On Mon, Sep 30, 2019 at 03:30:12PM +0200, Magnus Karlsson wrote:
> Fixes a crash in poll() when an AF_XDP socket is opened in copy mode
> with the XDP_USE_NEED_WAKEUP flag set and the bound device does not
> have ndo_xsk_wakeup defined. Avoid trying to call the non-existing ndo
> and instead call the internal xsk sendmsg functionality to send
> packets in the same way (from the application's point of view) as
> calling sendmsg() in any mode or poll() in zero-copy mode would have
> done. The application should behave in the same way independent on if
> zero-copy mode or copy-mode is used.
>
> Fixes: 77cd0d7b3f25 ("xsk: add support for need_wakeup flag in AF_XDP rings")
> Reported-by: syzbot+a5765ed8cdb1cca4d249@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
Overall looks good, two very small nits:
> ---
> net/xdp/xsk.c | 33 +++++++++++++++++++++++----------
> 1 file changed, 23 insertions(+), 10 deletions(-)
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index c2f1af3..a478d8ec 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -327,8 +327,7 @@ static void xsk_destruct_skb(struct sk_buff *skb)
> sock_wfree(skb);
> }
>
> -static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
> - size_t total_len)
> +static int xsk_generic_xmit(struct sock *sk)
> {
> u32 max_batch = TX_BATCH_SIZE;
> struct xdp_sock *xs = xdp_sk(sk);
> @@ -394,22 +393,31 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
> return err;
> }
>
> -static int xsk_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
> +static int __xsk_sendmsg(struct socket *sock)
> {
> - bool need_wait = !(m->msg_flags & MSG_DONTWAIT);
> struct sock *sk = sock->sk;
> struct xdp_sock *xs = xdp_sk(sk);
Can't we just only pass xs as an argument to __xsk_sendmsg()? From
below xsk_sendmsg() we eventually fetch xs anyway same as for the
xsk_poll(), yet in __xsk_sendmsg() we pass sock (which is otherwise
unused) and then we need to refetch sk and xs once again.
> - if (unlikely(!xsk_is_bound(xs)))
> - return -ENXIO;
> if (unlikely(!(xs->dev->flags & IFF_UP)))
> return -ENETDOWN;
> if (unlikely(!xs->tx))
> return -ENOBUFS;
> +
> + return xs->zc ? xsk_zc_xmit(sk) : xsk_generic_xmit(sk);
> +}
> +
> +static int xsk_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
> +{
> + bool need_wait = !(m->msg_flags & MSG_DONTWAIT);
> + struct sock *sk = sock->sk;
> + struct xdp_sock *xs = xdp_sk(sk);
> +
> + if (unlikely(!xsk_is_bound(xs)))
> + return -ENXIO;
> if (need_wait)
Not directly related but since you touch this code, need_wait should
be marked unlikely() as well.
> return -EOPNOTSUPP;
>
> - return (xs->zc) ? xsk_zc_xmit(sk) : xsk_generic_xmit(sk, m, total_len);
> + return __xsk_sendmsg(sock);
> }
>
> static unsigned int xsk_poll(struct file *file, struct socket *sock,
> @@ -426,9 +434,14 @@ static unsigned int xsk_poll(struct file *file, struct socket *sock,
> dev = xs->dev;
> umem = xs->umem;
>
> - if (umem->need_wakeup)
> - dev->netdev_ops->ndo_xsk_wakeup(dev, xs->queue_id,
> - umem->need_wakeup);
> + if (umem->need_wakeup) {
> + if (dev->netdev_ops->ndo_xsk_wakeup)
> + dev->netdev_ops->ndo_xsk_wakeup(dev, xs->queue_id,
> + umem->need_wakeup);
> + else
> + /* Poll needs to drive Tx also in copy mode */
> + __xsk_sendmsg(sock);
> + }
>
> if (xs->rx && !xskq_empty_desc(xs->rx))
> mask |= POLLIN | POLLRDNORM;
> --
> 2.7.4
>
