Re: [PATCH v5 net-next 1/6] net: bridge: add locked entry fdb flag to extend locked port feature

netdev
2022-08-28T11:22:35Z

On 2022-08-27 13:30, Nikolay Aleksandrov wrote:
> On 26/08/2022 14:45, Hans Schultz wrote:
>> Add an intermediate state for clients behind a locked port to allow
>> for
>> possible opening of the port for said clients. The clients mac address
>> will be added with the locked flag set, denying access through the
>> port
>> for the mac address, but also creating a new FDB add event giving
>> userspace daemons the ability to unlock the mac address. This feature
>> corresponds to the Mac-Auth and MAC Authentication Bypass (MAB) named
>> features. The latter defined by Cisco.
>>
>> As locked FDB entries are a security measure to deny access for
>> unauthorized hosts on specific ports, they will deny forwarding from
>> any port to the (MAC, vlan) pair involved and locked entries will not
>> be able by learning or otherwise to change the associated port.
>>
>> Only the kernel can set this FDB entry flag, while userspace can read
>> the flag and remove it by replacing or deleting the FDB entry.
>>
>> Locked entries will age out with the set bridge ageing time.
>>
>> Also add a 'blackhole' fdb flag, ensuring that no forwarding from any
>> port to a destination MAC that has a FDB entry with this flag on will
>> occur. The packets will thus be dropped.
>>
>> Signed-off-by: Hans Schultz <netdev@kapio-technology.com>
>> ---
>> include/linux/if_bridge.h | 1 +
>> include/uapi/linux/if_link.h | 1 +
>> include/uapi/linux/neighbour.h | 4 +++-
>> net/bridge/br_fdb.c | 29 +++++++++++++++++++++++++++++
>> net/bridge/br_input.c | 16 +++++++++++++++-
>> net/bridge/br_netlink.c | 9 ++++++++-
>> net/bridge/br_private.h | 4 +++-
>> 7 files changed, 60 insertions(+), 4 deletions(-)
>>
>
> Hi,
> Please add the blackhole flag in a separate patch.
> A few more comments and questions below..
>

Okay, shall do. :-)

