[PATCH net] ip_gre: clear feature flags when incompatible o_flags are set

[Sabrina Dubroca]

Commit dd9d598c6657 ("ip_gre: add the support for i/o_flags update via
netlink") added the ability to change o_flags, but missed that the
GSO/LLTX features are disabled by default, and only enabled some gre
features are unused. Thus we also need to disable the GSO/LLTX features
on the device when the TUNNEL_SEQ or TUNNEL_CSUM flags are set.

These two examples should result in the same features being set:

    ip link add gre_none type gre local 192.168.0.10 remote 192.168.0.20 ttl 
255 key 0

    ip link set gre_none type gre seq
    ip link add gre_seq type gre local 192.168.0.10 remote 192.168.0.20 ttl 255 
key 1 seq

Fixes: dd9d598c6657 ("ip_gre: add the support for i/o_flags update via netlink")
Signed-off-by: Sabrina Dubroca <s...@queasysnail.net>
---
 net/ipv4/ip_gre.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index a8772a978224..9c169bb2444d 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -781,8 +781,14 @@ static void ipgre_link_update(struct net_device *dev, bool 
set_mtu)
                    tunnel->encap.type == TUNNEL_ENCAP_NONE) {
                        dev->features |= NETIF_F_GSO_SOFTWARE;
                        dev->hw_features |= NETIF_F_GSO_SOFTWARE;
+               } else {
+                       dev->features &= ~NETIF_F_GSO_SOFTWARE;
+                       dev->hw_features &= ~NETIF_F_GSO_SOFTWARE;
                }
                dev->features |= NETIF_F_LLTX;
+       } else {
+               dev->hw_features &= ~NETIF_F_GSO_SOFTWARE;
+               dev->features &= ~(NETIF_F_LLTX | NETIF_F_GSO_SOFTWARE);
        }
 }
 
-- 
2.16.2