[PATCH net v4 2/5] amt: reject a gateway Query or Data from 0.0.0.0 before a relay is learned

[PATCH net v4 2/5] amt: reject a gateway Query or Data from 0.0.0.0 before a relay is learned

[Omar Ramadan]

A gateway's amt_rcv() admits a Membership Query or Multicast Data message
when "saddr != remote_ip" is false.  remote_ip is 0 before discovery has
learned a relay (and is reset to 0 by amt_dev_open() and when discovery
gives up), so a packet whose source is 0.0.0.0 -- for example a
0.0.0.0 -> 255.255.255.255 broadcast delivered to the socket -- satisfies
0 != 0 and is accepted.  With the nonce freshly reset to 0, a spoofed
Query is then taken as genuine: it sets ready4/qi and the response MAC and
suppresses rediscovery until the discovery timeout, and a spoofed Data
message is injected the same way.

Reject both when no relay is learned: a 0 remote_ip must match nothing, so
guard the check with !remote_ip.  Discovery is unaffected -- Relay
Advertisements are validated against discovery_ip, not remote_ip.

Fixes: b9022b53adad ("amt: add control plane of amt interface")
Assisted-by: LLM
Signed-off-by: Omar Ramadan <omar@blockcast.net>
---
 drivers/net/amt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index 530650d..e9b1a45 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -2860,7 +2860,7 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
 			}
 			goto out;
 		case AMT_MSG_MULTICAST_DATA:
-			if (saddr != remote_ip) {
+			if (!remote_ip || saddr != remote_ip) {
 				netdev_dbg(amt->dev, "Invalid Relay IP\n");
 				err = true;
 				goto drop;
@@ -2871,7 +2871,7 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
 			else
 				goto out;
 		case AMT_MSG_MEMBERSHIP_QUERY:
-			if (saddr != remote_ip) {
+			if (!remote_ip || saddr != remote_ip) {
 				netdev_dbg(amt->dev, "Invalid Relay IP\n");
 				err = true;
 				goto drop;

Re: [PATCH net v4 2/5] amt: reject a gateway Query or Data from 0.0.0.0 before a relay is learned

[netdev-bot+sashiko]

Thank you for your contribution! Sashiko AI review found 1 potential
issue(s) to consider.

Critical: 0 · High: 1 · Medium: 0 · Low: 0

If you believe none of the issues are legitimate, please reply to each
issue of Medium severity or higher and explain why the AI is wrong.
If any of them are legitimate and you plan to respin, please let patchwork
know by including "pw-bot: cr" as a separate line at the end of your reply
(one such reply per series is enough).

- [High] The fix is incomplete.

--

amt: reject a gateway Query or Data from 0.0.0.0 before a relay is learned

This patch makes a gateway's amt_rcv() drop Membership Query and Multicast
Data messages while remote_ip is 0. Before, a packet from 0.0.0.0 matched
the unset remote_ip and was accepted. The commit message says that, with
the nonce reset to 0, such a spoofed Query would be taken as genuine.

> diff --git a/drivers/net/amt.c b/drivers/net/amt.c
> index 530650d5c19e9..e9b1a4585ce51 100644
> --- a/drivers/net/amt.c
> +++ b/drivers/net/amt.c

[ ... ]

> @@ -2871,7 +2871,7 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
>  			else
>  				goto out;
>  		case AMT_MSG_MEMBERSHIP_QUERY:
> -			if (saddr != remote_ip) {
> +			if (!remote_ip || saddr != remote_ip) {
>  				netdev_dbg(amt->dev, "Invalid Relay IP\n");
>  				err = true;
>  				goto drop;

[Severity: High]
Is this check early enough to give the result the commit message describes?
It runs in softirq, against a copy of remote_ip read at the top of
amt_rcv():

    remote_ip = READ_ONCE(amt->remote_ip);

The Query is then queued as AMT_EVENT_RECEIVE. It is handled later, in
amt_event_work()->amt_gw_rcv()->amt_membership_query_handler(). That
handler checks only the nonce. It does not look at remote_ip or
amt->status again:

    if (amtmq->nonce != amt->nonce)
        return true;

AMT_EVENT_SEND_REQUEST goes through the same FIFO. When discovery gives up,
amt_event_send_request() does this in the worker:

    if (amt->req_cnt > AMT_MAX_REQ_COUNT) {
        ...
        WRITE_ONCE(amt->remote_ip, 0);
        amt_update_gw_status(amt, AMT_STATUS_INIT, false);
        amt->req_cnt = 0;
        amt->nonce = 0;
        goto out;
    }

Consider a Query spoofed from the old relay address with nonce 0. It passes
the new check if it arrives while remote_ip still holds that address. This
can happen in two ways:

- it is queued behind a pending SEND_REQUEST event, or
- amt_rcv() read remote_ip just before the WRITE_ONCE().

If so, the worker would handle it after the reset:

amt_event_work()
  amt_event_send_request()       /* remote_ip = 0, nonce = 0, INIT */
  amt_gw_rcv()
    amt_membership_query_handler()
      amtmq->nonce == amt->nonce  /* 0 == 0 */
      WRITE_ONCE(amt->ready4, true);
      amt->mac = response_mac;
      amt->req_cnt = 0;
      amt->qi = ihv3->qqic;

The status then moves to AMT_STATUS_RECEIVED_QUERY. That makes
amt_event_send_discovery() skip discovery.

These are the effects the commit message says the patch prevents ("a
spoofed Query is then taken as genuine: it sets ready4/qi and the response
MAC and suppresses rediscovery"). Here they still happen with no relay
learned.

The give-up time is predictable. After an advertisement, unanswered
requests back off 2s/4s/8s/16s, so req_cnt passes AMT_MAX_REQ_COUNT about
30s later. Any host that can spoof the relay's source address could flood
Queries around that moment.

The later patches in this series do not appear to change
amt_membership_query_handler() or this event ordering.

Would it be better to check where the state is consumed? For example,
amt_membership_query_handler() could reject the Query unless amt->status is
AMT_STATUS_SENT_REQUEST or AMT_STATUS_RECEIVED_QUERY. Another option is to
require a non-zero remote_ip that matches ip_hdr(skb)->saddr, and possibly
to refuse the predictable nonce 0.

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261013175407.947606-1-omar%40blockcast.net

[PATCH net v4 2/5] amt: reject a gateway Query or Data from 0.0.0.0 before a relay is learned

[Omar Ramadan]

A gateway's amt_rcv() admits a Membership Query or Multicast Data message
when "saddr != remote_ip" is false.  remote_ip is 0 before discovery has
learned a relay (and is reset to 0 by amt_dev_open() and when discovery
gives up), so a packet whose source is 0.0.0.0 -- for example a
0.0.0.0 -> 255.255.255.255 broadcast delivered to the socket -- satisfies
0 != 0 and is accepted.  With the nonce freshly reset to 0, a spoofed
Query is then taken as genuine: it sets ready4/qi and the response MAC and
suppresses rediscovery until the discovery timeout, and a spoofed Data
message is injected the same way.

Reject both when no relay is learned: a 0 remote_ip must match nothing, so
guard the check with !remote_ip.  Discovery is unaffected -- Relay
Advertisements are validated against discovery_ip, not remote_ip.

Fixes: b9022b53adad ("amt: add control plane of amt interface")
Assisted-by: LLM

Signed-off-by: Omar Ramadan <omar@blockcast.net>
diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index b06916c..2e0d3aa 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -2413,6 +2413,10 @@ static bool amt_membership_query_handler(struct amt_dev *amt,
 	if (amtmq->reserved || amtmq->version)
 		return true;
 
+	/* A deferred query may outlive a relay address change. */
+	if (ip_hdr(skb)->saddr != READ_ONCE(amt->remote_ip))
+		return true;
+
 	if (amtmq->nonce != amt->nonce)
 		return true;
 
@@ -2882,7 +2886,7 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
 			}
 			goto out;
 		case AMT_MSG_MULTICAST_DATA:
-			if (saddr != remote_ip) {
+			if (!remote_ip || saddr != remote_ip) {
 				netdev_dbg(amt->dev, "Invalid Relay IP\n");
 				err = true;
 				goto drop;
@@ -2893,7 +2897,7 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
 			else
 				goto out;
 		case AMT_MSG_MEMBERSHIP_QUERY:
-			if (saddr != remote_ip) {
+			if (!remote_ip || saddr != remote_ip) {
 				netdev_dbg(amt->dev, "Invalid Relay IP\n");
 				err = true;
 				goto drop;
-- 
2.43.0

Re: [PATCH net v4 2/5] amt: reject a gateway Query or Data from 0.0.0.0 before a relay is learned

[netdev-bot+sashiko]

Thank you for your contribution! Sashiko AI review found 1 potential
issue(s) to consider.

