Commit 6f0f3657 authored Mar 14, 2019 by Eric Dumazet Committed by Greg Kroah-Hartman Apr 03, 2019

tun: properly test for IFF_UP



[ Upstream commit 4477138fa0ae4e1b699786ef0600863ea6e6c61c ]

Same reasons than the ones explained in commit 4179cb5a4c92
("vxlan: test dev->flags & IFF_UP before calling netif_rx()")

netif_rx_ni() or napi_gro_frags() must be called under a strict contract.

At device dismantle phase, core networking clears IFF_UP
and flush_all_backlogs() is called after rcu grace period
to make sure no incoming packet might be in a cpu backlog
and still referencing the device.

A similar protocol is used for gro layer.

Most drivers call netif_rx() from their interrupt handler,
and since the interrupts are disabled at device dismantle,
netif_rx() does not have to check dev->flags & IFF_UP

Virtual drivers do not have this guarantee, and must
therefore make the check themselves.

Fixes: 1bd4978a ("tun: honor IFF_UP in tun_get_user()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent b731b5d0

drivers/net/tun.c

+11 −4

Original line number	Diff line number	Diff line
		@@ -1194,9 +1194,6 @@ static ssize_t tun_get_user(struct tun_struct tun, struct tun_file tfile,
		u32 rxhash;
		ssize_t n;

		if (!(tun->dev->flags & IFF_UP))
		return -EIO;

		if (!(tun->flags & IFF_NO_PI)) {
		if (len < sizeof(pi))
		return -EINVAL;
		@@ -1273,9 +1270,11 @@ static ssize_t tun_get_user(struct tun_struct tun, struct tun_file tfile,
		err = skb_copy_datagram_from_iter(skb, 0, from, len);

		if (err) {
		err = -EFAULT;
		drop:
		this_cpu_inc(tun->pcpu_stats->rx_dropped);
		kfree_skb(skb);
		return -EFAULT;
		return err;
		}

		err = virtio_net_hdr_to_skb(skb, &gso, tun_is_little_endian(tun));
		@@ -1327,7 +1326,15 @@ static ssize_t tun_get_user(struct tun_struct tun, struct tun_file tfile,
		skb_probe_transport_header(skb, 0);

		rxhash = skb_get_hash(skb);

		rcu_read_lock();
		if (unlikely(!(tun->dev->flags & IFF_UP))) {
		err = -EIO;
		goto drop;
		}

		netif_rx_ni(skb);
		rcu_read_unlock();

		stats = get_cpu_ptr(tun->pcpu_stats);
		u64_stats_update_begin(&stats->syncp);