From: Xuanqiang Luo ipgre_netlink_parms() can enable collect_md on an existing GRE, GRETAP or ERSPAN device. Unlike newlink, changelink does not enforce metadata tunnel uniqueness. Converting a non-metadata device can therefore replace the metadata receive entry for another device of the same type in the same netns. Deleting either device then clears the shared entry, breaking metadata receive lookup for the surviving device. If parameter validation fails after collect_md is set, deleting the modified device can also clear an entry it never owned. Reject enabling metadata mode in both changelink callbacks before any encapsulation or tunnel parameters are modified. Allow requests that repeat the metadata attribute on an existing metadata device. Fixes: 2e15ea390e6f ("ip_gre: Add support to collect tunnel metadata.") Signed-off-by: Xuanqiang Luo --- The state change on failure can be reproduced without an existing metadata tunnel (output abbreviated): # ip link add g1 type gre local 192.0.2.1 remote 192.0.2.2 # ip -d link show g1 link/gre 192.0.2.1 peer 192.0.2.2 ... gre remote 192.0.2.2 local 192.0.2.1 ... # ip link set g1 type gre external RTNETLINK answers: Invalid argument # ip -d link show g1 link/none c0:00:02:01 peer c0:00:02:02 ... gre external remote 192.0.2.2 local 192.0.2.1 ... # ip link del g1 The request fails, but collect_md and the device type have already changed. If another metadata tunnel exists, deleting this device can clear its collect_md_tun entry. A successful conversion can overwrite that entry. 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 82309efd417e0..7b1b0f17f60b9 100644 --- a/net/ipv4/ip_gre.c +++ b/net/ipv4/ip_gre.c @@ -1464,6 +1464,9 @@ static int ipgre_changelink(struct net_device *dev, struct nlattr *tb[], if (!rtnl_dev_link_net_capable(dev, t->net)) return -EPERM; + if (data && data[IFLA_GRE_COLLECT_METADATA] && !t->collect_md) + return -EOPNOTSUPP; + err = ipgre_newlink_encap_setup(dev, data); if (err) return err; @@ -1496,6 +1499,9 @@ static int erspan_changelink(struct net_device *dev, struct nlattr *tb[], if (!rtnl_dev_link_net_capable(dev, t->net)) return -EPERM; + if (data && data[IFLA_GRE_COLLECT_METADATA] && !t->collect_md) + return -EOPNOTSUPP; + err = ipgre_newlink_encap_setup(dev, data); if (err) return err; base-commit: c9151088f1674fd29ff26a20f5fc687acf53a2f0 -- 2.43.0