Critical: 0 · High: 0 · Medium: 1 · Low: 0

If you believe none of the issues are legitimate, please reply to each
issue of Medium severity or higher and explain why the AI is wrong.
If any of them are legitimate and you plan to respin, please let patchwork
know by including "pw-bot: cr" as a separate line at the end of your reply
(one such reply per series is enough).

- [Medium] The commit message does not mention one of the three hunks,
  and that hunk seems to belong to a later patch in the series.

--

amt: reject a gateway Query or Data from 0.0.0.0 before a relay is learned

This commit adds a !remote_ip guard to the Membership Query and Multicast
Data source checks in amt_rcv(). With the guard, a gateway that has not
learned a relay no longer accepts these messages from 0.0.0.0. It also
adds a source re-check in amt_membership_query_handler().

> diff --git a/drivers/net/amt.c b/drivers/net/amt.c
> index b06916c7d57d5..2e0d3aae3759b 100644
> --- a/drivers/net/amt.c
> +++ b/drivers/net/amt.c
> @@ -2413,6 +2413,10 @@ static bool amt_membership_query_handler(struct amt_dev *amt,
>  	if (amtmq->reserved || amtmq->version)
>  		return true;
>  
> +	/* A deferred query may outlive a relay address change. */
> +	if (ip_hdr(skb)->saddr != READ_ONCE(amt->remote_ip))
> +		return true;
> +

[Severity: Medium]
The commit message doesn't seem to describe this hunk. It only covers the
remote_ip == 0 case in amt_rcv():

  "Reject both when no relay is learned: a 0 remote_ip must match
  nothing, so guard the check with !remote_ip."

This check covers a different case. amt_rcv() checks the Query against
remote_ip when the packet arrives, and the handler runs later from the
event worker:

amt_rcv()
    amt_queue_event(amt, AMT_EVENT_RECEIVE, skb)
...
amt_event_work()
    amt_gw_rcv()
        amt_membership_query_handler()

In that window, amt_advertisement_handler() can change remote_ip. It can
also be reset to 0 by amt_event_send_request(), amt_dev_open() or
amt_dev_stop(). With this hunk, a Query that passed the check when it was
queued is dropped if the relay address changed before the worker ran.

The later patch in the series, "amt: harden relay authentication and
teardown", says in its commit message:

  "A deferred gateway Query is accepted only if its relay address still
  matches the current relay"

However, that patch's diff doesn't touch amt_membership_query_handler(),
and it carries a different Fixes: tag (cbc21dc1cfe9).

Did this hunk end up in the wrong patch? This commit has
Fixes: b9022b53adad and is likely to be picked for stable. Could the hunk
move to the patch that describes it, or could this commit message mention
it?

>  	if (amtmq->nonce != amt->nonce)
>  		return true;
>  

[ ... ]

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261015220648.1545576-1-omar%40blockcast.net

[PATCH net v4 0/5] amt: relay tunnel lifetime, validation and request-path hardening

[Omar Ramadan]

This series hardens AMT relay tunnel lifetime, validates gateway input, and
keeps unauthenticated Requests from consuming relay state. The fixes were
found while reviewing the AMT IPv6 outer transport work; that work is not
included here.

I am using the existing IPv4 AMT relay and gateway implementation in a
multicast delivery network, where gateways on access networks send IGMP/MLD
membership state through a relay to reach downstream receivers. The fixes in
this series come from exercising that deployed control and data path; the
series does not claim to add the IPv6 outer transport.

The first patch closes the gc_wq re-arm use-after-free and makes teardown
safe for RCU readers and delayed group/source workers. The second rejects
Queries and Data from 0.0.0.0 before relay discovery and revalidates deferred
Queries. The third requires exactly four bytes for IPv4 netlink address
attributes. The fourth makes pre-Query drops visible, avoids counting
successful reports as drops, and uses concurrent-safe TX statistics. The
fifth keeps Requests stateless, authenticates Membership Updates before
allocation, keys state by address and port, bounds per-source admission, and
silently drops failed endpoint admission.

v5 changes:
- Defer group/source node freeing until their delayed work is synchronously
  cancelled, with separate GC links and owner-pointer invalidation.
- Preserve the original GMI expiry for Request-only intermediate tunnels.
- Document deferred Query revalidation and rewrite the patch 5 message to
  match its authentication and admission changes.
- Move the unauthenticated Request endpoint scan out of amt->lock and remove
  the ICMP response for failed verified tunnel allocation.
- Add the tunnel liveness checks to the lifetime fix and restore the dead
  locking comment.

Validation: GCC W=1 object builds with IPv6 enabled and disabled. The full
W=1 build is blocked by an unrelated existing unused-but-set warning in
net/netfilter/nft_compat.c; the AMT object itself is warning-free.

v4: https://lore.kernel.org/netdev/20261013175407.947606-1-omar@blockcast.net/
v3: https://lore.kernel.org/netdev/20261012125943.558629-1-omar@blockcast.net/
v2: https://lore.kernel.org/netdev/20261009201455.1904698-1-omar@blockcast.net/
v1: https://lore.kernel.org/netdev/20261008003606.3666617-1-omar@blockcast.net/

Assisted-by: LLM

Omar Ramadan (5):
  amt: fix use-after-free when a Membership Update re-arms a freed
    tunnel
  amt: reject a gateway Query or Data from 0.0.0.0 before a relay is
    learned
  amt: require an exact IPv4-sized IFLA_AMT_{LOCAL,DISCOVERY}_IP
  amt: make pre-query report drops visible
  amt: harden relay authentication and teardown

 drivers/net/amt.c | 550 +++++++++++++++++++++++++++++++++++-----------
 include/net/amt.h |  31 ++-
 2 files changed, 447 insertions(+), 134 deletions(-)

[PATCH net v4 1/5] amt: fix use-after-free when a Membership Update re-arms a freed tunnel

[Omar Ramadan]

amt_update_handler() refreshes a relay tunnel's garbage-collection timer
with mod_delayed_work() on a tunnel found by an RCU walk. A concurrent
amt_tunnel_expire() can unlink and free that tunnel while the Update path
still has the cached pointer, leaving gc_wq armed in freed memory.

Make amt_tunnel_expire() the only timeout-path freer. The Update path
records last_seen, and expire rechecks it under amt->lock before either
rearming or freeing the tunnel. Protect the dead state with tunnel->lock so
report handling cannot add multicast state after teardown begins. Device
stop marks tunnels dead, unlinks them with list_del_rcu(), synchronously
cancels
their work, and frees them after lockless readers have passed.

Apply the same lifetime rules to group and source timer work: mark nodes
dead
under tunnel->lock, keep RCU held while workers resolve their owners, defer
node freeing, and synchronously cancel each timer before freeing its owner.
Drain that deferred work before freeing a tunnel, and release the group
timer's device reference on every exit. A Request-only tunnel retains the
original GMI timeout; only an authenticated Membership Update refreshes
last_seen and uses the longer lifetime.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Assisted-by: LLM
---
 drivers/net/amt.c | 210 +++++++++++++++++++++++++++++++++++++++-------
 include/net/amt.h |  16 ++++
 2 files changed, 196 insertions(+), 30 deletions(-)

Signed-off-by: Omar Ramadan <omar@blockcast.net>
diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index b53f8ec..478bd85 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -38,6 +38,10 @@ static HLIST_HEAD(source_gc_list);
 /* Lock for source_gc_list */
 static spinlock_t source_gc_lock;
 static struct delayed_work source_gc_wq;
+static HLIST_HEAD(group_gc_list);
+/* Lock for group_gc_list */
+static spinlock_t group_gc_lock;
+static struct delayed_work group_gc_wq;
 static char *status_str[] = {
 	"AMT_STATUS_INIT",
 	"AMT_STATUS_SENT_DISCOVERY",
@@ -90,8 +94,9 @@ static void __amt_source_gc_work(void)
 	hlist_move_list(&source_gc_list, &gc_list);
 	spin_unlock_bh(&source_gc_lock);
 
-	hlist_for_each_entry_safe(snode, t, &gc_list, node) {
-		hlist_del_rcu(&snode->node);
+	hlist_for_each_entry_safe(snode, t, &gc_list, gc_node) {
+		cancel_delayed_work_sync(&snode->source_timer);
+		hlist_del_init(&snode->gc_node);
 		kfree_rcu(snode, rcu);
 	}
 }
@@ -106,6 +111,39 @@ static void amt_source_gc_work(struct work_struct *work)
 	spin_unlock_bh(&source_gc_lock);
 }
 
