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netdevsim: psp: rcu protect psp_dev reference

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There are two issues with the way psp_dev is used in nsim_do_psp():

1. There is no check for IS_ERR() on the peers psp_dev, before
   dereferencing.
2. The refcount on this psp_dev can be dropped by
   nsim_psp_rereg_write()

To fix this, we can make netdevsim's reference to its psp_dev an rcu
reference, and then nsim_do_psp() can read the fields it needs from an
rcu critical section.

Fixes: f857478d62 ("netdevsim: a basic test PSP implementation")
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260505-psd-rcu-v1-3-a8f69ec1ab96@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Daniel Zahka
2026-05-05 03:42:25 -07:00
committed by Jakub Kicinski
parent 24c96a4200
commit 07bdec3fc7
2 changed files with 36 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/netdevsim/netdevsim.h
View File

@@ -120,7 +120,7 @@ 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;

54
drivers/net/netdevsim/psp.c
View File

@@ -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;
}
@@ -209,10 +210,18 @@ static struct psp_dev_caps nsim_psp_caps = {
.assoc_drv_spc = sizeof(void *),
};
static 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);
}
@@ -220,7 +229,7 @@ void nsim_psp_uninit(struct netdevsim *ns)
{
debugfs_remove(ns->psp.rereg);
mutex_destroy(&ns->psp.rereg_lock);
__nsim_psp_uninit(ns);
__nsim_psp_uninit(ns, true);
}
static ssize_t
@@ -228,16 +237,23 @@ 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);
__nsim_psp_uninit(ns, false);
ns->psp.dev = psp_dev_create(ns->netdev, &nsim_psp_ops,
&nsim_psp_caps, ns);
err = PTR_ERR_OR_ZERO(ns->psp.dev);
psd = psp_dev_create(ns->netdev, &nsim_psp_ops, &nsim_psp_caps, ns);
if (IS_ERR(psd)) {
ret = PTR_ERR(psd);
goto out;
}
rcu_assign_pointer(ns->psp.dev, psd);
ret = count;
out:
mutex_unlock(&ns->psp.rereg_lock);
return err ?: count;
return ret;
}
static const struct file_operations nsim_psp_rereg_fops = {
@@ -250,13 +266,13 @@ 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;
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;
psd = psp_dev_create(ns->netdev, &nsim_psp_ops, &nsim_psp_caps, ns);
if (IS_ERR(psd))
return PTR_ERR(psd);
rcu_assign_pointer(ns->psp.dev, psd);
mutex_init(&ns->psp.rereg_lock);
ns->psp.rereg = debugfs_create_file("psp_rereg", 0200, ddir, ns,