>> diff --git a/include/linux/if_bridge.h b/include/linux/if_bridge.h
>> index d62ef428e3aa..1668ac4d7adc 100644
>> --- a/include/linux/if_bridge.h
>> +++ b/include/linux/if_bridge.h
>> @@ -59,6 +59,7 @@ struct br_ip_list {
>> #define BR_MRP_LOST_IN_CONT BIT(19)
>> #define BR_TX_FWD_OFFLOAD BIT(20)
>> #define BR_PORT_LOCKED BIT(21)
>> +#define BR_PORT_MAB BIT(22)
>>
>> #define BR_DEFAULT_AGEING_TIME (300 * HZ)
>>
>> diff --git a/include/uapi/linux/if_link.h
>> b/include/uapi/linux/if_link.h
>> index e36d9d2c65a7..fcbd0b85ad53 100644
>> --- a/include/uapi/linux/if_link.h
>> +++ b/include/uapi/linux/if_link.h
>> @@ -560,6 +560,7 @@ enum {
>> IFLA_BRPORT_MCAST_EHT_HOSTS_LIMIT,
>> IFLA_BRPORT_MCAST_EHT_HOSTS_CNT,
>> IFLA_BRPORT_LOCKED,
>> + IFLA_BRPORT_MAB,
>> __IFLA_BRPORT_MAX
>> };
>> #define IFLA_BRPORT_MAX (__IFLA_BRPORT_MAX - 1)
>> diff --git a/include/uapi/linux/neighbour.h
>> b/include/uapi/linux/neighbour.h
>> index a998bf761635..bc1440a56b70 100644
>> --- a/include/uapi/linux/neighbour.h
>> +++ b/include/uapi/linux/neighbour.h
>> @@ -52,7 +52,9 @@ enum {
>> #define NTF_STICKY (1 << 6)
>> #define NTF_ROUTER (1 << 7)
>> /* Extended flags under NDA_FLAGS_EXT: */
>> -#define NTF_EXT_MANAGED (1 << 0)
>> +#define NTF_EXT_MANAGED (1 << 0)
>> +#define NTF_EXT_LOCKED (1 << 1)
>> +#define NTF_EXT_BLACKHOLE (1 << 2)
>>
>> /*
>> * Neighbor Cache Entry States.
>> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
>> index e7f4fccb6adb..1962d9594a48 100644
>> --- a/net/bridge/br_fdb.c
>> +++ b/net/bridge/br_fdb.c
>> @@ -105,6 +105,7 @@ static int fdb_fill_info(struct sk_buff *skb,
>> const struct net_bridge *br,
>> struct nda_cacheinfo ci;
>> struct nlmsghdr *nlh;
>> struct ndmsg *ndm;
>> + u32 ext_flags = 0;
>>
>> nlh = nlmsg_put(skb, portid, seq, type, sizeof(*ndm), flags);
>> if (nlh == NULL)
>> @@ -125,11 +126,18 @@ static int fdb_fill_info(struct sk_buff *skb,
>> const struct net_bridge *br,
>> ndm->ndm_flags |= NTF_EXT_LEARNED;
>> if (test_bit(BR_FDB_STICKY, &fdb->flags))
>> ndm->ndm_flags |= NTF_STICKY;
>> + if (test_bit(BR_FDB_ENTRY_LOCKED, &fdb->flags))
>> + ext_flags |= NTF_EXT_LOCKED;
>> + if (test_bit(BR_FDB_BLACKHOLE, &fdb->flags))
>> + ext_flags |= NTF_EXT_BLACKHOLE;
>>
>> if (nla_put(skb, NDA_LLADDR, ETH_ALEN, &fdb->key.addr))
>> goto nla_put_failure;
>> if (nla_put_u32(skb, NDA_MASTER, br->dev->ifindex))
>> goto nla_put_failure;
>> + if (nla_put_u32(skb, NDA_FLAGS_EXT, ext_flags))
>> + goto nla_put_failure;
>> +
>> ci.ndm_used = jiffies_to_clock_t(now - fdb->used);
>> ci.ndm_confirmed = 0;
>> ci.ndm_updated = jiffies_to_clock_t(now - fdb->updated);
>> @@ -171,6 +179,7 @@ static inline size_t fdb_nlmsg_size(void)
>> return NLMSG_ALIGN(sizeof(struct ndmsg))
>> + nla_total_size(ETH_ALEN) /* NDA_LLADDR */
>> + nla_total_size(sizeof(u32)) /* NDA_MASTER */
>> + + nla_total_size(sizeof(u32)) /* NDA_FLAGS_EXT */
>> + nla_total_size(sizeof(u16)) /* NDA_VLAN */
>> + nla_total_size(sizeof(struct nda_cacheinfo))
>> + nla_total_size(0) /* NDA_FDB_EXT_ATTRS */
>> @@ -879,6 +888,10 @@ void br_fdb_update(struct net_bridge *br, struct
>> net_bridge_port *source,
>> &fdb->flags)))
>> clear_bit(BR_FDB_ADDED_BY_EXT_LEARN,
>> &fdb->flags);
>> + if (source->flags & BR_PORT_MAB)
>> + set_bit(BR_FDB_ENTRY_LOCKED, &fdb->flags);
>> + else
>> + clear_bit(BR_FDB_ENTRY_LOCKED, &fdb->flags);
> Please add a test for that bit and only then change it.
>

Okay.