+static void __amt_group_gc_work(void)
+{
+	struct amt_group_node *gnode;
+	struct hlist_head gc_list;
+	struct hlist_node *t;
+
+	spin_lock_bh(&group_gc_lock);
+	hlist_move_list(&group_gc_list, &gc_list);
+	spin_unlock_bh(&group_gc_lock);
+
+	/* Group deletion queues all of its sources first.  Drain that queue
+	 * before freeing the group so a source callback cannot dereference it.
+	 */
+	cancel_delayed_work_sync(&source_gc_wq);
+	__amt_source_gc_work();
+
+	hlist_for_each_entry_safe(gnode, t, &gc_list, gc_node) {
+		cancel_delayed_work_sync(&gnode->group_timer);
+		hlist_del_init(&gnode->gc_node);
+		kfree_rcu(gnode, rcu);
+	}
+}
+
+static void amt_group_gc_work(struct work_struct *work)
+{
+	__amt_group_gc_work();
+
+	spin_lock_bh(&group_gc_lock);
+	mod_delayed_work(amt_wq, &group_gc_wq,
+			 msecs_to_jiffies(AMT_GC_INTERVAL));
+	spin_unlock_bh(&group_gc_lock);
+}
+
 static bool amt_addr_equal(union amt_addr *a, union amt_addr *b)
 {
 	return !memcmp(a, b, sizeof(union amt_addr));
@@ -215,9 +253,14 @@ static struct amt_group_node *amt_lookup_group(struct amt_tunnel_list *tunnel,
 
 static void amt_destroy_source(struct amt_source_node *snode)
 {
-	struct amt_group_node *gnode = snode->gnode;
+	struct amt_group_node *gnode;
 	struct amt_tunnel_list *tunnel;
 
+	if (READ_ONCE(snode->dead))
+		return;
+	WRITE_ONCE(snode->dead, true);
+	gnode = snode->gnode;
+
 	tunnel = gnode->tunnel_list;
 
 	if (!gnode->v6) {
@@ -238,8 +281,9 @@ static void amt_destroy_source(struct amt_source_node *snode)
 	hlist_del_init_rcu(&snode->node);
 	tunnel->nr_sources--;
 	gnode->nr_sources--;
+	RCU_INIT_POINTER(snode->gnode, NULL);
 	spin_lock_bh(&source_gc_lock);
-	hlist_add_head_rcu(&snode->node, &source_gc_list);
+	hlist_add_head(&snode->gc_node, &source_gc_list);
 	spin_unlock_bh(&source_gc_lock);
 }
 
@@ -249,6 +293,9 @@ static void amt_del_group(struct amt_dev *amt, struct amt_group_node *gnode)
 	struct hlist_node *t;
 	int i;
 
+	if (READ_ONCE(gnode->dead))
+		return;
+	WRITE_ONCE(gnode->dead, true);
 	if (cancel_delayed_work(&gnode->group_timer))
 		dev_put(amt->dev);
 	hlist_del_rcu(&gnode->node);
@@ -266,10 +313,10 @@ static void amt_del_group(struct amt_dev *amt, struct amt_group_node *gnode)
 		hlist_for_each_entry_safe(snode, t, &gnode->sources[i], node)
 			amt_destroy_source(snode);
 
-	/* tunnel->lock was acquired outside of amt_del_group()
-	 * But rcu_read_lock() was acquired too so It's safe.
-	 */
-	kfree_rcu(gnode, rcu);
+	RCU_INIT_POINTER(gnode->tunnel_list, NULL);
+	spin_lock_bh(&group_gc_lock);
+	hlist_add_head(&gnode->gc_node, &group_gc_list);
+	spin_unlock_bh(&group_gc_lock);
 }
 
 /* If a source timer expires with a router filter-mode for the group of
@@ -282,13 +329,28 @@ static void amt_source_work(struct work_struct *work)
 	struct amt_source_node *snode = container_of(to_delayed_work(work),
 						     struct amt_source_node,
 						     source_timer);
-	struct amt_group_node *gnode = snode->gnode;
-	struct amt_dev *amt = gnode->amt;
+	struct amt_group_node *gnode;
+	struct amt_dev *amt;
 	struct amt_tunnel_list *tunnel;
 
-	tunnel = gnode->tunnel_list;
-	spin_lock_bh(&tunnel->lock);
 	rcu_read_lock();
+	gnode = READ_ONCE(snode->gnode);
+	if (!gnode) {
+		rcu_read_unlock();
+		return;
+	}
+	amt = READ_ONCE(gnode->amt);
+	tunnel = READ_ONCE(gnode->tunnel_list);
+	if (!tunnel) {
+		rcu_read_unlock();
+		return;
+	}
+	spin_lock_bh(&tunnel->lock);
+	if (READ_ONCE(snode->dead) || READ_ONCE(gnode->dead)) {
+		spin_unlock_bh(&tunnel->lock);
+		rcu_read_unlock();
+		return;
+	}
 	if (gnode->filter_mode == MCAST_INCLUDE) {
 		amt_destroy_source(snode);
 		if (!gnode->nr_sources)
@@ -299,8 +361,8 @@ static void amt_source_work(struct work_struct *work)
 		 */
 		snode->status = AMT_SOURCE_STATUS_D_FWD;
 	}
-	rcu_read_unlock();
 	spin_unlock_bh(&tunnel->lock);
+	rcu_read_unlock();
 }
 
 static void amt_act_src(struct amt_tunnel_list *tunnel,
@@ -368,6 +430,7 @@ static struct amt_source_node *amt_alloc_snode(struct amt_group_node *gnode,
 	snode->status = AMT_SOURCE_STATUS_NONE;
 	snode->flags = AMT_SOURCE_NEW;
 	INIT_HLIST_NODE(&snode->node);
+	INIT_HLIST_NODE(&snode->gc_node);
 	INIT_DELAYED_WORK(&snode->source_timer, amt_source_work);
 
 	return snode;
@@ -403,26 +466,40 @@ static void amt_group_work(struct work_struct *work)
 	struct amt_group_node *gnode = container_of(to_delayed_work(work),
 						    struct amt_group_node,
 						    group_timer);
-	struct amt_tunnel_list *tunnel = gnode->tunnel_list;
-	struct amt_dev *amt = gnode->amt;
+	struct amt_tunnel_list *tunnel;
+	struct amt_dev *amt;
 	struct amt_source_node *snode;
 	bool delete_group = true;
 	struct hlist_node *t;
 	int i, buckets;
 
+	rcu_read_lock();
+	tunnel = READ_ONCE(gnode->tunnel_list);
+	amt = READ_ONCE(gnode->amt);
+	if (!tunnel) {
+		rcu_read_unlock();
+		dev_put(amt->dev);
+		return;
+	}
 	buckets = amt->hash_buckets;
 
 	spin_lock_bh(&tunnel->lock);
+	if (READ_ONCE(gnode->dead)) {
+		spin_unlock_bh(&tunnel->lock);
+		rcu_read_unlock();
+		dev_put(amt->dev);
+		return;
+	}
 	if (gnode->filter_mode == MCAST_INCLUDE) {
 		/* Not Used */
 		spin_unlock_bh(&tunnel->lock);
-		goto out;
+		rcu_read_unlock();
+		dev_put(amt->dev);
+		return;
 	}
 
-	rcu_read_lock();
-	for (i = 0; i < buckets; i++) {
-		hlist_for_each_entry_safe(snode, t,
-					  &gnode->sources[i], node) {
+	for (i = 0; i < buckets; i++)
+		hlist_for_each_entry_safe(snode, t, &gnode->sources[i], node) {
 			if (!delayed_work_pending(&snode->source_timer) ||
 			    snode->status == AMT_SOURCE_STATUS_D_FWD) {
 				amt_destroy_source(snode);
@@ -431,14 +508,12 @@ static void amt_group_work(struct work_struct *work)
 				snode->status = AMT_SOURCE_STATUS_FWD;
 			}
 		}
-	}
 	if (delete_group)
 		amt_del_group(amt, gnode);
 	else
 		gnode->filter_mode = MCAST_INCLUDE;
-	rcu_read_unlock();
 	spin_unlock_bh(&tunnel->lock);
-out:
+	rcu_read_unlock();
 	dev_put(amt->dev);
 }
 
