Re: [PATCH net-next] scm: fix MSG_CTRUNC setting condition for SO_PASSSEC

[Aleksandr Mikhalitsyn]

On Mon, Feb 27, 2023 at 11:01 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Sun, Feb 26, 2023 at 9:17 PM Alexander Mikhalitsyn
> <aleksandr.mikhalitsyn@xxxxxxxxxxxxx> wrote:
> >
> > Currently, we set MSG_CTRUNC flag is we have no
> > msg_control buffer provided and SO_PASSCRED is set
> > or if we have pending SCM_RIGHTS.
> >
> > For some reason we have no corresponding check for
> > SO_PASSSEC.
>

Hi Eric,

> Can you describe what side effects this patch has ?
>
> I think it could break some applications, who might not be able to
> recover from MSG_CTRUNC in this case.
> This should be documented, in order to avoid a future revert.

Yes, it can break applications but only those who use SO_PASSSEC
and not properly check MSG_CTRUNC. According to the recv(2) man:

       MSG_CTRUNC
              indicates that some control data was discarded due to lack
              of space in the buffer for ancillary data.

So, there is no specification about a particular SCM type. It seems more correct
to handle SCM_SECURITY the same way as SCM_RIGHTS / SCM_CREDENTIALS.

>
> In any case, net-next is currently closed.

Oh, I'm sorry.

Kind regards,
Alex