[ovs-dev] [PATCH 1/2] datapath: backport: OVS: Ignore negative headroom value

[Pravin B Shelar]

Upstream commit:
    commit 5ef9f289c4e698054e5687edb54f0da3cdc9173a
    Author: Ian Wienand <iwienand at redhat.com>
    Date:   Wed Aug 3 15:44:57 2016 +1000

    OVS: Ignore negative headroom value

    net_device->ndo_set_rx_headroom (introduced in
    871b642adebe300be2e50aa5f65a418510f636ec) says

      "Setting a negtaive value reset the rx headroom
       to the default value".

    It seems that the OVS implementation in
    3a927bc7cf9d0fbe8f4a8189dd5f8440228f64e7 overlooked this and sets
    dev->needed_headroom unconditionally.

    This doesn't have an immediate effect, but can mess up later
    LL_RESERVED_SPACE calculations, such as done in
    net/ipv6/mcast.c:mld_newpack.  For reference, this issue was found
    from a skb_panic raised there after the length calculations had given
    the wrong result.

    Note the other current users of this interface
    (drivers/net/tun.c:tun_set_headroom and
    drivers/net/veth.c:veth_set_rx_headroom) are both checking this
    correctly thus need no modification.

    Thanks to Ben for some pointers from the crash dumps!

    Cc: Benjamin Poirier <bpoirier at suse.com>
    Cc: Paolo Abeni <pabeni at redhat.com>
    Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1361414
    Signed-off-by: Ian Wienand <iwienand at redhat.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>

Signed-off-by: Pravin B Shelar <pshelar at ovn.org>
---
 datapath/vport-internal_dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/datapath/vport-internal_dev.c b/datapath/vport-internal_dev.c
index 198bae6..482af37 100644
--- a/datapath/vport-internal_dev.c
+++ b/datapath/vport-internal_dev.c
@@ -141,7 +141,7 @@ internal_get_stats(struct net_device *dev, struct rtnl_link_stats64 *stats)
 #ifdef HAVE_IFF_PHONY_HEADROOM
 static void internal_set_rx_headroom(struct net_device *dev, int new_hr)
 {
-	dev->needed_headroom = new_hr;
+	dev->needed_headroom = new_hr < 0 ? 0 : new_hr;
 }
 #endif
 
-- 
1.9.1