Merge branch 'netdevsim-psp-fix-init-and-uninit-bugs'

Daniel Zahka says:

====================
netdevsim: psp: fix init and uninit bugs

This series has three fixes. The first is a straightforward NULL
pointer dereference that is reachable by creating and destroying some
vfs on a kernel with INET_PSP enabled.

The last two patches deal with nsim_psp_rereg_write(), which is a
debugfs handler that reregisters netdevsim's psp_dev without
aquiescing and disabling tx/rx processing. This was added to enable
some tests in psp.py where a psp device is unregistered while it still
referenced by tcp socket state.

There are two issues with this code:
1. Calls to nsim_psp_uninit() are not properly serialized
2. netdevsim's psp_dev refcount can be released while nsim_do_psp() is
   reading from it.
====================

Link: https://patch.msgid.link/20260505-psd-rcu-v1-0-a8f69ec1ab96@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 51 insertions, 21 deletions

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index a05af192caf3..a750768912b5 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -1182,7 +1182,8 @@ void nsim_destroy(struct netdevsim *ns)
 		unregister_netdevice_notifier_dev_net(ns->netdev, &ns->nb,
 						      &ns->nn);
 
-	nsim_psp_uninit(ns);
+	if (nsim_dev_port_is_pf(ns->nsim_dev_port))
+		nsim_psp_uninit(ns);
 
 	rtnl_lock();
 	peer = rtnl_dereference(ns->peer);
diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
index 7e129dddbbe7..d909c4160ea1 100644
--- a/drivers/net/netdevsim/netdevsim.h
+++ b/drivers/net/netdevsim/netdevsim.h
@@ -120,7 +120,9 @@ struct netdevsim {
 		u64_stats_t tx_packets;
 		u64_stats_t tx_bytes;
 		struct u64_stats_sync syncp;
-		struct psp_dev *dev;
+		struct psp_dev __rcu *dev;
+		struct dentry *rereg;
+		struct mutex rereg_lock;
 		u32 spi;
 		u32 assoc_cnt;
 	} psp;
diff --git a/drivers/net/netdevsim/psp.c b/drivers/net/netdevsim/psp.c
index 0b4d717253b0..6936ecb8173e 100644
--- a/drivers/net/netdevsim/psp.c
+++ b/drivers/net/netdevsim/psp.c
@@ -19,6 +19,7 @@ nsim_do_psp(struct sk_buff *skb, struct netdevsim *ns,
 	    struct netdevsim *peer_ns, struct skb_ext **psp_ext)
 {
 	enum skb_drop_reason rc = 0;
+	struct psp_dev *peer_psd;
 	struct psp_assoc *pas;
 	struct net *net;
 	void **ptr;
@@ -48,7 +49,8 @@ nsim_do_psp(struct sk_buff *skb, struct netdevsim *ns,
 	}
 
 	/* Now pretend we just received this frame */
-	if (peer_ns->psp.dev->config.versions & (1 << pas->version)) {
+	peer_psd = rcu_dereference(peer_ns->psp.dev);
+	if (peer_psd && peer_psd->config.versions & (1 << pas->version)) {
 		bool strip_icv = false;
 		u8 generation;
 
@@ -61,8 +63,7 @@ nsim_do_psp(struct sk_buff *skb, struct netdevsim *ns,
 
 		skb_ext_reset(skb);
 		skb->mac_len = ETH_HLEN;
-		if (psp_dev_rcv(skb, peer_ns->psp.dev->id, generation,
-				strip_icv)) {
+		if (psp_dev_rcv(skb, peer_psd->id, generation, strip_icv)) {
 			rc = SKB_DROP_REASON_PSP_OUTPUT;
 			goto out_unlock;
 		}
@@ -209,26 +210,50 @@ static struct psp_dev_caps nsim_psp_caps = {
 	.assoc_drv_spc = sizeof(void *),
 };
 
-void nsim_psp_uninit(struct netdevsim *ns)
+static void __nsim_psp_uninit(struct netdevsim *ns, bool teardown)
 {
-	if (!IS_ERR(ns->psp.dev))
-		psp_dev_unregister(ns->psp.dev);
+	struct psp_dev *psd;
+
+	psd = rcu_dereference_protected(ns->psp.dev,
+					teardown ||
+					lockdep_is_held(&ns->psp.rereg_lock));
+	if (psd) {
+		rcu_assign_pointer(ns->psp.dev, NULL);
+		synchronize_rcu();
+		psp_dev_unregister(psd);
+	}
 	WARN_ON(ns->psp.assoc_cnt);
 }
 
+void nsim_psp_uninit(struct netdevsim *ns)
+{
+	debugfs_remove(ns->psp.rereg);
+	mutex_destroy(&ns->psp.rereg_lock);
+	__nsim_psp_uninit(ns, true);
+}
+
 static ssize_t
 nsim_psp_rereg_write(struct file *file, const char __user *data, size_t count,
 		     loff_t *ppos)
 {
 	struct netdevsim *ns = file->private_data;
-	int err;
+	struct psp_dev *psd;
+	ssize_t ret;
+
+	mutex_lock(&ns->psp.rereg_lock);
+	__nsim_psp_uninit(ns, false);
 
-	nsim_psp_uninit(ns);
+	psd = psp_dev_create(ns->netdev, &nsim_psp_ops, &nsim_psp_caps, ns);
+	if (IS_ERR(psd)) {
+		ret = PTR_ERR(psd);
+		goto out;
+	}
 
-	ns->psp.dev = psp_dev_create(ns->netdev, &nsim_psp_ops,
-				     &nsim_psp_caps, ns);
-	err = PTR_ERR_OR_ZERO(ns->psp.dev);
-	return err ?: count;
+	rcu_assign_pointer(ns->psp.dev, psd);
+	ret = count;
+out:
+	mutex_unlock(&ns->psp.rereg_lock);
+	return ret;
 }
 
 static const struct file_operations nsim_psp_rereg_fops = {
@@ -241,14 +266,16 @@ static const struct file_operations nsim_psp_rereg_fops = {
 int nsim_psp_init(struct netdevsim *ns)
 {
 	struct dentry *ddir = ns->nsim_dev_port->ddir;
-	int err;
+	struct psp_dev *psd;
+
+	psd = psp_dev_create(ns->netdev, &nsim_psp_ops, &nsim_psp_caps, ns);
+	if (IS_ERR(psd))
+		return PTR_ERR(psd);
 
-	ns->psp.dev = psp_dev_create(ns->netdev, &nsim_psp_ops,
-				     &nsim_psp_caps, ns);
-	err = PTR_ERR_OR_ZERO(ns->psp.dev);
-	if (err)
-		return err;
+	rcu_assign_pointer(ns->psp.dev, psd);
 
-	debugfs_create_file("psp_rereg", 0200, ddir, ns, &nsim_psp_rereg_fops);
+	mutex_init(&ns->psp.rereg_lock);
+	ns->psp.rereg = debugfs_create_file("psp_rereg", 0200, ddir, ns,
+					    &nsim_psp_rereg_fops);
 	return 0;
 }