>> }
>>
>> if (unlikely(test_bit(BR_FDB_ADDED_BY_USER, &flags)))
>> @@ -1082,6 +1095,16 @@ static int fdb_add_entry(struct net_bridge *br,
>> struct net_bridge_port *source,
>> modified = true;
>> }
>>
>> + if (test_bit(BR_FDB_ENTRY_LOCKED, &fdb->flags)) {
>> + clear_bit(BR_FDB_ENTRY_LOCKED, &fdb->flags);
>> + modified = true;
>> + }
>> +
>> + if (test_bit(BR_FDB_BLACKHOLE, &fdb->flags)) {
>> + clear_bit(BR_FDB_BLACKHOLE, &fdb->flags);
>> + modified = true;
>> + }
>> +
>> if (fdb_handle_notify(fdb, notify))
>> modified = true;
>>
>> @@ -1178,6 +1201,12 @@ int br_fdb_add(struct ndmsg *ndm, struct nlattr
>> *tb[],
>> vg = nbp_vlan_group(p);
>> }
>>
>> + if (tb[NDA_FLAGS_EXT] &&
>> + (nla_get_u32(tb[NDA_FLAGS_EXT]) & (NTF_EXT_LOCKED |
>> NTF_EXT_BLACKHOLE))) {
>> + pr_info("bridge: RTM_NEWNEIGH has invalid extended flags\n");
>> + return -EINVAL;
>> + }
>> +
>> if (tb[NDA_FDB_EXT_ATTRS]) {
>> attr = tb[NDA_FDB_EXT_ATTRS];
>> err = nla_parse_nested(nfea_tb, NFEA_MAX, attr,
>> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
>> index 68b3e850bcb9..3d48aa7fa778 100644
>> --- a/net/bridge/br_input.c
>> +++ b/net/bridge/br_input.c
>> @@ -110,8 +110,19 @@ int br_handle_frame_finish(struct net *net,
>> struct sock *sk, struct sk_buff *skb
>> br_fdb_find_rcu(br, eth_hdr(skb)->h_source, vid);
>>
>> if (!fdb_src || READ_ONCE(fdb_src->dst) != p ||
>> - test_bit(BR_FDB_LOCAL, &fdb_src->flags))
>> + test_bit(BR_FDB_LOCAL, &fdb_src->flags) ||
>> + test_bit(BR_FDB_ENTRY_LOCKED, &fdb_src->flags)) {
>> + if (!fdb_src || (READ_ONCE(fdb_src->dst) != p &&
>> + (p->flags & BR_LEARNING))) {
>
> please break the second part of the check on a new line instead
>
>> + unsigned long flags = 0;
>> +
>> + if (p->flags & BR_PORT_MAB) {
>
> combine this and the above as one "if" block, no need to have a new one
> here
> which preferrably starts with the MAB check
>

As the above if is an "or", and the MAB check works as an "and", it will
have to be replicated for all "or" checks, thus twice in the above if.
The first check in the above "or" is for new entries, while the second
part of the "or" is to allow roaming to a locked port.

>> + __set_bit(BR_FDB_ENTRY_LOCKED, &flags);
>> + br_fdb_update(br, p, eth_hdr(skb)->h_source, vid, flags);>
>> + }
>> + }
>> goto drop;
>> + }
>> }
>>
>> nbp_switchdev_frame_mark(p, skb);
>> @@ -185,6 +196,9 @@ int br_handle_frame_finish(struct net *net, struct
>> sock *sk, struct sk_buff *skb
>> if (test_bit(BR_FDB_LOCAL, &dst->flags))
>> return br_pass_frame_up(skb);
>>
>> + if (test_bit(BR_FDB_BLACKHOLE, &dst->flags))
>> + goto drop;
>> +
> Not happy about adding a new test in arguably the most used fast-path,
> but I don't see
> a better way to do blackhole right now. Could you please make it an
> unlikely() ?

Surely.

>
> I guess the blackhole flag will be allowed for user-space to set at
> some point, why
> not do it from the start?