@@ -479,6 +554,7 @@ static struct amt_group_node *amt_add_group(struct amt_dev *amt,
 	gnode->tunnel_list = tunnel;
 	gnode->filter_mode = MCAST_INCLUDE;
 	INIT_HLIST_NODE(&gnode->node);
+	INIT_HLIST_NODE(&gnode->gc_node);
 	INIT_DELAYED_WORK(&gnode->group_timer, amt_group_work);
 	for (i = 0; i < amt->hash_buckets; i++)
 		INIT_HLIST_HEAD(&gnode->sources[i]);
@@ -1328,14 +1404,41 @@ static void amt_tunnel_expire(struct work_struct *work)
 						      struct amt_tunnel_list,
 						      gc_wq);
 	struct amt_dev *amt = tunnel->amt;
+	unsigned long deadline;
 
 	spin_lock_bh(&amt->lock);
+	/* amt_dev_stop() has taken ownership of the teardown. */
+	if (READ_ONCE(tunnel->dead)) {
+		spin_unlock_bh(&amt->lock);
+		return;
+	}
+	/* A Membership Update may have refreshed the tunnel after this work
+	 * was queued.  Re-arm from last_seen rather than letting
+	 * amt_update_handler() re-arm gc_wq: this handler is then the only
+	 * context that frees the tunnel on the timeout path; amt_dev_stop()
+	 * still owns teardown during device shutdown.
+	 */
+	deadline = READ_ONCE(tunnel->last_seen);
+	if (!deadline)
+		deadline = jiffies;
+	else
+		deadline += msecs_to_jiffies(amt_gmi(amt)) * 3;
+	if (time_before(jiffies, deadline)) {
+		mod_delayed_work(amt_wq, &tunnel->gc_wq, deadline - jiffies);
+		spin_unlock_bh(&amt->lock);
+		return;
+	}
+	spin_lock_bh(&tunnel->lock);
+	WRITE_ONCE(tunnel->dead, true);
+	spin_unlock_bh(&tunnel->lock);
 	rcu_read_lock();
 	list_del_rcu(&tunnel->list);
 	amt->nr_tunnels--;
 	amt_clear_groups(tunnel);
 	rcu_read_unlock();
 	spin_unlock_bh(&amt->lock);
+	cancel_delayed_work_sync(&group_gc_wq);
+	__amt_group_gc_work();
 	kfree_rcu(tunnel, rcu);
 }
 
@@ -2494,9 +2597,13 @@ static bool amt_update_handler(struct amt_dev *amt, struct sk_buff *skb)
 		if (tunnel->ip4 == saddr) {
 			if ((nonce == tunnel->nonce &&
 			     response_mac == tunnel->mac)) {
-				mod_delayed_work(amt_wq, &tunnel->gc_wq,
-						 msecs_to_jiffies(amt_gmi(amt))
-								  * 3);
+				/* Refresh liveness only.  gc_wq is
+				 * re-armed by amt_tunnel_expire() itself
+				 * from last_seen, never from here, so this
+				 * cannot re-queue the work of a tunnel
+				 * that is being freed.
+				 */
+				WRITE_ONCE(tunnel->last_seen, jiffies);
 				goto report;
 			} else {
 				netdev_dbg(amt->dev, "Invalid MAC\n");
@@ -2522,6 +2629,10 @@ report:
 		}
 
 		spin_lock_bh(&tunnel->lock);
+		if (READ_ONCE(tunnel->dead)) {
+			spin_unlock_bh(&tunnel->lock);
+			return true;
+		}
 		amt_igmp_report_handler(amt, skb, tunnel);
 		spin_unlock_bh(&tunnel->lock);
 
@@ -2542,6 +2653,10 @@ report:
 		}
 
 		spin_lock_bh(&tunnel->lock);
+		if (READ_ONCE(tunnel->dead)) {
+			spin_unlock_bh(&tunnel->lock);
+			return true;
+		}
 		amt_mld_report_handler(amt, skb, tunnel);
 		spin_unlock_bh(&tunnel->lock);
 
@@ -3050,7 +3165,7 @@ static int amt_dev_open(struct net_device *dev)
 static int amt_dev_stop(struct net_device *dev)
 {
 	struct amt_dev *amt = netdev_priv(dev);
-	struct amt_tunnel_list *tunnel, *tmp;
+	struct amt_tunnel_list *tunnel;
 	struct sk_buff *skb;
 	struct sock *sk;
 	int i;
@@ -3079,11 +3194,38 @@ static int amt_dev_stop(struct net_device *dev)
 	amt->req_cnt = 0;
 	WRITE_ONCE(amt->remote_ip, 0);
 
-	list_for_each_entry_safe(tunnel, tmp, &amt->tunnel_list, list) {
-		list_del_rcu(&tunnel->list);
-		amt->nr_tunnels--;
+	/* Mark every tunnel dead first, so a concurrent amt_tunnel_expire()
+	 * sees ->dead and bails instead of freeing a tunnel in parallel; this
+	 * path is then the sole freer.
+	 */
+	spin_lock_bh(&amt->lock);
+	list_for_each_entry(tunnel, &amt->tunnel_list, list) {
+		spin_lock_bh(&tunnel->lock);
+		WRITE_ONCE(tunnel->dead, true);
+		spin_unlock_bh(&tunnel->lock);
+	}
+	spin_unlock_bh(&amt->lock);
+
+	/* Unlink one tunnel at a time with list_del_rcu() rather than splicing
+	 * the list onto a local head: a lockless reader walking tunnel_list
+	 * must always terminate at &amt->tunnel_list, never at a stack head.
+	 */
+	for (;;) {
+		spin_lock_bh(&amt->lock);
+		tunnel = list_first_entry_or_null(&amt->tunnel_list,
+						  struct amt_tunnel_list, list);
+		if (tunnel) {
+			list_del_rcu(&tunnel->list);
+			amt->nr_tunnels--;
+		}
+		spin_unlock_bh(&amt->lock);
+		if (!tunnel)
+			break;
+
 		cancel_delayed_work_sync(&tunnel->gc_wq);
 		amt_clear_groups(tunnel);
+		cancel_delayed_work_sync(&group_gc_wq);
+		__amt_group_gc_work();
 		kfree_rcu(tunnel, rcu);
 	}
 
@@ -3461,11 +3603,17 @@ static int __init amt_init(void)
 	}
 
 	spin_lock_init(&source_gc_lock);
+	spin_lock_init(&group_gc_lock);
 	spin_lock_bh(&source_gc_lock);
 	INIT_DELAYED_WORK(&source_gc_wq, amt_source_gc_work);
 	mod_delayed_work(amt_wq, &source_gc_wq,
 			 msecs_to_jiffies(AMT_GC_INTERVAL));
 	spin_unlock_bh(&source_gc_lock);
+	spin_lock_bh(&group_gc_lock);
+	INIT_DELAYED_WORK(&group_gc_wq, amt_group_gc_work);
+	mod_delayed_work(amt_wq, &group_gc_wq,
+			 msecs_to_jiffies(AMT_GC_INTERVAL));
+	spin_unlock_bh(&group_gc_lock);
 
 	return 0;
 
@@ -3485,6 +3633,8 @@ static void __exit amt_fini(void)
 	unregister_netdevice_notifier(&amt_notifier_block);
 	cancel_delayed_work_sync(&source_gc_wq);
 	__amt_source_gc_work();
+	cancel_delayed_work_sync(&group_gc_wq);
+	__amt_group_gc_work();
 	destroy_workqueue(amt_wq);
 }
 module_exit(amt_fini);
diff --git a/include/net/amt.h b/include/net/amt.h
index 2846dde..123725c 100644
--- a/include/net/amt.h
+++ b/include/net/amt.h
@@ -240,6 +240,16 @@ struct amt_tunnel_list {
 	u32			nr_sources;
 	enum amt_status		status;
 	struct delayed_work	gc_wq;
+	/* Last time this tunnel was refreshed.  gc_wq
+	 * re-arms itself from this rather than being re-armed by the Update
+	 * path, so the Update path cannot re-queue the work of a tunnel that
+	 * amt_tunnel_expire() is freeing.
+	 */
+	unsigned long		last_seen;
+	/* Set under amt->lock and tunnel->lock by whichever freer reaches the
+	 * tunnel first; the other then leaves it alone, so it is freed once.
+	 */
+	bool			dead;
 	__be16			source_port;
 	__be32			ip4;
 	__be32			nonce;
@@ -275,6 +285,7 @@ enum amt_source_status {
 /* protected by gnode->lock */
 struct amt_source_node {
 	struct hlist_node	node;
+	struct hlist_node	gc_node;
 	struct amt_group_node	*gnode;
 	struct delayed_work     source_timer;
 	union amt_addr		source_addr;
@@ -282,6 +293,8 @@ struct amt_source_node {
 #define AMT_SOURCE_OLD	0
 #define AMT_SOURCE_NEW	1
 	u8			flags;
+	/* Protected by gnode->tunnel_list->lock. */
+	bool			dead;
 	struct rcu_head		rcu;
 };
 
@@ -295,7 +308,10 @@ struct amt_group_node {
 	u32			nr_sources;
 	struct amt_tunnel_list	*tunnel_list;
 	struct hlist_node	node;
+	struct hlist_node	gc_node;
 	struct delayed_work     group_timer;
+	/* Protected by tunnel_list->lock. */
+	bool			dead;
 	struct rcu_head		rcu;
 	struct hlist_head	sources[];
 };

[PATCH net v4 2/5] amt: reject a gateway Query or Data from 0.0.0.0 before a relay is learned

[Omar Ramadan]

A gateway's amt_rcv() admits a Membership Query or Multicast Data message
when "saddr != remote_ip" is false. remote_ip is 0 before discovery has
learned a relay (and is reset to 0 by amt_dev_open() and when discovery
gives up), so a packet whose source is 0.0.0.0 would otherwise pass the
equality check and could spoof a Query or inject multicast data.

