1 files changed, 24 insertions, 10 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index d45ac37e1287..23e9eb66197f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1423,6 +1423,13 @@ static void tun_net_init(struct net_device *dev)
 	dev->max_mtu = MAX_MTU - dev->hard_header_len;
 }
 
+static bool tun_sock_writeable(struct tun_struct *tun, struct tun_file *tfile)
+{
+	struct sock *sk = tfile->socket.sk;
+
+	return (tun->dev->flags & IFF_UP) && sock_writeable(sk);
+}
+
 /* Character device part */
 
 /* Poll */
@@ -1445,10 +1452,14 @@ static __poll_t tun_chr_poll(struct file *file, poll_table *wait)
 	if (!ptr_ring_empty(&tfile->tx_ring))
 		mask |= EPOLLIN | EPOLLRDNORM;
 
-	if (tun->dev->flags & IFF_UP &&
-	    (sock_writeable(sk) ||
-	     (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
-	      sock_writeable(sk))))
+	/* Make sure SOCKWQ_ASYNC_NOSPACE is set if not writable to
+	 * guarantee EPOLLOUT to be raised by either here or
+	 * tun_sock_write_space(). Then process could get notification
+	 * after it writes to a down device and meets -EIO.
+	 */
+	if (tun_sock_writeable(tun, tfile) ||
+	    (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
+	     tun_sock_writeable(tun, tfile)))
 		mask |= EPOLLOUT | EPOLLWRNORM;
 
 	if (tun->dev->reg_state != NETREG_REGISTERED)
@@ -1639,7 +1650,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	else
 		*skb_xdp = 0;
 
-	preempt_disable();
+	local_bh_disable();
 	rcu_read_lock();
 	xdp_prog = rcu_dereference(tun->xdp_prog);
 	if (xdp_prog && !*skb_xdp) {
@@ -1664,7 +1675,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 			if (err)
 				goto err_redirect;
 			rcu_read_unlock();
-			preempt_enable();
+			local_bh_enable();
 			return NULL;
 		case XDP_TX:
 			get_page(alloc_frag->page);
@@ -1673,7 +1684,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 				goto err_redirect;
 			tun_xdp_flush(tun->dev);
 			rcu_read_unlock();
-			preempt_enable();
+			local_bh_enable();
 			return NULL;
 		case XDP_PASS:
 			delta = orig_data - xdp.data;
@@ -1692,7 +1703,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	skb = build_skb(buf, buflen);
 	if (!skb) {
 		rcu_read_unlock();
-		preempt_enable();
+		local_bh_enable();
 		return ERR_PTR(-ENOMEM);
 	}
 
@@ -1702,7 +1713,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	alloc_frag->offset += buflen;
 
 	rcu_read_unlock();
-	preempt_enable();
+	local_bh_enable();
 
 	return skb;
 
@@ -1710,7 +1721,7 @@ err_redirect:
 	put_page(alloc_frag->page);
 err_xdp:
 	rcu_read_unlock();
-	preempt_enable();
+	local_bh_enable();
 	this_cpu_inc(tun->pcpu_stats->rx_dropped);
 	return NULL;
 }
@@ -1906,16 +1917,19 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 		struct bpf_prog *xdp_prog;
 		int ret;
 
+		local_bh_disable();
 		rcu_read_lock();
 		xdp_prog = rcu_dereference(tun->xdp_prog);
 		if (xdp_prog) {
 			ret = do_xdp_generic(xdp_prog, skb);
 			if (ret != XDP_PASS) {
 				rcu_read_unlock();
+				local_bh_enable();
 				return total_len;
 			}
 		}
 		rcu_read_unlock();
+		local_bh_enable();
 	}
 
 	rcu_read_lock();