Re: [PATCH net-next v11 07/23] ovpn: introduce the ovpn_socket object

[Sergey Ryazanov]

On 15.11.2024 16:28, Antonio Quartulli wrote:
> On 10/11/2024 19:26, Sergey Ryazanov wrote:
> > On 29.10.2024 12:47, Antonio Quartulli wrote:

[...]

> > > +static bool ovpn_socket_hold(struct ovpn_socket *sock)
> > > +{
> > > +    return kref_get_unless_zero(&sock->refcount);
> >
> > Why do we need to wrap this kref acquiring call into the function. Why 
> > we cannot simply call kref_get_unless_zero() from ovpn_socket_get()?
>
> Generally I prefer to keep the API among objects consistent.
> In this specific case, it means having hold() and put() helpers in order 
> to avoid calling kref_* functions directly in the code.
>
> This is a pretty simple case because hold() is called only once, but I 
> still like to be consistent.

Make sense. The counterpart ovpn_socket_hold() function declared in the 
header file. Probably that's why I missed it. Shall we move the holding 
routine there as well?

[...]

> > > +int ovpn_udp_socket_attach(struct socket *sock, struct ovpn_struct 
> > > *ovpn)
> > > +{
> > > +    struct ovpn_socket *old_data;
> > > +    int ret = 0;
> > > +
> > > +    /* sanity check */
> > > +    if (sock->sk->sk_protocol != IPPROTO_UDP) {
> >
> > The function will be called only for a UDP socket. The caller makes 
> > sure this is truth. So, why do we need this check?
>
> To avoid this function being copied/called somewhere else in the future 
> and we forget about this critical assumption.

Shall we do the same for all other functions in this file? E.g. 
ovpn_udp_socket_detach/ovpn_udp_send_skb? And who is giving guarantee 
that the code will be copied together with the check?

> Indeed it's a just sanity check.

Shall we check for pointers validity before dereferencing them?

if (!ovpn || !sock || !sock->sk || !sock->sk->sk_protocol != IPPROTO_UDP) {

With the above questions I would like to show that it's endless number 
of possible mistakes. And no matter how much do we check, a creative 
engineer will find a way to ruin the kernel.

So, is it worth to spend code lines for checking socket for being UDP 
inside a function that has '_udp_' in its name and is called only inside 
the module?

> > > +        DEBUG_NET_WARN_ON_ONCE(1);
> > > +        return -EINVAL;
> > > +    }

--
Sergey