Reject both when no relay is learned: a 0 remote_ip must match nothing, so
guard the check with !remote_ip. A Query is queued before its event worker
processes it, so the relay address can also change in that window. Recheck
the packet source against the current remote_ip in the handler and discard
stale Queries. Discovery is unaffected because Relay Advertisements are
validated against discovery_ip, not remote_ip.

Fixes: b9022b53adad ("amt: add control plane of amt interface")
Assisted-by: LLM
---
 drivers/net/amt.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Signed-off-by: Omar Ramadan <omar@blockcast.net>
diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index 478bd85..c19e67a 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -2472,6 +2472,10 @@ static bool amt_membership_query_handler(struct amt_dev *amt,
 	if (amtmq->reserved || amtmq->version)
 		return true;
 
+	/* A deferred query may outlive a relay address change. */
+	if (ip_hdr(skb)->saddr != READ_ONCE(amt->remote_ip))
+		return true;
+
 	if (amtmq->nonce != amt->nonce)
 		return true;
 
@@ -2948,7 +2952,7 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
 			}
 			goto out;
 		case AMT_MSG_MULTICAST_DATA:
-			if (saddr != remote_ip) {
+			if (!remote_ip || saddr != remote_ip) {
 				netdev_dbg(amt->dev, "Invalid Relay IP\n");
 				err = true;
 				goto drop;
@@ -2959,7 +2963,7 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
 			else
 				goto out;
 		case AMT_MSG_MEMBERSHIP_QUERY:
-			if (saddr != remote_ip) {
+			if (!remote_ip || saddr != remote_ip) {
 				netdev_dbg(amt->dev, "Invalid Relay IP\n");
 				err = true;
 				goto drop;

[PATCH net v4 3/5] amt: require an exact IPv4-sized IFLA_AMT_{LOCAL,DISCOVERY}_IP

[Omar Ramadan]

The netlink policy for IFLA_AMT_LOCAL_IP and IFLA_AMT_DISCOVERY_IP is an
untyped entry with .len set to the size of an IPv4 address, which netlink
validation treats as a minimum length only.  Any longer payload passes,
and nla_get_in_addr() then reads just its first four bytes: an iproute2
that puts a 16-byte IPv6 literal in one of these IPv4 attributes turns
"2001:db8::" into 32.1.13.184, and the device is created with an address
the user never asked for.

Use NLA_POLICY_EXACT_LEN(sizeof(__be32)) for both, so every payload that
is not exactly four bytes long is refused with a standard extack instead
of being truncated.  The range check this expands to fails the attribute
even under the liberal parsing rtnetlink applies to IFLA_INFO_DATA.
amt_get_size() and amt_fill_info() already emit exactly four bytes for
these attributes.  IFLA_AMT_REMOTE_IP is only ever reported, never read
from a request, so it is left unchanged.

Fixes: b9022b53adad ("amt: add control plane of amt interface")
Assisted-by: LLM
---
 drivers/net/amt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Signed-off-by: Omar Ramadan <omar@blockcast.net>
diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index c19e67a..960a08d 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -3298,9 +3298,9 @@ static const struct nla_policy amt_policy[IFLA_AMT_MAX + 1] = {
 	[IFLA_AMT_RELAY_PORT]	= { .type = NLA_U16 },
 	[IFLA_AMT_GATEWAY_PORT]	= { .type = NLA_U16 },
 	[IFLA_AMT_LINK]		= { .type = NLA_U32 },
-	[IFLA_AMT_LOCAL_IP]	= { .len = sizeof_field(struct iphdr, daddr) },
+	[IFLA_AMT_LOCAL_IP]	= NLA_POLICY_EXACT_LEN(sizeof(__be32)),
 	[IFLA_AMT_REMOTE_IP]	= { .len = sizeof_field(struct iphdr, daddr) },
-	[IFLA_AMT_DISCOVERY_IP]	= { .len = sizeof_field(struct iphdr, daddr) },
+	[IFLA_AMT_DISCOVERY_IP]	= NLA_POLICY_EXACT_LEN(sizeof(__be32)),
 	[IFLA_AMT_MAX_TUNNELS]	= { .type = NLA_U32 },
 };
 

[PATCH net v4 4/5] amt: make pre-query report drops visible

[Omar Ramadan]

A gateway cannot forward an IGMP or MLD report until it has received the
relay's Membership Query for that family.  The Query supplies the
response MAC the Update echoes, so dropping an early report is required,
but doing so silently leaves operators with a dark multicast path and no
indication why the join never happened.

Emit a family-specific debug message before taking the drop path.

tx_dropped could not show these drops either: amt_dev_xmit() reaches the
same tx_dropped increment after amt_send_membership_update() has handed
the report to the tunnel, so in gateway mode every forwarded report was
also counted as a drop.  Return NETDEV_TX_OK directly once the report has
been sent, so tx_dropped counts only reports that were discarded.

The device is LLTX, so amt_dev_xmit() can run on several CPUs at once;
use DEV_STATS_INC() for its tx_dropped and tx_errors updates so
concurrent increments are not lost.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Assisted-by: LLM
---
 drivers/net/amt.c | 42 +++++++++++++++++++++++++-----------------
 1 file changed, 25 insertions(+), 17 deletions(-)

Signed-off-by: Omar Ramadan <omar@blockcast.net>
diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index 960a08d..f83afba 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -704,7 +704,7 @@ static void amt_send_discovery(struct amt_dev *amt)
 				   IPPROTO_UDP, 0,
 				   amt->stream_dev->ifindex);
 	if (IS_ERR(rt)) {
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 		goto out;
 	}
 
@@ -714,7 +714,7 @@ static void amt_send_discovery(struct amt_dev *amt)
 	skb = netdev_alloc_skb_ip_align(amt->dev, len);
 	if (!skb) {
 		ip_rt_put(rt);
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 		goto out;
 	}
 
@@ -759,7 +759,7 @@ static void amt_send_discovery(struct amt_dev *amt)
 	ip_send_check(iph);
 	err = ip_local_out(amt->net, sk, skb);
 	if (unlikely(net_xmit_eval(err)))
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 
 	amt_update_gw_status(amt, AMT_STATUS_SENT_DISCOVERY, true);
 out:
@@ -795,7 +795,7 @@ static void amt_send_request(struct amt_dev *amt, bool v6)
 				   IPPROTO_UDP, 0,
 				   amt->stream_dev->ifindex);
 	if (IS_ERR(rt)) {
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 		goto out;
 	}
 
@@ -805,7 +805,7 @@ static void amt_send_request(struct amt_dev *amt, bool v6)
 	skb = netdev_alloc_skb_ip_align(amt->dev, len);
 	if (!skb) {
 		ip_rt_put(rt);
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 		goto out;
 	}
 
@@ -852,7 +852,7 @@ static void amt_send_request(struct amt_dev *amt, bool v6)
 	ip_send_check(iph);
 	err = ip_local_out(amt->net, sk, skb);
 	if (unlikely(net_xmit_eval(err)))
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 
 out:
 	rcu_read_unlock();
@@ -874,7 +874,7 @@ static void amt_send_igmp_gq(struct amt_dev *amt,
 
 	skb_pull(skb, sizeof(struct ethhdr));
 	if (amt_send_membership_query(amt, skb, tunnel, false)) {
-		amt->dev->stats.tx_dropped++;
+		DEV_STATS_INC(amt->dev, tx_dropped);
 		kfree_skb(skb);
 	}
 }
@@ -918,7 +918,7 @@ static struct sk_buff *amt_build_mld_gq(struct amt_dev *amt)
 
 	if (ipv6_dev_get_saddr(amt->net, amt->dev, &ip6h->daddr, 0,
 			       &ip6h->saddr)) {
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 		kfree_skb(skb);
 		return NULL;
 	}
@@ -962,7 +962,7 @@ static void amt_send_mld_gq(struct amt_dev *amt, struct amt_tunnel_list *tunnel)
 
 	skb_pull(skb, sizeof(struct ethhdr));
 	if (amt_send_membership_query(amt, skb, tunnel, true)) {
-		amt->dev->stats.tx_dropped++;
+		DEV_STATS_INC(amt->dev, tx_dropped);
 		kfree_skb(skb);
 	}
 }
@@ -1312,7 +1312,7 @@ static netdev_tx_t amt_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 		group.ip6 = ipv6_hdr(skb)->daddr;
 #endif
 	} else {
-		dev->stats.tx_errors++;
+		DEV_STATS_INC(dev, tx_errors);
 		goto free;
 	}
 
