Subject: Re: [PATCH net] net: dsa: fix panic when port leaves a bridge

From: Vladimir Oltean <[email-masked]>
Date: Mon, 14 Mar 2022 15:41:00 +0000

Hi Marek,

On Mon, Mar 14, 2022 at 04:34:10PM +0100, Marek Behún wrote:
> Fix a data structure breaking / NULL-pointer dereference in
> dsa_switch_bridge_leave().
> 
> When a DSA port leaves a bridge, dsa_switch_bridge_leave() is called by
> notifier for every DSA switch that contains ports that are in the
> bridge.
> 
> But the part of the code that unsets vlan_filtering expects that the ds
> argument refers to the same switch that contains the leaving port.
> 
> This leads to various problems, including a NULL pointer dereference,
> which was observed on Turris MOX with 2 switches (one with 8 user ports
> and another with 4 user ports).
> 
> Thus we need to move the vlan_filtering change code to the non-crosschip
> branch.
> 
> Fixes: d371b7c92d190 ("net: dsa: Unset vlan_filtering when ports leave the bridge")
> Reported-by: Jan Bětík <[email-masked]>
> Signed-off-by: Marek Behún <[email-masked]>
> ---
>  net/dsa/switch.c | 97 +++++++++++++++++++++++++++---------------------
>  1 file changed, 55 insertions(+), 42 deletions(-)
> 
> diff --git a/net/dsa/switch.c b/net/dsa/switch.c
> index e3c7d2627a61..38afb1e8fcb7 100644
> --- a/net/dsa/switch.c
> +++ b/net/dsa/switch.c
> @@ -123,9 +123,61 @@ static int dsa_switch_bridge_leave(struct dsa_switch *ds,
>  	struct dsa_port *dp;
>  	int err;
>  
> -	if (dst->index == info->tree_index && ds->index == info->sw_index &&
> -	    ds->ops->port_bridge_leave)
> -		ds->ops->port_bridge_leave(ds, info->port, info->bridge);
> +	if (dst->index == info->tree_index && ds->index == info->sw_index) {
> +		if (ds->ops->port_bridge_leave)
> +			ds->ops->port_bridge_leave(ds, info->port,
> +						   info->bridge);
> +
> +		/* This function is called by the notifier for every DSA switch
> +		 * that has ports in the bridge we are leaving, but vlan
> +		 * filtering on the port should be changed only once. Since the
> +		 * code expects that ds is the switch containing the leaving
> +		 * port, the following code must not be called in the crosschip
> +		 * branch, only here.
> +		 */
> +
> +		if (ds->needs_standalone_vlan_filtering &&
> +		    !br_vlan_enabled(info->bridge.dev)) {
> +			change_vlan_filtering = true;
> +			vlan_filtering = true;
> +		} else if (!ds->needs_standalone_vlan_filtering &&
> +			   br_vlan_enabled(info->bridge.dev)) {
> +			change_vlan_filtering = true;
> +			vlan_filtering = false;
> +		}
> +
> +		/* If the bridge was vlan_filtering, the bridge core doesn't
> +		 * trigger an event for changing vlan_filtering setting upon
> +		 * slave ports leaving it. That is a good thing, because that
> +		 * lets us handle it and also handle the case where the switch's
> +		 * vlan_filtering setting is global (not per port). When that
> +		 * happens, the correct moment to trigger the vlan_filtering
> +		 * callback is only when the last port leaves the last
> +		 * VLAN-aware bridge.
> +		 */
> +		if (change_vlan_filtering && ds->vlan_filtering_is_global) {
> +			dsa_switch_for_each_port(dp, ds) {
> +				struct net_device *br =
> +					dsa_port_bridge_dev_get(dp);
> +
> +				if (br && br_vlan_enabled(br)) {
> +					change_vlan_filtering = false;
> +					break;
> +				}
> +			}
> +		}
> +
> +		if (change_vlan_filtering) {
> +			err = dsa_port_vlan_filtering(dsa_to_port(ds,
> +								  info->port),
> +						      vlan_filtering, &extack);
> +			if (extack._msg)
> +				dev_err(ds->dev, "port %d: %s\n", info->port,
> +					extack._msg);
> +			if (err && err != -EOPNOTSUPP)
> +				return err;
> +		}
> +	}
>  
>  	if ((dst->index != info->tree_index || ds->index != info->sw_index) &&
>  	    ds->ops->crosschip_bridge_leave)
> @@ -133,45 +185,6 @@ static int dsa_switch_bridge_leave(struct dsa_switch *ds,
>  						info->sw_index, info->port,
>  						info->bridge);
>  
> -	if (ds->needs_standalone_vlan_filtering &&
> -	    !br_vlan_enabled(info->bridge.dev)) {
> -		change_vlan_filtering = true;
> -		vlan_filtering = true;
> -	} else if (!ds->needs_standalone_vlan_filtering &&
> -		   br_vlan_enabled(info->bridge.dev)) {
> -		change_vlan_filtering = true;
> -		vlan_filtering = false;
> -	}
> -
> -	/* If the bridge was vlan_filtering, the bridge core doesn't trigger an
> -	 * event for changing vlan_filtering setting upon slave ports leaving
> -	 * it. That is a good thing, because that lets us handle it and also
> -	 * handle the case where the switch's vlan_filtering setting is global
> -	 * (not per port). When that happens, the correct moment to trigger the
> -	 * vlan_filtering callback is only when the last port leaves the last
> -	 * VLAN-aware bridge.
> -	 */
> -	if (change_vlan_filtering && ds->vlan_filtering_is_global) {
> -		dsa_switch_for_each_port(dp, ds) {
> -			struct net_device *br = dsa_port_bridge_dev_get(dp);
> -
> -			if (br && br_vlan_enabled(br)) {
> -				change_vlan_filtering = false;
> -				break;
> -			}
> -		}
> -	}
> -
> -	if (change_vlan_filtering) {
> -		err = dsa_port_vlan_filtering(dsa_to_port(ds, info->port),
> -					      vlan_filtering, &extack);
> -		if (extack._msg)
> -			dev_err(ds->dev, "port %d: %s\n", info->port,
> -				extack._msg);
> -		if (err && err != -EOPNOTSUPP)
> -			return err;
> -	}
> -
>  	return dsa_tag_8021q_bridge_leave(ds, info);
>  }
>  
> -- 
> 2.34.1
>

