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    Subject[PATCH 5.0 026/146] tun: properly test for IFF_UP
    Date
    5.0-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
    @@ -1763,9 +1763,6 @@ static ssize_t tun_get_user(struct tun_s
    int skb_xdp = 1;
    bool frags = tun_napi_frags_enabled(tfile);

    - if (!(tun->dev->flags & IFF_UP))
    - return -EIO;
    -
    if (!(tun->flags & IFF_NO_PI)) {
    if (len < sizeof(pi))
    return -EINVAL;
    @@ -1867,6 +1864,8 @@ 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);
    if (frags) {
    @@ -1874,7 +1873,7 @@ static ssize_t tun_get_user(struct tun_s
    mutex_unlock(&tfile->napi_mutex);
    }

    - return -EFAULT;
    + return err;
    }
    }

    @@ -1958,6 +1957,12 @@ static ssize_t tun_get_user(struct tun_s
    !tfile->detached)
    rxhash = __skb_get_hash_symmetric(skb);

    + rcu_read_lock();
    + if (unlikely(!(tun->dev->flags & IFF_UP))) {
    + err = -EIO;
    + goto drop;
    + }
    +
    if (frags) {
    /* Exercise flow dissector code path. */
    u32 headlen = eth_get_headlen(skb->data, skb_headlen(skb));
    @@ -1965,6 +1970,7 @@ static ssize_t tun_get_user(struct tun_s
    if (unlikely(headlen > skb_headlen(skb))) {
    this_cpu_inc(tun->pcpu_stats->rx_dropped);
    napi_free_frags(&tfile->napi);
    + rcu_read_unlock();
    mutex_unlock(&tfile->napi_mutex);
    WARN_ON(1);
    return -ENOMEM;
    @@ -1992,6 +1998,7 @@ static ssize_t tun_get_user(struct tun_s
    } else {
    netif_rx_ni(skb);
    }
    + rcu_read_unlock();

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

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