Merge branch 'with-a-mutex'

Eric Dumazet says:

====================
net: atm: protect dev_lec[] with a mutex

Based on an initial syzbot report.

First patch is adding lec_mutex to address the report.

Second patch protects /proc/net/atm/lec operations.

We probably should delete this driver, it seems quite broken.
====================

Link: https://patch.msgid.link/20250618140844.1686882-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/atm/lec.c

@@ -124,6 +124,7 @@ static unsigned char bus_mac[ETH_ALEN] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
 
 /* Device structures */
 static struct net_device *dev_lec[MAX_LEC_ITF];
+static DEFINE_MUTEX(lec_mutex);
 
 #if IS_ENABLED(CONFIG_BRIDGE)
 static void lec_handle_bridge(struct sk_buff *skb, struct net_device *dev)
@@ -685,6 +686,7 @@ static int lec_vcc_attach(struct atm_vcc *vcc, void __user *arg)
 	int bytes_left;
 	struct atmlec_ioc ioc_data;
 
+	lockdep_assert_held(&lec_mutex);
 	/* Lecd must be up in this case */
 	bytes_left = copy_from_user(&ioc_data, arg, sizeof(struct atmlec_ioc));
 	if (bytes_left != 0)
@@ -710,6 +712,7 @@ static int lec_vcc_attach(struct atm_vcc *vcc, void __user *arg)
 
 static int lec_mcast_attach(struct atm_vcc *vcc, int arg)
 {
+	lockdep_assert_held(&lec_mutex);
 	if (arg < 0 || arg >= MAX_LEC_ITF)
 		return -EINVAL;
 	arg = array_index_nospec(arg, MAX_LEC_ITF);
@@ -725,6 +728,7 @@ static int lecd_attach(struct atm_vcc *vcc, int arg)
 	int i;
 	struct lec_priv *priv;
 
+	lockdep_assert_held(&lec_mutex);
 	if (arg < 0)
 		arg = 0;
 	if (arg >= MAX_LEC_ITF)
@@ -742,6 +746,7 @@ static int lecd_attach(struct atm_vcc *vcc, int arg)
 		snprintf(dev_lec[i]->name, IFNAMSIZ, "lec%d", i);
 		if (register_netdev(dev_lec[i])) {
 			free_netdev(dev_lec[i]);
+			dev_lec[i] = NULL;
 			return -EINVAL;
 		}
 
@@ -904,7 +909,6 @@ static void *lec_itf_walk(struct lec_state *state, loff_t *l)
 	v = (dev && netdev_priv(dev)) ?
 		lec_priv_walk(state, l, netdev_priv(dev)) : NULL;
 	if (!v && dev) {
-		dev_put(dev);
 		/* Partial state reset for the next time we get called */
 		dev = NULL;
 	}
@@ -928,6 +932,7 @@ static void *lec_seq_start(struct seq_file *seq, loff_t *pos)
 {
 	struct lec_state *state = seq->private;
 
+	mutex_lock(&lec_mutex);
 	state->itf = 0;
 	state->dev = NULL;
 	state->locked = NULL;
@@ -945,8 +950,9 @@ static void lec_seq_stop(struct seq_file *seq, void *v)
 	if (state->dev) {
 		spin_unlock_irqrestore(&state->locked->lec_arp_lock,
 				       state->flags);
-		dev_put(state->dev);
+		state->dev = NULL;
 	}
+	mutex_unlock(&lec_mutex);
 }
 
 static void *lec_seq_next(struct seq_file *seq, void *v, loff_t *pos)
@@ -1003,6 +1009,7 @@ static int lane_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 		return -ENOIOCTLCMD;
 	}
 
+	mutex_lock(&lec_mutex);
 	switch (cmd) {
 	case ATMLEC_CTRL:
 		err = lecd_attach(vcc, (int)arg);
@@ -1017,6 +1024,7 @@ static int lane_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 		break;
 	}
 
+	mutex_unlock(&lec_mutex);
 	return err;
 }