I guess it should be so. :-)

>
> Actually adding a BR_FDB_LOCAL and BR_FDB_BLACKHOLE would be a conflict
> above -
> the packet will be received. So you should move the blackhole check
> above the
> BR_FDB_LOCAL one if user-space is allowed to set it to any entry.
>
>> if (now != dst->used)
>> dst->used = now;
>> br_forward(dst->dst, skb, local_rcv, false);
>> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
>> index 5aeb3646e74c..34483420c9e4 100644
>> --- a/net/bridge/br_netlink.c
>> +++ b/net/bridge/br_netlink.c
>> @@ -188,6 +188,7 @@ static inline size_t br_port_info_size(void)
>> + nla_total_size(1) /* IFLA_BRPORT_NEIGH_SUPPRESS */
>> + nla_total_size(1) /* IFLA_BRPORT_ISOLATED */
>> + nla_total_size(1) /* IFLA_BRPORT_LOCKED */
>> + + nla_total_size(1) /* IFLA_BRPORT_MAB */
>> + nla_total_size(sizeof(struct ifla_bridge_id)) /*
>> IFLA_BRPORT_ROOT_ID */
>> + nla_total_size(sizeof(struct ifla_bridge_id)) /*
>> IFLA_BRPORT_BRIDGE_ID */
>> + nla_total_size(sizeof(u16)) /* IFLA_BRPORT_DESIGNATED_PORT */
>> @@ -274,7 +275,8 @@ static int br_port_fill_attrs(struct sk_buff *skb,
>> nla_put_u8(skb, IFLA_BRPORT_MRP_IN_OPEN,
>> !!(p->flags & BR_MRP_LOST_IN_CONT)) ||
>> nla_put_u8(skb, IFLA_BRPORT_ISOLATED, !!(p->flags &
>> BR_ISOLATED)) ||
>> - nla_put_u8(skb, IFLA_BRPORT_LOCKED, !!(p->flags &
>> BR_PORT_LOCKED)))
>> + nla_put_u8(skb, IFLA_BRPORT_LOCKED, !!(p->flags &
>> BR_PORT_LOCKED)) ||
>> + nla_put_u8(skb, IFLA_BRPORT_MAB, !!(p->flags & BR_PORT_MAB)))
>> return -EMSGSIZE;
>>
>> timerval = br_timer_value(&p->message_age_timer);
>> @@ -876,6 +878,7 @@ static const struct nla_policy
>> br_port_policy[IFLA_BRPORT_MAX + 1] = {
>> [IFLA_BRPORT_NEIGH_SUPPRESS] = { .type = NLA_U8 },
>> [IFLA_BRPORT_ISOLATED] = { .type = NLA_U8 },
>> [IFLA_BRPORT_LOCKED] = { .type = NLA_U8 },
>> + [IFLA_BRPORT_MAB] = { .type = NLA_U8 },
>> [IFLA_BRPORT_BACKUP_PORT] = { .type = NLA_U32 },
>> [IFLA_BRPORT_MCAST_EHT_HOSTS_LIMIT] = { .type = NLA_U32 },
>> };
>> @@ -943,6 +946,10 @@ static int br_setport(struct net_bridge_port *p,
>> struct nlattr *tb[],
>> br_set_port_flag(p, tb, IFLA_BRPORT_NEIGH_SUPPRESS,
>> BR_NEIGH_SUPPRESS);
>> br_set_port_flag(p, tb, IFLA_BRPORT_ISOLATED, BR_ISOLATED);
>> br_set_port_flag(p, tb, IFLA_BRPORT_LOCKED, BR_PORT_LOCKED);
>> + br_set_port_flag(p, tb, IFLA_BRPORT_MAB, BR_PORT_MAB);
>> +
>> + if (!(p->flags & BR_PORT_LOCKED))
>> + p->flags &= ~BR_PORT_MAB;
>>
>> changed_mask = old_flags ^ p->flags;
>>
>> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
>> index 06e5f6faa431..048e4afbc5a0 100644
>> --- a/net/bridge/br_private.h
>> +++ b/net/bridge/br_private.h
>> @@ -251,7 +251,9 @@ enum {
>> BR_FDB_ADDED_BY_EXT_LEARN,
>> BR_FDB_OFFLOADED,
>> BR_FDB_NOTIFY,
>> - BR_FDB_NOTIFY_INACTIVE
>> + BR_FDB_NOTIFY_INACTIVE,
>> + BR_FDB_ENTRY_LOCKED,
>> + BR_FDB_BLACKHOLE,
>> };
>>
>> struct net_bridge_fdb_key {
>
> Cheers,
> Nik