[PATCH bpf-next] xsk: proper socket state check in xsk_poll

[BjÃrn TÃpel]

From: BjÃrn TÃpel <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: BjÃrn TÃpel <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;
 
 	xs->state = XSK_UNBOUND;
-- 
2.20.1