On 8/20/19 5:29 PM, Björn Töpel wrote:
On Tue, 20 Aug 2019 at 16:30, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:On 8/20/19 12:04 PM, Björn Töpel wrote:From: Björn Töpel <bjorn.topel@xxxxxxxxx> 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@xxxxxxxx> Reported-by: syzbot+c82697e3043781e08802@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: 77cd0d7b3f25 ("xsk: add support for need_wakeup flag in AF_XDP rings") Signed-off-by: Björn Töpel <bjorn.topel@xxxxxxxxx> --- 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
Right, so even in above two cases, the compiler could have refetched, e.g. dev variable could have first been NULL, but xsk_is_bound() later returns true.
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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