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    Subject[PATCH 4.9 15/56] tun: properly test for IFF_UP
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eric Dumazet <edumazet@google.com>

    [ 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>
    ---
    drivers/net/tun.c | 15 +++++++++++----
    1 file changed, 11 insertions(+), 4 deletions(-)

    --- a/drivers/net/tun.c
    +++ b/drivers/net/tun.c
    @@ -1194,9 +1194,6 @@ static ssize_t tun_get_user(struct tun_s
    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_s
    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_s
    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);

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