openvswitch.h: Align uAPI definition with the kernel.

Upstream commit:
    commit 1926407a4ab0e59d5a27bed7b82029b356d80fa0
    Author: Ilya Maximets <i.maximets@ovn.org>
    Date:   Wed Mar 9 23:20:33 2022 +0100

    net: openvswitch: fix uAPI incompatibility with existing user space

    Few years ago OVS user space made a strange choice in the commit [1]
    to define types only valid for the user space inside the copy of a
    kernel uAPI header.  '#ifndef __KERNEL__' and another attribute was
    added later.

    This leads to the inevitable clash between user space and kernel types
    when the kernel uAPI is extended.  The issue was unveiled with the
    addition of a new type for IPv6 extension header in kernel uAPI.

    When kernel provides the OVS_KEY_ATTR_IPV6_EXTHDRS attribute to the
    older user space application, application tries to parse it as
    OVS_KEY_ATTR_PACKET_TYPE and discards the whole netlink message as
    malformed.  Since OVS_KEY_ATTR_IPV6_EXTHDRS is supplied along with
    every IPv6 packet that goes to the user space, IPv6 support is fully
    broken.

    Fixing that by bringing these user space attributes to the kernel
    uAPI to avoid the clash.  Strictly speaking this is not the problem
    of the kernel uAPI, but changing it is the only way to avoid breakage
    of the older user space applications at this point.

    These 2 types are explicitly rejected now since they should not be
    passed to the kernel.  Additionally, OVS_KEY_ATTR_TUNNEL_INFO moved
    out from the '#ifdef __KERNEL__' as there is no good reason to hide
    it from the userspace.  And it's also explicitly rejected now, because
    it's for in-kernel use only.

    Comments with warnings were added to avoid the problem coming back.

    (1 << type) converted to (1ULL << type) to avoid integer overflow on
    OVS_KEY_ATTR_IPV6_EXTHDRS, since it equals 32 now.

     [1] beb75a40fdc2 ("userspace: Switching of L3 packets in L2 pipeline")

    Fixes: 28a3f0601727 ("net: openvswitch: IPv6: Add IPv6 extension header support")
    Link: https://lore.kernel.org/netdev/3adf00c7-fe65-3ef4-b6d7-6d8a0cad8a5f@nvidia.com
    Link: https://github.com/openvswitch/ovs/commit/beb75a40fdc295bfd6521b0068b4cd12f6de507c
    Reported-by: Roi Dayan <roid@nvidia.com>
    Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
    Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
    Acked-by: Aaron Conole <aconole@redhat.com>
    Link: https://lore.kernel.org/r/20220309222033.3018976-1-i.maximets@ovn.org
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Not adding OVS_KEY_ATTR_IPV6_EXTHDRS in this commit as this is not
necessary.  Will be added along with the actual userspace
implementation.

This change should help avoiding incompatibility issues in the future.

Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

2 files changed, 19 insertions, 10 deletions

diff --git a/datapath/flow_netlink.c b/datapath/flow_netlink.c
index 996041602..caed44386 100644
--- a/datapath/flow_netlink.c
+++ b/datapath/flow_netlink.c
@@ -359,7 +359,7 @@ size_t ovs_key_attr_size(void)
 	/* Whenever adding new OVS_KEY_ FIELDS, we should consider
 	 * updating this function.
 	 */
-	BUILD_BUG_ON(OVS_KEY_ATTR_TUNNEL_INFO != 29);
+	BUILD_BUG_ON(OVS_KEY_ATTR_MAX != 31);
 
 	return    nla_total_size(4)   /* OVS_KEY_ATTR_PRIORITY */
 		+ nla_total_size(0)   /* OVS_KEY_ATTR_TUNNEL */
@@ -491,6 +491,13 @@ static int __parse_flow_nlattrs(const struct nlattr *attr,
 			return -EINVAL;
 		}
 
+		if (type == OVS_KEY_ATTR_PACKET_TYPE ||
+		    type == OVS_KEY_ATTR_ND_EXTENSIONS ||
+		    type == OVS_KEY_ATTR_TUNNEL_INFO) {
+			OVS_NLERR(log, "Key type %d is not supported", type);
+			return -EINVAL;
+		}
+
 		if (attrs & (1ULL << type)) {
 			OVS_NLERR(log, "Duplicate key (type %d).", type);
 			return -EINVAL;
diff --git a/datapath/linux/compat/include/linux/openvswitch.h b/datapath/linux/compat/include/linux/openvswitch.h
index 8d9300091..8bb5abdc8 100644
--- a/datapath/linux/compat/include/linux/openvswitch.h
+++ b/datapath/linux/compat/include/linux/openvswitch.h
@@ -388,17 +388,19 @@ enum ovs_key_attr {
 	OVS_KEY_ATTR_CT_ORIG_TUPLE_IPV6,   /* struct ovs_key_ct_tuple_ipv6 */
 	OVS_KEY_ATTR_NSH,       /* Nested set of ovs_nsh_key_* */
 
-#ifdef __KERNEL__
-	/* Only used within kernel data path. */
-	OVS_KEY_ATTR_TUNNEL_INFO,  /* struct ovs_tunnel_info */
-#endif
-
-#ifndef __KERNEL__
-	/* Only used within userspace data path. */
-	OVS_KEY_ATTR_PACKET_TYPE,  /* be32 packet type */
+	/* User space decided to squat on types 29 and 30.  They are defined
+	 * below, but should not be sent to the kernel.
+	 *
+	 * WARNING: No new types should be added unless they are defined
+	 *          for both kernel and user space (no 'ifdef's).  It's hard
+	 *          to keep compatibility otherwise.
+	 */
+	OVS_KEY_ATTR_PACKET_TYPE,   /* be32 packet type */
 	OVS_KEY_ATTR_ND_EXTENSIONS, /* struct ovs_key_nd_extensions */
-#endif
 
+	OVS_KEY_ATTR_TUNNEL_INFO,   /* struct ip_tunnel_info.
+				     * For in-kernel use only.
+				     */
 	__OVS_KEY_ATTR_MAX
 };