Messages in this thread | | | Subject | Re: [PATCH bpf-next] xsk: proper socket state check in xsk_poll | From | Daniel Borkmann <> | Date | Tue, 20 Aug 2019 23:24:19 +0200 |
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On 8/20/19 5:29 PM, Björn Töpel wrote: > On Tue, 20 Aug 2019 at 16:30, Daniel Borkmann <daniel@iogearbox.net> wrote: >> On 8/20/19 12:04 PM, Björn Töpel wrote: >>> From: Björn Töpel <bjorn.topel@intel.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@sina.com> >>> Reported-by: syzbot+c82697e3043781e08802@syzkaller.appspotmail.com >>> Fixes: 77cd0d7b3f25 ("xsk: add support for need_wakeup flag in AF_XDP rings") >>> Signed-off-by: Björn Töpel <bjorn.topel@intel.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
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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