xdp: fix potential deadlock on socket mutex

There are 2 call chains:

  a) xsk_bind --> xdp_umem_assign_dev
  b) unregister_netdevice_queue --> xsk_notifier

with the following locking order:

  a) xs->mutex --> rtnl_lock
  b) rtnl_lock --> xdp.lock --> xs->mutex

Different order of taking 'xs->mutex' and 'rtnl_lock' could produce a
deadlock here. Fix that by moving the 'rtnl_lock' before 'xs->lock' in
the bind call chain (a).

Reported-by: syzbot+bf64ec93de836d7f4c2c@syzkaller.appspotmail.com
Fixes: 455302d1c9ae ("xdp: fix hang while unregistering device bound to xdp socket")
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index b994c32a664a..59b57d708697 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -430,6 +430,7 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
 	if (flags & ~(XDP_SHARED_UMEM | XDP_COPY | XDP_ZEROCOPY))
 		return -EINVAL;
 
+	rtnl_lock();
 	mutex_lock(&xs->mutex);
 	if (xs->state != XSK_READY) {
 		err = -EBUSY;
@@ -515,6 +516,7 @@ out_unlock:
 		xs->state = XSK_BOUND;
 out_release:
 	mutex_unlock(&xs->mutex);
+	rtnl_unlock();
 	return err;
 }