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Date: Tue, 20 Aug 2019 17:29:11 +0200 From: Björn Töpel <bjorn.topel@...il.com> To: Daniel Borkmann <daniel@...earbox.net> Cc: syzbot+c82697e3043781e08802@...kaller.appspotmail.com, Alexei Starovoitov <ast@...nel.org>, Netdev <netdev@...r.kernel.org>, Björn Töpel <bjorn.topel@...el.com>, bpf <bpf@...r.kernel.org>, David Miller <davem@...emloft.net>, Jesper Dangaard Brouer <hawk@...nel.org>, Jakub Kicinski <jakub.kicinski@...ronome.com>, John Fastabend <john.fastabend@...il.com>, Jonathan Lemon <jonathan.lemon@...il.com>, Martin KaFai Lau <kafai@...com>, LKML <linux-kernel@...r.kernel.org>, "Karlsson, Magnus" <magnus.karlsson@...el.com>, Song Liu <songliubraving@...com>, syzkaller-bugs@...glegroups.com, Xdp <xdp-newbies@...r.kernel.org>, Yonghong Song <yhs@...com>, hdanton@...a.com Subject: Re: [PATCH bpf-next] xsk: proper socket state check in xsk_poll On Tue, 20 Aug 2019 at 16:30, Daniel Borkmann <daniel@...earbox.net> wrote: > > On 8/20/19 12:04 PM, Björn Töpel wrote: > > From: Björn Töpel <bjorn.topel@...el.com> > > > > The poll() implementation for AF_XDP sockets did not perform the > > proper state checks, prior accessing the socket umem. This patch fixes > > that by performing a xsk_is_bound() check. > > > > Suggested-by: Hillf Danton <hdanton@...a.com> > > Reported-by: syzbot+c82697e3043781e08802@...kaller.appspotmail.com > > Fixes: 77cd0d7b3f25 ("xsk: add support for need_wakeup flag in AF_XDP rings") > > Signed-off-by: Björn Töpel <bjorn.topel@...el.com> > > --- > > net/xdp/xsk.c | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c > > index ee4428a892fa..08bed5e92af4 100644 > > --- a/net/xdp/xsk.c > > +++ b/net/xdp/xsk.c > > @@ -356,13 +356,20 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m, > > return err; > > } > > > > +static bool xsk_is_bound(struct xdp_sock *xs) > > +{ > > + struct net_device *dev = READ_ONCE(xs->dev); > > + > > + return dev && xs->state == XSK_BOUND; > > +} > > + > > 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(!xs->dev)) > > + if (unlikely(!xsk_is_bound(xs))) > > return -ENXIO; > > if (unlikely(!(xs->dev->flags & IFF_UP))) > > return -ENETDOWN; > > @@ -383,6 +390,9 @@ static unsigned int xsk_poll(struct file *file, struct socket *sock, > > struct net_device *dev = xs->dev; > > struct xdp_umem *umem = xs->umem; > > > > + if (unlikely(!xsk_is_bound(xs))) > > + return mask; > > + > > if (umem->need_wakeup) > > dev->netdev_ops->ndo_xsk_wakeup(dev, xs->queue_id, > > umem->need_wakeup); > > @@ -417,7 +427,7 @@ static void xsk_unbind_dev(struct xdp_sock *xs) > > { > > struct net_device *dev = xs->dev; > > > > - if (!dev || xs->state != XSK_BOUND) > > + if (!xsk_is_bound(xs)) > > return; > > I think I'm a bit confused by your READ_ONCE() usage. ;-/ I can see why you're > using it in xsk_is_bound() above, but then at the same time all the other callbacks > like xsk_poll() or xsk_unbind_dev() above have a struct net_device *dev = xs->dev > right before the test. Could you elaborate? > Yes, now I'm confused as well! Digging deeper... I believe there are a couple of places in xsk.c that do not have READ_ONCE/WRITE_ONCE-correctness. Various xdp_sock members are read lock-less outside the control plane mutex (mutex member of struct xdp_sock). This needs some re-work. I'll look into using the newly introduced state member (with corresponding read/write barriers) for this. I'll cook some patch(es) that address this, but first it sounds like I need to reread [1] two, or three times. At least. ;-) Thanks, Björn [1] https://lwn.net/Articles/793253/ > Thanks, > Daniel
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