[PATCH AUTOSEL 6.18] netfilter: nfnetlink_queue: nfqnl_instance GFP_ATOMIC -> GFP_KERNEL_ACCOUNT allocation

[Sasha Levin <sashal@kernel.org>]

From: Scott Mitchell <scott.k.mitch1@gmail.com>

[ Upstream commit a4400a5b343d1bc4aa8f685608515413238e7ee2 ]

Currently, instance_create() uses GFP_ATOMIC because it's called while
holding instances_lock spinlock. This makes allocation more likely to
fail under memory pressure.

Refactor nfqnl_recv_config() to drop RCU lock after instance_lookup()
and peer_portid verification. A socket cannot simultaneously send a
message and close, so the queue owned by the sending socket cannot be
destroyed while processing its CONFIG message. This allows
instance_create() to allocate with GFP_KERNEL_ACCOUNT before taking
the spinlock.

Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Scott Mitchell <scott.k.mitch1@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Stable-dep-of: 936206e3f6ff ("netfilter: nfnetlink_queue: make hash table per queue")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Error: Failed to generate final synthesis

 net/netfilter/nfnetlink_queue.c | 75 +++++++++++++++------------------
 1 file changed, 34 insertions(+), 41 deletions(-)

diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index 0b96d20bacb73..a39d3b989063c 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -178,17 +178,9 @@ instance_create(struct nfnl_queue_net *q, u_int16_t queue_num, u32 portid)
 	unsigned int h;
 	int err;
 
-	spin_lock(&q->instances_lock);
-	if (instance_lookup(q, queue_num)) {
-		err = -EEXIST;
-		goto out_unlock;
-	}
-
-	inst = kzalloc(sizeof(*inst), GFP_ATOMIC);
-	if (!inst) {
-		err = -ENOMEM;
-		goto out_unlock;
-	}
+	inst = kzalloc(sizeof(*inst), GFP_KERNEL_ACCOUNT);
+	if (!inst)
+		return ERR_PTR(-ENOMEM);
 
 	inst->queue_num = queue_num;
 	inst->peer_portid = portid;
@@ -198,9 +190,15 @@ instance_create(struct nfnl_queue_net *q, u_int16_t queue_num, u32 portid)
 	spin_lock_init(&inst->lock);
 	INIT_LIST_HEAD(&inst->queue_list);
 
+	spin_lock(&q->instances_lock);
+	if (instance_lookup(q, queue_num)) {
+		err = -EEXIST;
+		goto out_unlock;
+	}
+
 	if (!try_module_get(THIS_MODULE)) {
 		err = -EAGAIN;
-		goto out_free;
+		goto out_unlock;
 	}
 
 	h = instance_hashfn(queue_num);
@@ -210,10 +208,9 @@ instance_create(struct nfnl_queue_net *q, u_int16_t queue_num, u32 portid)
 
 	return inst;
 
-out_free:
-	kfree(inst);
 out_unlock:
 	spin_unlock(&q->instances_lock);
+	kfree(inst);
 	return ERR_PTR(err);
 }
 
@@ -1604,7 +1601,8 @@ static int nfqnl_recv_config(struct sk_buff *skb, const struct nfnl_info *info,
 	struct nfqnl_msg_config_cmd *cmd = NULL;
 	struct nfqnl_instance *queue;
 	__u32 flags = 0, mask = 0;
-	int ret = 0;
+
+	WARN_ON_ONCE(!lockdep_nfnl_is_held(NFNL_SUBSYS_QUEUE));
 
 	if (nfqa[NFQA_CFG_CMD]) {
 		cmd = nla_data(nfqa[NFQA_CFG_CMD]);
@@ -1650,47 +1648,44 @@ static int nfqnl_recv_config(struct sk_buff *skb, const struct nfnl_info *info,
 		}
 	}
 
+	/* Lookup queue under RCU. After peer_portid check (or for new queue
+	 * in BIND case), the queue is owned by the socket sending this message.
+	 * A socket cannot simultaneously send a message and close, so while
+	 * processing this CONFIG message, nfqnl_rcv_nl_event() (triggered by
+	 * socket close) cannot destroy this queue. Safe to use without RCU.
+	 */
 	rcu_read_lock();
 	queue = instance_lookup(q, queue_num);
 	if (queue && queue->peer_portid != NETLINK_CB(skb).portid) {
-		ret = -EPERM;
-		goto err_out_unlock;
+		rcu_read_unlock();
+		return -EPERM;
 	}
+	rcu_read_unlock();
 
 	if (cmd != NULL) {
 		switch (cmd->command) {
 		case NFQNL_CFG_CMD_BIND:
-			if (queue) {
-				ret = -EBUSY;
-				goto err_out_unlock;
-			}
-			queue = instance_create(q, queue_num,
-						NETLINK_CB(skb).portid);
-			if (IS_ERR(queue)) {
-				ret = PTR_ERR(queue);
-				goto err_out_unlock;
-			}
+			if (queue)
+				return -EBUSY;
+			queue = instance_create(q, queue_num, NETLINK_CB(skb).portid);
+			if (IS_ERR(queue))
+				return PTR_ERR(queue);
 			break;
 		case NFQNL_CFG_CMD_UNBIND:
-			if (!queue) {
-				ret = -ENODEV;
-				goto err_out_unlock;
-			}
+			if (!queue)
+				return -ENODEV;
 			instance_destroy(q, queue);
-			goto err_out_unlock;
+			return 0;
 		case NFQNL_CFG_CMD_PF_BIND:
 		case NFQNL_CFG_CMD_PF_UNBIND:
 			break;
 		default:
-			ret = -ENOTSUPP;
-			goto err_out_unlock;
+			return -EOPNOTSUPP;
 		}
 	}
 
-	if (!queue) {
-		ret = -ENODEV;
-		goto err_out_unlock;
-	}
+	if (!queue)
+		return -ENODEV;
 
 	if (nfqa[NFQA_CFG_PARAMS]) {
 		struct nfqnl_msg_config_params *params =
@@ -1715,9 +1710,7 @@ static int nfqnl_recv_config(struct sk_buff *skb, const struct nfnl_info *info,
 		spin_unlock_bh(&queue->lock);
 	}
 
-err_out_unlock:
-	rcu_read_unlock();
-	return ret;
+	return 0;
 }
 
 static const struct nfnl_callback nfqnl_cb[NFQNL_MSG_MAX] = {
-- 
2.53.0