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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 25 May 2020 14:47:52 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     David Ahern <dsahern@...il.com>, David Ahern <dsahern@...nel.org>,
        netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        daniel@...earbox.net, john.fastabend@...il.com, ast@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com, andriin@...com,
        brouer@...hat.com
Subject: Re: [PATCH RFC bpf-next 0/4] bpf: Add support for XDP programs in
 DEVMAPs

On Mon, 25 May 2020 14:15:32 +0200
Toke Høiland-Jørgensen <toke@...hat.com> wrote:

> David Ahern <dsahern@...il.com> writes:
> 
> > 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.

Sorry, I don't follow.
Can someone explain why is inserting an ID is a privilege problem?

   
> >
> > 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.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer