user can do everything (including attaching,
> detaching, and bpf_test_run).
>
> The important design decision is to allow ID->FD transition for
> CAP_SYS_ADMIN only. What it means that user processes can run
> with CAP_BPF and CAP_NET_ADMIN and they will not be able to affect each
> other unless they pass FDs via scm_rights or via pinning in bpffs.
>> > I do not like the model where the kernel changes the value the user
>> > pushed down.
>>
>> Yet it's what we do in every other interface where a user needs to
>> supply a program, including in prog array maps. So let's not create a
>> new inconsistent interface here...
>
> I sympathize with Ahern on this. It seems very weird to insert/write
> one value-type, but read another value-type.
Yeah, I do kinda agree that it's a bit weird. But it's what we do
everywhere else, so I think consistency wins out here. There might be an
argument that maps should be different (because they're conceptually a
read/write data structure not a syscall return value). But again, we
already have a map type that takes prog IDs, and that already does the
rewriting, so doing it different here would be even weirder...
-Toke
next prev parent reply other threads:[~2020-05-25 12:56 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-22 1:05 [PATCH RFC bpf-next 0/4] bpf: Add support for XDP programs in DEVMAPs David Ahern
2020-05-22 1:05 ` [PATCH RFC bpf-next 1/4] bpf: Handle 8-byte values in DEVMAP and DEVMAP_HASH David Ahern
2020-05-22 12:08 ` Jesper Dangaard Brouer
2020-05-22 16:04 ` Jesper Dangaard Brouer
2020-05-22 18:11 ` David Ahern
2020-05-22 1:05 ` [PATCH RFC bpf-next 2/4] bpf: Add support to attach bpf program to a devmap David Ahern
2020-05-22 16:02 ` Toke Høiland-Jørgensen
2020-05-22 17:45 ` David Ahern
2020-05-22 1:05 ` [PATCH RFC bpf-next 3/4] xdp: Add xdp_txq_info to xdp_buff David Ahern
2020-05-22 16:04 ` Toke Høiland-Jørgensen
2020-05-22 17:45 ` David Ahern
2020-05-22 1:05 ` [PATCH RFC bpf-next 4/4] bpftool: Add SEC name for xdp programs attached to device map David Ahern
2020-05-22 11:17 ` [PATCH RFC bpf-next 0/4] bpf: Add support for XDP programs in DEVMAPs Jesper Dangaard Brouer
2020-05-22 15:59 ` Toke Høiland-Jørgensen
2020-05-22 17:46 ` David Ahern
2020-05-25 12:15 ` Toke Høiland-Jørgensen
2020-05-25 12:47 ` Jesper Dangaard Brouer
2020-05-25 12:56 ` Toke Høiland-Jørgensen [this message]
2020-05-26 23:36 ` Daniel Borkmann
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