@@ -1325,12 +1325,21 @@ static netdev_tx_t amt_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 		/* Gateway only passes IGMP/MLD packets */
 		if (!report)
 			goto free;
+		/* A validated report can only be forwarded after the relay's
+		 * family-specific Membership Query supplies the state echoed
+		 * by the Membership Update. Log this readiness failure before
+		 * the shared drop path accounts it.
+		 */
 		if ((!v6 && !READ_ONCE(amt->ready4)) ||
-		    (v6 && !READ_ONCE(amt->ready6)))
+		    (v6 && !READ_ONCE(amt->ready6))) {
+			netdev_dbg(dev, "drop %s report: waiting for Membership Query\n",
+				   v6 ? "MLD" : "IGMP");
 			goto free;
+		}
 		if (amt_send_membership_update(amt, skb,  v6))
 			goto free;
-		goto unlock;
+		/* Sent: the tunnel consumed the skb.  Not a drop. */
+		return NETDEV_TX_OK;
 	} else if (amt->mode == AMT_MODE_RELAY) {
 		if (!data)
 			goto free;
@@ -1359,8 +1368,7 @@ found:
 	return NETDEV_TX_OK;
 free:
 	dev_kfree_skb(skb);
-unlock:
-	dev->stats.tx_dropped++;
+	DEV_STATS_INC(dev, tx_dropped);
 	return NETDEV_TX_OK;
 }
 
@@ -2720,7 +2728,7 @@ static void amt_send_advertisement(struct amt_dev *amt, __be32 nonce,
 				   IPPROTO_UDP, 0,
 				   amt->stream_dev->ifindex);
 	if (IS_ERR(rt)) {
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 		goto out;
 	}
 
@@ -2730,7 +2738,7 @@ static void amt_send_advertisement(struct amt_dev *amt, __be32 nonce,
 	skb = netdev_alloc_skb_ip_align(amt->dev, len);
 	if (!skb) {
 		ip_rt_put(rt);
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 		goto out;
 	}
 
@@ -2776,7 +2784,7 @@ static void amt_send_advertisement(struct amt_dev *amt, __be32 nonce,
 	ip_send_check(iph);
 	err = ip_local_out(amt->net, sk, skb);
 	if (unlikely(net_xmit_eval(err)))
-		amt->dev->stats.tx_errors++;
+		DEV_STATS_INC(amt->dev, tx_errors);
 
 out:
 	rcu_read_unlock();

[PATCH net v4 5/5] amt: harden relay authentication and teardown

[Omar Ramadan]

An AMT Request has an unauthenticated, spoofable source address. Allocating
tunnel state from that path allowed spoofed Requests to consume tunnel
slots
or overwrite the nonce and MAC of an established gateway.

Keep Requests stateless by deriving the Query MAC from the source address,
source port, nonce, and current secret. Authenticate the Membership Update
before decapsulation or allocation, key verified state by the address/port
endpoint, enforce global and per-source limits, and silently reject an
endpoint that cannot be admitted. Retain four secret generations so a
gateway can renew its MAC across rotations.

Before a verified Update reaches the IGMP or MLD report handlers, recheck
tunnel liveness under tunnel->lock so it cannot add multicast state after
teardown has started.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Assisted-by: LLM
---
 drivers/net/amt.c | 300 +++++++++++++++++++++++++++++++++-------------
 include/net/amt.h |  21 ++--
 2 files changed, 228 insertions(+), 93 deletions(-)

Signed-off-by: Omar Ramadan <omar@blockcast.net>
diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index f83afba..faf3297 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -860,11 +860,16 @@ out:
 
 static bool amt_send_membership_query(struct amt_dev *amt,
 				      struct sk_buff *skb,
-				      struct amt_tunnel_list *tunnel,
+				      __be32 daddr, __be16 dport,
+				      __be32 nonce, u64 mac,
 				      bool v6);
 
-static void amt_send_igmp_gq(struct amt_dev *amt,
-			     struct amt_tunnel_list *tunnel)
+/* The destination is passed by value rather than as a tunnel: the requesting
+ * source is not authenticated yet and no tunnel state exists for it - see
+ * amt_request_handler().
+ */
+static void amt_send_igmp_gq(struct amt_dev *amt, __be32 daddr, __be16 dport,
+			     __be32 nonce, u64 mac)
 {
 	struct sk_buff *skb;
 
@@ -873,7 +878,8 @@ static void amt_send_igmp_gq(struct amt_dev *amt,
 		return;
 
 	skb_pull(skb, sizeof(struct ethhdr));
-	if (amt_send_membership_query(amt, skb, tunnel, false)) {
+	if (amt_send_membership_query(amt, skb, daddr, dport, nonce, mac,
+				      false)) {
 		DEV_STATS_INC(amt->dev, tx_dropped);
 		kfree_skb(skb);
 	}
@@ -952,7 +958,8 @@ static struct sk_buff *amt_build_mld_gq(struct amt_dev *amt)
 	return skb;
 }
 
-static void amt_send_mld_gq(struct amt_dev *amt, struct amt_tunnel_list *tunnel)
+static void amt_send_mld_gq(struct amt_dev *amt, __be32 daddr, __be16 dport,
+			    __be32 nonce, u64 mac)
 {
 	struct sk_buff *skb;
 
@@ -961,13 +968,15 @@ static void amt_send_mld_gq(struct amt_dev *amt, struct amt_tunnel_list *tunnel)
 		return;
 
 	skb_pull(skb, sizeof(struct ethhdr));
-	if (amt_send_membership_query(amt, skb, tunnel, true)) {
+	if (amt_send_membership_query(amt, skb, daddr, dport, nonce, mac,
+				      true)) {
 		DEV_STATS_INC(amt->dev, tx_dropped);
 		kfree_skb(skb);
 	}
 }
 #else
-static void amt_send_mld_gq(struct amt_dev *amt, struct amt_tunnel_list *tunnel)
+static void amt_send_mld_gq(struct amt_dev *amt, __be32 daddr, __be16 dport,
+			    __be32 nonce, u64 mac)
 {
 }
 #endif
@@ -1001,7 +1010,14 @@ static void amt_secret_work(struct work_struct *work)
 					   secret_wq);
 
 	spin_lock_bh(&amt->lock);
-	get_random_bytes(&amt->key, sizeof(siphash_key_t));
+	/* Keep three previous generations for a 180-240s MAC lifetime.
+	 * Its 180s floor exceeds the advertised QQIC (amt->qi, 125s),
+	 * allowing the gateway to renew its MAC with a periodic Request.
+	 */
+	amt->key[3] = amt->key[2];
+	amt->key[2] = amt->key[1];
+	amt->key[1] = amt->key[0];
+	get_random_bytes(&amt->key[0], sizeof(siphash_key_t));
 	spin_unlock_bh(&amt->lock);
 	mod_delayed_work(amt_wq, &amt->secret_wq,
 			 msecs_to_jiffies(AMT_SECRET_TIMEOUT));
@@ -1191,9 +1207,16 @@ static void amt_send_multicast_data(struct amt_dev *amt,
 			    0);
 }
 
+/* Send a Membership Query to a source that has not been authenticated yet.
+ *
+ * No per-source state exists at this point and none is created: the nonce and
+ * the keyed MAC are carried in the Query and recomputed from the Membership
+ * Update when it comes back, so everything this needs is passed by value.
+ */
 static bool amt_send_membership_query(struct amt_dev *amt,
 				      struct sk_buff *skb,
-				      struct amt_tunnel_list *tunnel,
+				      __be32 daddr, __be16 dport,
+				      __be32 nonce, u64 mac,
 				      bool v6)
 {
 	struct amt_header_membership_query *amtmq;
@@ -1214,13 +1237,13 @@ static bool amt_send_membership_query(struct amt_dev *amt,
 	skb_reset_inner_headers(skb);
 	memset(&fl4, 0, sizeof(struct flowi4));
 	fl4.flowi4_oif         = amt->stream_dev->ifindex;
-	fl4.daddr              = tunnel->ip4;
+	fl4.daddr              = daddr;
 	fl4.saddr              = amt->local_ip;
 	fl4.flowi4_dscp        = inet_dsfield_to_dscp(AMT_TOS);
 	fl4.flowi4_proto       = IPPROTO_UDP;
 	rt = ip_route_output_key(amt->net, &fl4);
 	if (IS_ERR(rt)) {
-		netdev_dbg(amt->dev, "no route to %pI4\n", &tunnel->ip4);
+		netdev_dbg(amt->dev, "no route to %pI4\n", &daddr);
 		return true;
 	}
 
