Breno Leitao wrote:
> On Wed, Apr 12, 2023 at 10:28:41AM -0400, Willem de Bruijn wrote:
> > Breno Leitao wrote:
> > > On Tue, Apr 11, 2023 at 09:28:29AM -0600, Jens Axboe wrote:
> > > > On 4/11/23 9:24?AM, Willem de Bruijn wrote:
> > > > > Jens Axboe wrote:
> > > > >> On 4/11/23 9:00?AM, Willem de Bruijn wrote:
> > > > >> But that doesn't work, because sock->ops->ioctl() assumes the arg is
> > > > >> memory in userspace. Or do you mean change all of the sock->ops->ioctl()
> > > > >> to pass in on-stack memory (or similar) and have it work with a kernel
> > > > >> address?
> > > > >
> > > > > That was what I suggested indeed.
> > > > >
> > > > > It's about as much code change as this patch series. But it avoids
> > > > > the code duplication.
> > > >
> > > > Breno, want to tackle that as a prep patch first? Should make the
> > > > functional changes afterwards much more straightforward, and will allow
> > > > support for anything really.
> > >
> > > Absolutely. I just want to make sure that I got the proper approach that
> > > we agreed here.
> > >
> > > Let me explain what I understood taking TCP as an example:
> > >
> > > 1) Rename tcp_ioctl() to something as _tcp_ioctl() where the 'arg'
> > > argument is now just a kernel memory (located in the stack frame from the
> > > callee).
> > >
> > > 2) Recreate "tcp_ioctl()" that will basically allocate a 'arg' in the
> > > stack and call _tcp_ioctl() passing that 'arg' argument. At the bottom of
> > > this (tcp_ioctl() function) function, call `put_user(in_kernel_arg, userspace_arg)
> > >
> > > 3) Repeat it for the 20 protocols that implement ioctl:
> > >
> > > ag "struct proto .* = {" -A 20 net/ | grep \.ioctl
> > > net/dccp/ipv6.c .ioctl = dccp_ioctl,
> > > net/dccp/ipv4.c .ioctl = dccp_ioctl,
> > > net/ieee802154/socket.c .ioctl = dgram_ioctl,
> > > net/ipv4/udplite.c .ioctl = udp_ioctl,
> > > net/ipv4/raw.c .ioctl = raw_ioctl,
> > > net/ipv4/udp.c .ioctl = udp_ioctl,
> > > net/ipv4/tcp_ipv4.c .ioctl = tcp_ioctl,
> > > net/ipv6/raw.c .ioctl = rawv6_ioctl,
> > > net/ipv6/tcp_ipv6.c .ioctl = tcp_ioctl,
> > > net/ipv6/udp.c .ioctl = udp_ioctl,
> > > net/ipv6/udplite.c .ioctl = udp_ioctl,
> > > net/l2tp/l2tp_ip6.c .ioctl = l2tp_ioctl,
> > > net/l2tp/l2tp_ip.c .ioctl = l2tp_ioctl,
> > > net/phonet/datagram.: .ioctl = pn_ioctl,
> > > net/phonet/pep.c .ioctl = pep_ioctl,
> > > net/rds/af_rds.c .ioctl = rds_ioctl,
> > > net/sctp/socket.c .ioctl = sctp_ioctl,
> > > net/sctp/socket.c .ioctl = sctp_ioctl,
> > > net/xdp/xsk.c .ioctl = sock_no_ioctl,
> > > net/mptcp/protocol.c .ioctl = mptcp_ioctl,
> > >
> > > Am I missing something?
> >
> > The suggestion is to convert all to take kernel memory and do the
> > put_cmsg in the caller of .ioctl. Rather than create a wrapper for
> > each individual instance and add a separate .iouring_cmd for each.
> >
> > "change all of the sock->ops->ioctl() to pass in on-stack memory
> > (or similar) and have it work with a kernel address"
>
> is it possible to do it for cases where we don't know what is the size
> of the buffer?
>
> For instance the raw_ioctl()/rawv6_ioctl() case. The "arg" argument is
> used in different ways (one for input and one for output):
>
> 1) If cmd == SIOCOUTQ or SIOCINQ, then the return value will be
> returned to userspace:
> put_user(amount, (int __user *)arg)
>
> 2) For default cmd, ipmr_ioctl() is called, which reads from the `arg`
> parameter:
> copy_from_user(&vr, arg, sizeof(vr)
>
> How to handle these contradictory behaviour ahead of time (at callee
> time, where the buffers will be prepared)?
>
> Thank you!
Ah you found a counter-example to the simple pattern of put_user.
The answer perhaps depends on how many such counter-examples you
encounter in the list you gave. If this is the only one, exceptions
in the wrapper are reasonable. Not if there are many.
Is the intent for io_uring to support all cases eventually? The
current patch series only targeted more common fast path operations.
Probably also relevant is whether/how the approach can be extended
to [gs]etsockopt, as that was another example given, with the same
challenge.
