releases/4.9.167/tun-properly-test-for-iff_up.patch

   1 From foo@baz Thu Mar 28 21:57:57 CET 2019
   2 From: Eric Dumazet <edumazet@google.com>
   3 Date: Thu, 14 Mar 2019 20:19:47 -0700
   4 Subject: tun: properly test for IFF_UP
   5
   6 From: Eric Dumazet <edumazet@google.com>
   7
   8 [ Upstream commit 4477138fa0ae4e1b699786ef0600863ea6e6c61c ]
   9
  10 Same reasons than the ones explained in commit 4179cb5a4c92
  11 ("vxlan: test dev->flags & IFF_UP before calling netif_rx()")
  12
  13 netif_rx_ni() or napi_gro_frags() must be called under a strict contract.
  14
  15 At device dismantle phase, core networking clears IFF_UP
  16 and flush_all_backlogs() is called after rcu grace period
  17 to make sure no incoming packet might be in a cpu backlog
  18 and still referencing the device.
  19
  20 A similar protocol is used for gro layer.
  21
  22 Most drivers call netif_rx() from their interrupt handler,
  23 and since the interrupts are disabled at device dismantle,
  24 netif_rx() does not have to check dev->flags & IFF_UP
  25
  26 Virtual drivers do not have this guarantee, and must
  27 therefore make the check themselves.
  28
  29 Fixes: 1bd4978a88ac ("tun: honor IFF_UP in tun_get_user()")
  30 Signed-off-by: Eric Dumazet <edumazet@google.com>
  31 Reported-by: syzbot <syzkaller@googlegroups.com>
  32 Signed-off-by: David S. Miller <davem@davemloft.net>
  33 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  34 ---
  35  drivers/net/tun.c |   15 +++++++++++----
  36  1 file changed, 11 insertions(+), 4 deletions(-)
  37
  38 --- a/drivers/net/tun.c
  39 +++ b/drivers/net/tun.c
  40 @@ -1194,9 +1194,6 @@ static ssize_t tun_get_user(struct tun_s
  41         u32 rxhash;
  42         ssize_t n;
  43
  44 -       if (!(tun->dev->flags & IFF_UP))
  45 -               return -EIO;
  46 -
  47         if (!(tun->flags & IFF_NO_PI)) {
  48                 if (len < sizeof(pi))
  49                         return -EINVAL;
  50 @@ -1273,9 +1270,11 @@ static ssize_t tun_get_user(struct tun_s
  51                 err = skb_copy_datagram_from_iter(skb, 0, from, len);
  52
  53         if (err) {
  54 +               err = -EFAULT;
  55 +drop:
  56                 this_cpu_inc(tun->pcpu_stats->rx_dropped);
  57                 kfree_skb(skb);
  58 -               return -EFAULT;
  59 +               return err;
  60         }
  61
  62         err = virtio_net_hdr_to_skb(skb, &gso, tun_is_little_endian(tun));
  63 @@ -1327,7 +1326,15 @@ static ssize_t tun_get_user(struct tun_s
  64         skb_probe_transport_header(skb, 0);
  65
  66         rxhash = skb_get_hash(skb);
  67 +
  68 +       rcu_read_lock();
  69 +       if (unlikely(!(tun->dev->flags & IFF_UP))) {
  70 +               err = -EIO;
  71 +               goto drop;
  72 +       }
  73 +
  74         netif_rx_ni(skb);
  75 +       rcu_read_unlock();
  76
  77         stats = get_cpu_ptr(tun->pcpu_stats);
  78         u64_stats_update_begin(&stats->syncp);