@@ -1230,8 +1253,8 @@ static bool amt_send_membership_query(struct amt_dev *amt,
 	amtmq->reserved = 0;
 	amtmq->l	= 0;
 	amtmq->g	= 0;
-	amtmq->nonce	= tunnel->nonce;
-	amtmq->response_mac = tunnel->mac;
+	amtmq->nonce	= nonce;
+	amtmq->response_mac = mac;
 
 	if (!v6)
 		skb_set_inner_protocol(skb, htons(ETH_P_IP));
@@ -1244,11 +1267,10 @@ static bool amt_send_membership_query(struct amt_dev *amt,
 			    ip4_dst_hoplimit(&rt->dst),
 			    0,
 			    amt->relay_port,
-			    tunnel->source_port,
+			    dport,
 			    false,
 			    false,
 			    0);
-	amt_update_relay_status(tunnel, AMT_STATUS_SENT_QUERY, true);
 	return false;
 }
 
@@ -2576,16 +2598,106 @@ static bool amt_membership_query_handler(struct amt_dev *amt,
 	return false;
 }
 
+/* The tunnel of the gateway endpoint @saddr:@sport, or NULL. */
+static struct amt_tunnel_list *amt_tunnel_lookup(struct amt_dev *amt,
+						 __be32 saddr, __be16 sport)
+{
+	struct amt_tunnel_list *tunnel;
+
+	list_for_each_entry_rcu(tunnel, &amt->tunnel_list, list)
+		if (tunnel->ip4 == saddr && tunnel->source_port == sport)
+			return tunnel;
+	return NULL;
+}
+
+/* Look up the tunnel for a source whose Membership Update has already been
+ * authenticated, creating it on first contact.
+ *
+ * This is now the only place tunnel state is allocated, so amt->max_tunnels
+ * bounds the number of *verified* gateways rather than the number of
+ * unverified Requests anyone can send.  A fixed per-source cap additionally
+ * stops one verified source address from monopolising the table.
+ */
+static struct amt_tunnel_list *amt_tunnel_get_or_create(struct amt_dev *amt,
+							__be32 saddr,
+							__be16 sport)
+{
+	struct amt_tunnel_list *tunnel;
+	int per_src = 0;
+	int i;
+
+	tunnel = amt_tunnel_lookup(amt, saddr, sport);
+	if (tunnel)
+		return tunnel;
+
+	spin_lock_bh(&amt->lock);
+
+	/* Re-check under the lock in case a concurrent Update won the race, and
+	 * count how many tunnels this source already holds on the same walk.
+	 */
+	list_for_each_entry(tunnel, &amt->tunnel_list, list) {
+		if (tunnel->ip4 != saddr)
+			continue;
+		if (tunnel->source_port == sport) {
+			spin_unlock_bh(&amt->lock);
+			return tunnel;
+		}
+		per_src++;
+	}
+
+	if (amt->nr_tunnels >= amt->max_tunnels ||
+	    per_src >= AMT_MAX_TUNNELS_PER_SRC) {
+		spin_unlock_bh(&amt->lock);
+		return NULL;
+	}
+
+	if (!netif_running(amt->dev)) {
+		spin_unlock_bh(&amt->lock);
+		return NULL;
+	}
+
+	tunnel = kzalloc(sizeof(*tunnel) +
+			 (sizeof(struct hlist_head) * amt->hash_buckets),
+			 GFP_ATOMIC);
+	if (!tunnel) {
+		spin_unlock_bh(&amt->lock);
+		return NULL;
+	}
+
+	tunnel->source_port = sport;
+	tunnel->ip4 = saddr;
+	tunnel->amt = amt;
+	spin_lock_init(&tunnel->lock);
+	for (i = 0; i < amt->hash_buckets; i++)
+		INIT_HLIST_HEAD(&tunnel->groups[i]);
+
+	tunnel->last_seen = jiffies;
+	INIT_DELAYED_WORK(&tunnel->gc_wq, amt_tunnel_expire);
+	__amt_update_relay_status(tunnel, AMT_STATUS_RECEIVED_UPDATE, false);
+
+	/* Publish only once the entry is fully initialised. */
+	list_add_tail_rcu(&tunnel->list, &amt->tunnel_list);
+	amt->nr_tunnels++;
+	mod_delayed_work(amt_wq, &tunnel->gc_wq,
+			 msecs_to_jiffies(amt_gmi(amt)) * 3);
+	spin_unlock_bh(&amt->lock);
+
+	return tunnel;
+}
+
 static bool amt_update_handler(struct amt_dev *amt, struct sk_buff *skb)
 {
 	struct amt_header_membership_update *amtmu;
 	struct amt_tunnel_list *tunnel;
 	struct ethhdr *eth;
 	struct iphdr *iph;
-	int len, hdr_size;
+	siphash_key_t key[4];
+	int len, hdr_size, i;
 	u64 response_mac;
+	bool verified = false;
 	__be32 saddr;
 	__be32 nonce;
+	__be16 sport;
 
 	saddr = ip_hdr(skb)->saddr;
 
@@ -2599,34 +2711,51 @@ static bool amt_update_handler(struct amt_dev *amt, struct sk_buff *skb)
 
 	nonce = amtmu->nonce;
 	response_mac = amtmu->response_mac;
+	/* Snapshot the tunnel endpoint port before the encap is stripped. */
+	sport = udp_hdr(skb)->source;
 
-	if (iptunnel_pull_header(skb, hdr_size, skb->protocol, false))
-		return true;
+	/* Recompute the MAC handed out in the Membership Query.  Four live
+	 * secrets cover 180-240s, exceeding the advertised QQIC (amt->qi,
+	 * 125s), so a periodic Request can renew the MAC before it expires.
+	 * Authenticate before decapsulation or allocating tunnel state.
+	 */
+	spin_lock_bh(&amt->lock);
+	for (i = 0; i < ARRAY_SIZE(key); i++)
+		key[i] = amt->key[i];
+	spin_unlock_bh(&amt->lock);
 
-	skb_reset_network_header(skb);
+	for (i = 0; i < ARRAY_SIZE(key); i++) {
+		u64 mac = siphash_3u32((__force u32)saddr,
+				       (__force u32)sport,
+				       (__force u32)nonce,
+				       &key[i]) >> 16;
 
-	list_for_each_entry_rcu(tunnel, &amt->tunnel_list, list) {
-		if (tunnel->ip4 == saddr) {
-			if ((nonce == tunnel->nonce &&
-			     response_mac == tunnel->mac)) {
-				/* Refresh liveness only.  gc_wq is
-				 * re-armed by amt_tunnel_expire() itself
-				 * from last_seen, never from here, so this
-				 * cannot re-queue the work of a tunnel
-				 * that is being freed.
-				 */
-				WRITE_ONCE(tunnel->last_seen, jiffies);
-				goto report;
-			} else {
-				netdev_dbg(amt->dev, "Invalid MAC\n");
-				return true;
-			}
+		if (response_mac == mac) {
+			verified = true;
+			break;
 		}
 	}
 
-	return true;
+	if (!verified) {
+		netdev_dbg(amt->dev, "Invalid MAC\n");
+		return true;
+	}
+
+	tunnel = amt_tunnel_get_or_create(amt, saddr, sport);
+	if (!tunnel)
+		return true;
+
+	/* Refresh liveness only.  gc_wq is re-armed by amt_tunnel_expire()
+	 * itself from last_seen, never from here, so this cannot re-queue the
+	 * work of a tunnel that is being freed.
+	 */
+	WRITE_ONCE(tunnel->last_seen, jiffies);
+
+	if (iptunnel_pull_header(skb, hdr_size, skb->protocol, false))
+		return true;
+
+	skb_reset_network_header(skb);
 
-report:
 	if (!pskb_may_pull(skb, sizeof(*iph)))
 		return true;
 
@@ -2811,15 +2940,29 @@ static bool amt_discovery_handler(struct amt_dev *amt, struct sk_buff *skb)
 	return false;
 }
 
+/* Handle an AMT Relay Membership Request.
+ *
+ * The source of a Request is unauthenticated: it is a bare UDP datagram with a
+ * trivially spoofable source address.  Allocating tunnel state here let an
+ * attacker fill the table from spoofed addresses, and let one spoofed packet
+ * overwrite the nonce/MAC of an established tunnel and cut that gateway off.
+ *
+ * Nothing needs to be remembered at this point.  Every input to the keyed MAC
+ * is carried in the packet or is device state, so the MAC is generated here,
+ * echoed back by the gateway in its Membership Update, and recomputed and
+ * verified there - see amt_update_handler().  Tunnel state is created only once
+ * that verification succeeds.
+ */
 static bool amt_request_handler(struct amt_dev *amt, struct sk_buff *skb)
 {
 	struct amt_header_request *amtrh;
 	struct amt_tunnel_list *tunnel;
-	unsigned long long key;
 	struct udphdr *udph;
 	struct iphdr *iph;
+	siphash_key_t key;
+	bool full, have = false;
+	int per_src = 0;
 	u64 mac;
-	int i;
 
 	if (!pskb_may_pull(skb, sizeof(*udph) + sizeof(*amtrh)))
 		return true;
@@ -2831,59 +2974,41 @@ static bool amt_request_handler(struct amt_dev *amt, struct sk_buff *skb)
 	if (amtrh->reserved1 || amtrh->reserved2 || amtrh->version)
 		return true;
 
