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: 1bd4978a88ac ("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>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 24cc94453d38c4021688ba510aeef9cd4f605050..c32df13a863082cbc144ba8faff71a7906eaa5c5 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -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);