I had this patch in my tree for a while, moving the VLAN filtering reset
logic where it should really stay. Could you please check that this
placement fixes the NULL pointer dereferences too, and if it does,
combine my change with your commit message/authorship and resend?

From 5e0bbf38d35ceab0fba3f16f832bdbb7c127c167 Mon Sep 17 00:00:00 2001
From: Vladimir Oltean <[email-masked]>
Date: Mon, 21 Feb 2022 20:31:27 +0200
Subject: [PATCH] net: dsa: move reset of VLAN filtering to
 dsa_port_switchdev_unsync_attrs

In dsa_port_switchdev_unsync_attrs() there is a comment that resetting
the VLAN filtering isn't done where it is expected. And since commit
108dc8741c20 ("net: dsa: Avoid cross-chip syncing of VLAN filtering"),
there is no reason to handle this in switch.c either.

Therefore, move the logic to port.c, and adapt it slightly to the data
structures and naming conventions from there.

Signed-off-by: Vladimir Oltean <[email-masked]>
---
 net/dsa/port.c   | 60 +++++++++++++++++++++++++++++++++++++++++++++---
 net/dsa/switch.c | 58 ----------------------------------------------
 2 files changed, 57 insertions(+), 61 deletions(-)

diff --git a/net/dsa/port.c b/net/dsa/port.c
index 58291df14cdb..d280c7a3af7b 100644
--- a/net/dsa/port.c
+++ b/net/dsa/port.c
@@ -172,6 +172,59 @@ void dsa_port_disable(struct dsa_port *dp)
 	rtnl_unlock();
 }
 
+static void dsa_port_reset_vlan_filtering(struct dsa_port *dp,
+					  struct dsa_bridge bridge)
+{
+	struct netlink_ext_ack extack = {0};
+	bool change_vlan_filtering = false;
+	struct dsa_switch *ds = dp->ds;
+	bool vlan_filtering;
+	int err;
+
+	if (ds->needs_standalone_vlan_filtering &&
+	    !br_vlan_enabled(bridge.dev)) {
+		change_vlan_filtering = true;
+		vlan_filtering = true;
+	} else if (!ds->needs_standalone_vlan_filtering &&
+		   br_vlan_enabled(bridge.dev)) {
+		change_vlan_filtering = true;
+		vlan_filtering = false;
+	}
+
+	/* If the bridge was vlan_filtering, the bridge core doesn't trigger an
+	 * event for changing vlan_filtering setting upon slave ports leaving
+	 * it. That is a good thing, because that lets us handle it and also
+	 * handle the case where the switch's vlan_filtering setting is global
+	 * (not per port). When that happens, the correct moment to trigger the
+	 * vlan_filtering callback is only when the last port leaves the last
+	 * VLAN-aware bridge.
+	 */
+	if (change_vlan_filtering && ds->vlan_filtering_is_global) {
+		dsa_switch_for_each_port(dp, ds) {
+			struct net_device *br = dsa_port_bridge_dev_get(dp);
+
+			if (br && br_vlan_enabled(br)) {
+				change_vlan_filtering = false;
+				break;
+			}
+		}
+	}
+
+	if (!change_vlan_filtering)
+		return;
+
+	err = dsa_port_vlan_filtering(dp, vlan_filtering, &extack);
+	if (extack._msg) {
+		dev_err(ds->dev, "port %d: %s\n", dp->index,
+			extack._msg);
+	}
+	if (err && err != -EOPNOTSUPP) {
+		dev_err(ds->dev,
+			"port %d failed to reset VLAN filtering to %d: %pe\n",
+		       dp->index, vlan_filtering, ERR_PTR(err));
+	}
+}
+
 static int dsa_port_inherit_brport_flags(struct dsa_port *dp,
 					 struct netlink_ext_ack *extack)
 {
@@ -243,7 +296,8 @@ static int dsa_port_switchdev_sync_attrs(struct dsa_port *dp,
 	return 0;
 }
 