-	list_for_each_entry_rcu(tunnel, &amt->tunnel_list, list)
-		if (tunnel->ip4 == iph->saddr)
-			goto send;
-
-	spin_lock_bh(&amt->lock);
-	if (amt->nr_tunnels >= amt->max_tunnels) {
-		spin_unlock_bh(&amt->lock);
-		icmp_ndo_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_UNREACH, 0);
-		return true;
-	}
-
-	tunnel = kzalloc(sizeof(*tunnel) +
-			 (sizeof(struct hlist_head) * amt->hash_buckets),
-			 GFP_ATOMIC);
-	if (!tunnel) {
-		spin_unlock_bh(&amt->lock);
+	if (!netif_running(amt->dev) || !netif_running(amt->stream_dev))
 		return true;
-	}
-
-	tunnel->source_port = udph->source;
-	tunnel->ip4 = iph->saddr;
-
-	memcpy(&key, &tunnel->key, sizeof(unsigned long long));
-	tunnel->amt = amt;
-	spin_lock_init(&tunnel->lock);
-	for (i = 0; i < amt->hash_buckets; i++)
-		INIT_HLIST_HEAD(&tunnel->groups[i]);
-
-	INIT_DELAYED_WORK(&tunnel->gc_wq, amt_tunnel_expire);
 
-	list_add_tail_rcu(&tunnel->list, &amt->tunnel_list);
-	tunnel->key = amt->key;
-	__amt_update_relay_status(tunnel, AMT_STATUS_RECEIVED_REQUEST, true);
-	amt->nr_tunnels++;
-	mod_delayed_work(amt_wq, &tunnel->gc_wq,
-			 msecs_to_jiffies(amt_gmi(amt)));
+	/* Snapshot the secret and limits under the lock; keep the endpoint walk
+	 * out of the lock so spoofed Requests cannot serialize relay updates.
+	 */
+	spin_lock_bh(&amt->lock);
+	key = amt->key[0];
+	full = amt->nr_tunnels >= amt->max_tunnels;
 	spin_unlock_bh(&amt->lock);
 
-send:
-	tunnel->nonce = amtrh->nonce;
-	mac = siphash_3u32((__force u32)tunnel->ip4,
-			   (__force u32)tunnel->source_port,
-			   (__force u32)tunnel->nonce,
-			   &tunnel->key);
-	tunnel->mac = mac >> 16;
+	rcu_read_lock();
+	list_for_each_entry_rcu(tunnel, &amt->tunnel_list, list) {
+		if (tunnel->ip4 != iph->saddr)
+			continue;
+		per_src++;
+		if (tunnel->source_port == udph->source)
+			have = true;
+	}
+	rcu_read_unlock();
 
-	if (!netif_running(amt->dev) || !netif_running(amt->stream_dev))
+	/* Withhold the Query when a new endpoint cannot get a tunnel. */
+	if (!have && (full || per_src >= AMT_MAX_TUNNELS_PER_SRC))
 		return true;
 
+	mac = siphash_3u32((__force u32)iph->saddr,
+			   (__force u32)udph->source,
+			   (__force u32)amtrh->nonce,
+			   &key) >> 16;
 	if (!amtrh->p)
-		amt_send_igmp_gq(amt, tunnel);
+		amt_send_igmp_gq(amt, iph->saddr, udph->source, amtrh->nonce,
+				 mac);
 	else
-		amt_send_mld_gq(amt, tunnel);
+		amt_send_mld_gq(amt, iph->saddr, udph->source, amtrh->nonce,
+				 mac);
 
 	return false;
 }
@@ -3151,6 +3276,14 @@ static int amt_dev_open(struct net_device *dev)
 	enable_delayed_work(&amt->discovery_wq);
 	enable_delayed_work(&amt->req_wq);
 
+	/* Seed the keys before amt_socket_create() enables the encap receive
+	 * path, so a Request or Update that arrives immediately is never
+	 * verified against an all-zero (predictable) secret.
+	 */
+	spin_lock_bh(&amt->lock);
+	get_random_bytes(&amt->key, sizeof(amt->key));
+	spin_unlock_bh(&amt->lock);
+
 	err = amt_socket_create(amt);
 	if (err) {
 		disable_delayed_work(&amt->req_wq);
@@ -3161,7 +3294,6 @@ static int amt_dev_open(struct net_device *dev)
 	amt->req_cnt = 0;
 	WRITE_ONCE(amt->remote_ip, 0);
 	amt->nonce = 0;
-	get_random_bytes(&amt->key, sizeof(siphash_key_t));
 
 	amt->status = AMT_STATUS_INIT;
 	if (amt->mode == AMT_MODE_GATEWAY) {
diff --git a/include/net/amt.h b/include/net/amt.h
index 123725c..4acfc3d 100644
--- a/include/net/amt.h
+++ b/include/net/amt.h
@@ -242,20 +242,17 @@ struct amt_tunnel_list {
 	struct delayed_work	gc_wq;
 	/* Last time this tunnel was refreshed.  gc_wq
 	 * re-arms itself from this rather than being re-armed by the Update
-	 * path, so the Update path cannot re-queue the work of a tunnel that
-	 * amt_tunnel_expire() is freeing.
+	 * path, so the Update path cannot re-queue work for a tunnel that
+	 * amt_tunnel_expire() is freeing on the timeout path.
 	 */
 	unsigned long		last_seen;
 	/* Set under amt->lock and tunnel->lock by whichever freer reaches the
-	 * tunnel first; the other then leaves it alone, so it is freed once.
+	 * tunnel first;
+	 * the other then leaves it alone, so the tunnel is freed exactly once.
 	 */
 	bool			dead;
 	__be16			source_port;
 	__be32			ip4;
-	__be32			nonce;
-	siphash_key_t		key;
-	u64			mac:48,
-				reserved:16;
 	struct rcu_head		rcu;
 	struct hlist_head	groups[];
 };
@@ -341,8 +338,10 @@ struct amt_dev {
 	struct work_struct	event_wq;
 	/* AMT status */
 	enum amt_status		status;
-	/* Generated key */
-	siphash_key_t		key;
+	/* Current key and three previous generations keep MACs valid for
+	 * 180-240s, beyond the advertised QQIC (see amt_secret_work()).
+	 */
+	siphash_key_t		key[4];
 	struct sock	  __rcu *sk;
 	u32			max_groups;
 	u32			max_sources;
@@ -399,6 +398,10 @@ struct amt_dev {
 #define AMT_SECRET_TIMEOUT	60000
 #define IANA_AMT_UDP_PORT	2268
 #define AMT_MAX_TUNNELS         128
+/* Fixed per-source cap stops one verified source address from monopolising
+ * the AMT_MAX_TUNNELS-slot table.
+ */
+#define AMT_MAX_TUNNELS_PER_SRC 16
 #define AMT_MAX_REQS		128
 #define AMT_GW_HLEN (sizeof(struct iphdr) + \
 		     sizeof(struct udphdr) + \

Re: [PATCH net v4 0/5] amt: relay tunnel lifetime, validation and request-path hardening

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - Whether the issue was actually triggered, or is only theoretical
   (e.g. found by code inspection). If it was triggered please include
   the symptoms, like the stack trace or error messages.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.

Re: [PATCH net v4 0/5] amt: relay tunnel lifetime, validation and request-path hardening

[Omar Ramadan]

Thanks for the review. The findings are addressed in v5.

The group/source worker lifetime finding is valid. Taking rcu_read_lock()
inside a delayed-work callback was too late: the callback could be dequeued,
preempted, and its owner freed before it entered RCU. v5 gives source and
group nodes separate deferred-GC links, clears their owner pointers while
teardown holds tunnel->lock, and synchronously cancels each timer in the GC
worker before kfree_rcu(). The GC worker runs outside tunnel->lock, so it can
wait for a callback that is already running. Tunnel teardown drains the group
GC before freeing the tunnel. This also prevents a source callback from
running through a freed group or tunnel.

The tunnel->dead checks are now part of patch 1. amt_update_handler() checks
tunnel->dead under tunnel->lock before either report handler, and both tunnel
freers set it while holding the same lock. The deferred Query source check is
intentional and is now described by patch 2: a queued Query is revalidated
against the current remote_ip after relay changes or reset.

Request-only tunnels retain the original GMI timeout in the intermediate
lifetime fix. They do not stamp last_seen; only an authenticated Membership
Update refreshes it and receives the 3*GMI lifetime.

Patch 5's message now describes only stateless Requests, keyed Query MAC
authentication, endpoint admission, key generations, and the liveness guard.
The unauthenticated Request endpoint scan no longer holds amt->lock, and a
failed verified tunnel allocation is dropped silently rather than reflected
with ICMP. The dead comment again documents both locks.

pw-bot: cr