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Date:   Mon, 22 Oct 2018 11:15:47 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        steffen.klassert@...unet.com
Subject: Re: [RFC PATCH v2 02/10] udp: implement GRO for plain UDP sockets.

On Mon, Oct 22, 2018 at 6:13 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On Sun, 2018-10-21 at 16:06 -0400, Willem de Bruijn wrote:
> > On Fri, Oct 19, 2018 at 10:30 AM Paolo Abeni <pabeni@...hat.com> wrote:
> > >
> > > This is the RX counterpart of commit bec1f6f69736 ("udp: generate gso
> > > with UDP_SEGMENT"). When UDP_GRO is enabled, such socket is also
> > > eligible for GRO in the rx path: UDP segments directed to such socket
> > > are assembled into a larger GSO_UDP_L4 packet.
> > >
> > > The core UDP GRO support is enabled with setsockopt(UDP_GRO).
> > >
> > > Initial benchmark numbers:
> > >
> > > Before:
> > > udp rx:   1079 MB/s   769065 calls/s
> > >
> > > After:
> > > udp rx:   1466 MB/s    24877 calls/s
> > >
> > >
> > > This change introduces a side effect in respect to UDP tunnels:
> > > after a UDP tunnel creation, now the kernel performs a lookup per ingress
> > > UDP packet, while before such lookup happened only if the ingress packet
> > > carried a valid internal header csum.
> > >
> > > v1 -> v2:
> > >  - use a new option to enable UDP GRO
> > >  - use static keys to protect the UDP GRO socket lookup
> > >
> > > Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> > > ---
> > >  include/linux/udp.h      |   3 +-
> > >  include/uapi/linux/udp.h |   1 +
> > >  net/ipv4/udp.c           |   7 +++
> > >  net/ipv4/udp_offload.c   | 109 +++++++++++++++++++++++++++++++--------
> > >  net/ipv6/udp_offload.c   |   6 +--
> > >  5 files changed, 98 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/include/linux/udp.h b/include/linux/udp.h
> > > index a4dafff407fb..f613b329852e 100644
> > > --- a/include/linux/udp.h
> > > +++ b/include/linux/udp.h
> > > @@ -50,11 +50,12 @@ struct udp_sock {
> > >         __u8             encap_type;    /* Is this an Encapsulation socket? */
> > >         unsigned char    no_check6_tx:1,/* Send zero UDP6 checksums on TX? */
> > >                          no_check6_rx:1,/* Allow zero UDP6 checksums on RX? */
> > > -                        encap_enabled:1; /* This socket enabled encap
> > > +                        encap_enabled:1, /* This socket enabled encap
> > >                                            * processing; UDP tunnels and
> > >                                            * different encapsulation layer set
> > >                                            * this
> > >                                            */
> > > +                        gro_enabled:1; /* Can accept GRO packets */
> > >
> > >         /*
> > >          * Following member retains the information to create a UDP header
> > >          * when the socket is uncorked.
> > > diff --git a/include/uapi/linux/udp.h b/include/uapi/linux/udp.h
> > > index 09502de447f5..30baccb6c9c4 100644
> > > --- a/include/uapi/linux/udp.h
> > > +++ b/include/uapi/linux/udp.h
> > > @@ -33,6 +33,7 @@ struct udphdr {
> > >  #define UDP_NO_CHECK6_TX 101   /* Disable sending checksum for UDP6X */
> > >  #define UDP_NO_CHECK6_RX 102   /* Disable accpeting checksum for UDP6 */
> > >  #define UDP_SEGMENT    103     /* Set GSO segmentation size */
> > > +#define UDP_GRO                104     /* This socket can receive UDP GRO packets */
> > >
> > >  /* UDP encapsulation types */
> > >  #define UDP_ENCAP_ESPINUDP_NON_IKE     1 /* draft-ietf-ipsec-nat-t-ike-00/01 */
> > > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > > index 9fcb5374e166..3c277378814f 100644
> > > --- a/net/ipv4/udp.c
> > > +++ b/net/ipv4/udp.c
> > > @@ -115,6 +115,7 @@
> > >  #include "udp_impl.h"
> > >  #include <net/sock_reuseport.h>
> > >  #include <net/addrconf.h>
> > > +#include <net/udp_tunnel.h>
> > >
> > >  struct udp_table udp_table __read_mostly;
> > >  EXPORT_SYMBOL(udp_table);
> > > @@ -2459,6 +2460,12 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
> > >                 up->gso_size = val;
> > >                 break;
> > >
> > > +       case UDP_GRO:
> > > +               if (valbool)
> > > +                       udp_tunnel_encap_enable(sk->sk_socket);
> > > +               up->gro_enabled = valbool;
> >
> > The socket lock is not held here, so multiple updates to
> > up->gro_enabled and the up->encap_enabled and the static branch can
> > race. Syzkaller is adept at generating those.
>
> Good catch. I was fooled by the current existing code. I think there
> are potentially similar issues for UDP_ENCAP, UDPLITE_SEND_CSCOV, ...
>
> Since the rx path don't take it anymore and we don't risk starving, I
> think we should could/always acquire the socket lock on setsockopt,
> wdyt?

Agreed. We had to add a lot of those in packet_setsockopt for the same reason.

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