-static void dsa_port_switchdev_unsync_attrs(struct dsa_port *dp)
+static void dsa_port_switchdev_unsync_attrs(struct dsa_port *dp,
+					    struct dsa_bridge bridge)
 {
 	/* Configure the port for standalone mode (no address learning,
 	 * flood everything).
@@ -263,7 +317,7 @@ static void dsa_port_switchdev_unsync_attrs(struct dsa_port *dp)
 	 */
 	dsa_port_set_state_now(dp, BR_STATE_FORWARDING, true);
 
-	/* VLAN filtering is handled by dsa_switch_bridge_leave */
+	dsa_port_reset_vlan_filtering(dp, bridge);
 
 	/* Ageing time may be global to the switch chip, so don't change it
 	 * here because we have no good reason (or value) to change it to.
@@ -418,7 +472,7 @@ void dsa_port_bridge_leave(struct dsa_port *dp, struct net_device *br)
 			"port %d failed to notify DSA_NOTIFIER_BRIDGE_LEAVE: %pe\n",
 			dp->index, ERR_PTR(err));
 
-	dsa_port_switchdev_unsync_attrs(dp);
+	dsa_port_switchdev_unsync_attrs(dp, info.bridge);
 }
 
 int dsa_port_lag_change(struct dsa_port *dp,
diff --git a/net/dsa/switch.c b/net/dsa/switch.c
index d25cd1da3eb3..d8a80cf9742c 100644
--- a/net/dsa/switch.c
+++ b/net/dsa/switch.c
@@ -115,62 +115,10 @@ static int dsa_switch_bridge_join(struct dsa_switch *ds,
 	return 0;
 }
 
-static int dsa_switch_sync_vlan_filtering(struct dsa_switch *ds,
-					  struct dsa_notifier_bridge_info *info)
-{
-	struct netlink_ext_ack extack = {0};
-	bool change_vlan_filtering = false;
-	bool vlan_filtering;
-	struct dsa_port *dp;
-	int err;
-
-	if (ds->needs_standalone_vlan_filtering &&
-	    !br_vlan_enabled(info->bridge.dev)) {
-		change_vlan_filtering = true;
-		vlan_filtering = true;
-	} else if (!ds->needs_standalone_vlan_filtering &&
-		   br_vlan_enabled(info->bridge.dev)) {
-		change_vlan_filtering = true;
-		vlan_filtering = false;
-	}
-
-	/* If the bridge was vlan_filtering, the bridge core doesn't trigger an
-	 * event for changing vlan_filtering setting upon slave ports leaving
-	 * it. That is a good thing, because that lets us handle it and also
-	 * handle the case where the switch's vlan_filtering setting is global
-	 * (not per port). When that happens, the correct moment to trigger the
-	 * vlan_filtering callback is only when the last port leaves the last
-	 * VLAN-aware bridge.
-	 */
-	if (change_vlan_filtering && ds->vlan_filtering_is_global) {
-		dsa_switch_for_each_port(dp, ds) {
-			struct net_device *br = dsa_port_bridge_dev_get(dp);
-
-			if (br && br_vlan_enabled(br)) {
-				change_vlan_filtering = false;
-				break;
-			}
-		}
-	}
-
-	if (change_vlan_filtering) {
-		err = dsa_port_vlan_filtering(dsa_to_port(ds, info->port),
-					      vlan_filtering, &extack);
-		if (extack._msg)
-			dev_err(ds->dev, "port %d: %s\n", info->port,
-				extack._msg);
-		if (err && err != -EOPNOTSUPP)
-			return err;
-	}
-
-	return 0;
-}
-
 static int dsa_switch_bridge_leave(struct dsa_switch *ds,
 				   struct dsa_notifier_bridge_info *info)
 {
 	struct dsa_switch_tree *dst = ds->dst;
-	int err;
 
 	if (dst->index == info->tree_index && ds->index == info->sw_index &&
 	    ds->ops->port_bridge_leave)
@@ -182,12 +130,6 @@ static int dsa_switch_bridge_leave(struct dsa_switch *ds,
 						info->sw_index, info->port,
 						info->bridge);
 
-	if (ds->dst->index == info->tree_index && ds->index == info->sw_index) {
-		err = dsa_switch_sync_vlan_filtering(ds, info);
-		if (err)
-			return err;
-	}
-
 	return 0;
 }
 
-- 
2.25.1