On 8/26/19 8:10 AM, Björn Töpel wrote:
From: Björn Töpel <bjorn.topel@xxxxxxxxx>
The state variable was read, and written outside the control mutex
(struct xdp_sock, mutex), without proper barriers and {READ,
WRITE}_ONCE correctness.
In this commit this issue is addressed, and the state member is now
used a point of synchronization whether the socket is setup correctly
or not.
This also fixes a race, found by syzcaller, in xsk_poll() where umem
could be accessed when stale.
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>
Sorry for the delay.
---
net/xdp/xsk.c | 57 ++++++++++++++++++++++++++++++++++++---------------
1 file changed, 40 insertions(+), 17 deletions(-)
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index f3351013c2a5..8fafa3ce3ae6 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -162,10 +162,23 @@ static int __xsk_rcv_zc(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
return err;
}
+static bool xsk_is_bound(struct xdp_sock *xs)
+{
+ if (READ_ONCE(xs->state) == XSK_BOUND) {
+ /* Matches smp_wmb() in bind(). */
+ smp_rmb();
+ return true;
+ }
+ return false;
+}
+
int xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
{
u32 len;
+ if (!xsk_is_bound(xs))
+ return -EINVAL;
+
if (xs->dev != xdp->rxq->dev || xs->queue_id != xdp->rxq->queue_index)
return -EINVAL;
@@ -362,7 +375,7 @@ static int xsk_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
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;
@@ -378,10 +391,15 @@ static unsigned int xsk_poll(struct file *file, struct socket *sock,
struct poll_table_struct *wait)
{
unsigned int mask = datagram_poll(file, sock, wait);
- struct sock *sk = sock->sk;
- struct xdp_sock *xs = xdp_sk(sk);
- struct net_device *dev = xs->dev;
- struct xdp_umem *umem = xs->umem;
+ struct xdp_sock *xs = xdp_sk(sock->sk);
+ struct net_device *dev;
+ struct xdp_umem *umem;
+
+ if (unlikely(!xsk_is_bound(xs)))
+ return mask;
+
+ dev = xs->dev;
+ umem = xs->umem;
if (umem->need_wakeup)
dev->netdev_ops->ndo_xsk_wakeup(dev, xs->queue_id,
@@ -417,10 +435,9 @@ static void xsk_unbind_dev(struct xdp_sock *xs)
{
struct net_device *dev = xs->dev;
- if (!dev || xs->state != XSK_BOUND)
+ if (xs->state != XSK_BOUND)
return;
-
- xs->state = XSK_UNBOUND;
+ WRITE_ONCE(xs->state, XSK_UNBOUND);
/* Wait for driver to stop using the xdp socket. */
xdp_del_sk_umem(xs->umem, xs);
@@ -495,7 +512,9 @@ static int xsk_release(struct socket *sock)
local_bh_enable();
xsk_delete_from_maps(xs);
+ mutex_lock(&xs->mutex);
xsk_unbind_dev(xs);
+ mutex_unlock(&xs->mutex);
xskq_destroy(xs->rx);
xskq_destroy(xs->tx);
@@ -589,19 +608,18 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
}
umem_xs = xdp_sk(sock->sk);
- if (!umem_xs->umem) {
- /* No umem to inherit. */
+ if (!xsk_is_bound(umem_xs)) {
err = -EBADF;
sockfd_put(sock);
goto out_unlock;
- } else if (umem_xs->dev != dev || umem_xs->queue_id != qid) {
+ }
+ if (umem_xs->dev != dev || umem_xs->queue_id != qid) {
err = -EINVAL;
sockfd_put(sock);
goto out_unlock;
}
-
xdp_get_umem(umem_xs->umem);
- xs->umem = umem_xs->umem;
+ WRITE_ONCE(xs->umem, umem_xs->umem);
sockfd_put(sock);
} else if (!xs->umem || !xdp_umem_validate_queues(xs->umem)) {
err = -EINVAL;
@@ -626,10 +644,15 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
xdp_add_sk_umem(xs->umem, xs);
out_unlock:
- if (err)
+ if (err) {
dev_put(dev);
- else
- xs->state = XSK_BOUND;
+ } else {
+ /* Matches smp_rmb() in bind() for shared umem
+ * sockets, and xsk_is_bound().
+ */
+ smp_wmb();
You write with what this barrier matches/pairs, but would be useful for readers
to have an explanation against what it protects. I presume to have things like
xs->umem public as you seem to guard it behind xsk_is_bound() in xsk_poll() and
other cases? Would be great to have a detailed analysis of all this e.g. in the
commit message so one wouldn't need to guess; right now it feels this is doing
many things at once and w/o further explanation of why READ_ONCE() or others are
omitted sometimes. Would be great to get a lot more clarity into this, perhaps
splitting it up a bit might also help.
+ WRITE_ONCE(xs->state, XSK_BOUND);
+ }
Thanks,
Daniel
