netdev - Re: [PATCH RFC bpf-next 0/4] bpf: Add support for XDP programs in DEVMAPs

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Message-ID: <f94be4c8-c547-1be0-98c8-7e7cd3b7ee71@gmail.com>
Date:   Fri, 22 May 2020 11:46:50 -0600
From:   David Ahern <dsahern@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, brouer@...hat.com,
        daniel@...earbox.net, john.fastabend@...il.com, ast@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com, andriin@...com
Subject: Re: [PATCH RFC bpf-next 0/4] bpf: Add support for XDP programs in
 DEVMAPs

On 5/22/20 9:59 AM, Toke Høiland-Jørgensen wrote:
> David Ahern <dsahern@...nel.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.
> 

I do not like the model where the kernel changes the value the user
pushed down.