On Tue, Sep 09, 2025 at 08:33:27AM -0700, Eric Dumazet wrote:
On Tue, Sep 9, 2025 at 8:19 AM Richard W.M. Jones <rjones@xxxxxxxxxx> wrote:
On Tue, Sep 09, 2025 at 07:47:09AM -0700, Eric Dumazet wrote:
> On Tue, Sep 9, 2025 at 7:37 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
> >
> > On 9/9/25 8:35 AM, Eric Dumazet wrote:
> > > On Tue, Sep 9, 2025 at 7:04 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> > >>
> > >> On Tue, Sep 9, 2025 at 6:32 AM Richard W.M. Jones <rjones@xxxxxxxxxx> wrote:
> > >>>
> > >>> On Tue, Sep 09, 2025 at 01:22:43PM +0000, Eric Dumazet wrote:
> > >>>> Recently, syzbot started to abuse NBD with all kinds of sockets.
> > >>>>
> > >>>> Commit cf1b2326b734 ("nbd: verify socket is supported during setup")
> > >>>> made sure the socket supported a shutdown() method.
> > >>>>
> > >>>> Explicitely accept TCP and UNIX stream sockets.
> > >>>
> > >>> I'm not clear what the actual problem is, but I will say that libnbd &
> > >>> nbdkit (which are another NBD client & server, interoperable with the
> > >>> kernel) we support and use NBD over vsock[1]. And we could support
> > >>> NBD over pretty much any stream socket (Infiniband?) [2].
> > >>>
> > >>> [1] https://libguestfs.org/nbd_aio_connect_vsock.3.html
> > >>> https://libguestfs.org/nbdkit-service.1.html#AF_VSOCK
> > >>> [2] https://libguestfs.org/nbd_connect_socket.3.html
> > >>>
> > >>> TCP and Unix domain sockets are by far the most widely used, but I
> > >>> don't think it's fair to exclude other socket types.
> > >>
> > >> If we have known and supported socket types, please send a patch to add them.
> > >>
> > >> I asked the question last week and got nothing about vsock or other types.
> > >>
> > >> https://lore.kernel.org/netdev/CANn89iLNFHBMTF2Pb6hHERYpuih9eQZb6A12+ndzBcQs_kZoBA@xxxxxxxxxxxxxx/
> > >>
> > >> For sure, we do not want datagram sockets, RAW, netlink, and many others.
> > >
> > > BTW vsock will probably fire lockdep warnings, I see GFP_KERNEL
> > > being used in net/vmw_vsock/virtio_transport.c
CC-ing Stefan & Stefano. Myself, I'm only using libnbd
(ie. userspace) over vsock, not the kernel client.
Thanks Rich for cceing me!
> > > So you will have to fix this.
How we should fix that?
IIUC GFP_KERNEL in virtio_transport.c is used only by workqueue's
functions, but we have GFP_ATOMIC in the fast path that can be called
when the user is sending a packet.
This is basically the driver for the virtio-vsock device that can
allocates extra buffers to be exposed to the device.
In this case the allocation can happen in virtqueue_add_sgs() for virtio
indirect buffer, that IIRC virtio-vsock is not using currently (but we
don't know in the future).
In any case, we use GFP_KERNEL also in virtio_transport_common.c to
allocate the sk_buff, so that should be the same issue.
Thanks,
Stefano
