[PATCH net-next 0/2] netconsole: add locking to configfs _show callbacks

[PATCH net-next 0/2] netconsole: add locking to configfs _show callbacks

[Gustavo Luiz Duarte]

Patch 1 fixes a couple of reports from sashiko by adding proper locking
to configs read callbacks to avoid printing partially updated data.
Patch 2 is mostly cosmetic but worth fixing.

Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
---
Gustavo Luiz Duarte (2):
      netconsole: avoid printing partially updated target attributes
      netconsole: remove unnecessary target refcounting from the netdev notifier

 drivers/net/netconsole.c | 93 ++++++++++++++++++++++++++----------------------
 1 file changed, 51 insertions(+), 42 deletions(-)
---
base-commit: 8b4e7209c842d8cb9516f1f5ef0a88aa2d8831a6
change-id: 20261005-netcons-fixes-next-af0db028f570

Best regards,
--  
Gustavo Luiz Duarte <gustavold@gmail.com>

[PATCH net-next 1/2] netconsole: avoid printing partially updated target attributes

[Gustavo Luiz Duarte]

The configfs store callbacks all serialize on dynamic_netconsole_mutex
but not on the read side, so reading an attribute while it is being
written returns a partially updated value.

Hold dynamic_netconsole_mutex on *_show() callbacks to avoid racing with
writers.

The dev_name_show() callback can also race with
netconsole_netdev_event() writing to np.dev_name due to
NETDEV_CHANGENAME. So it needs to hold RTNL in addition to
dynamic_netconsole_mutex.

Reported-by: Sashiko <netdev-bot+sashiko@kernel.org>
Closes: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260814-netcons_ipv6-v3-7-bc0915e8c75f@gmail.com
Closes: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260928-netcons-fixes-v1-0-bb5ffe5e698a%40gmail.com
Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
---
 drivers/net/netconsole.c | 62 +++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 51 insertions(+), 11 deletions(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 267254f046de..188beacb308d 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -859,7 +859,19 @@ static ssize_t release_show(struct config_item *item, char *buf)
 
 static ssize_t dev_name_show(struct config_item *item, char *buf)
 {
-	return sysfs_emit(buf, "%s\n", to_target(item)->np.dev_name);
+	struct netconsole_target *nt = to_target(item);
+	int ret;
+
+	dynamic_netconsole_mutex_lock();
+	/* Hold RTNL to prevent racing against netconsole_netdev_event()
+	 * changing np.dev_name.
+	 */
+	rtnl_lock();
+	ret = sysfs_emit(buf, "%s\n", nt->np.dev_name);
+	rtnl_unlock();
+	dynamic_netconsole_mutex_unlock();
+
+	return ret;
 }
 
 static ssize_t local_port_show(struct config_item *item, char *buf)
@@ -875,25 +887,39 @@ static ssize_t remote_port_show(struct config_item *item, char *buf)
 static ssize_t local_ip_show(struct config_item *item, char *buf)
 {
 	struct netconsole_target *nt = to_target(item);
+	int ret;
+
+	dynamic_netconsole_mutex_lock();
 
 	if (nt->local_ip.family == AF_UNSPEC)
-		return sysfs_emit(buf, "\n");
-	if (nt->local_ip.family == AF_INET6)
-		return sysfs_emit(buf, "%pI6c\n", &nt->local_ip.in6);
+		ret = sysfs_emit(buf, "\n");
+	else if (nt->local_ip.family == AF_INET6)
+		ret = sysfs_emit(buf, "%pI6c\n", &nt->local_ip.in6);
 	else
-		return sysfs_emit(buf, "%pI4\n", &nt->local_ip.ip);
+		ret = sysfs_emit(buf, "%pI4\n", &nt->local_ip.ip);
+
+	dynamic_netconsole_mutex_unlock();
+
+	return ret;
 }
 
 static ssize_t remote_ip_show(struct config_item *item, char *buf)
 {
 	struct netconsole_target *nt = to_target(item);
+	int ret;
+
+	dynamic_netconsole_mutex_lock();
 
 	if (nt->remote_ip.family == AF_UNSPEC)
-		return sysfs_emit(buf, "\n");
-	if (nt->remote_ip.family == AF_INET6)
-		return sysfs_emit(buf, "%pI6c\n", &nt->remote_ip.in6);
+		ret = sysfs_emit(buf, "\n");
+	else if (nt->remote_ip.family == AF_INET6)
+		ret = sysfs_emit(buf, "%pI6c\n", &nt->remote_ip.in6);
 	else
-		return sysfs_emit(buf, "%pI4\n", &nt->remote_ip.ip);
+		ret = sysfs_emit(buf, "%pI4\n", &nt->remote_ip.ip);
+
+	dynamic_netconsole_mutex_unlock();
+
+	return ret;
 }
 
 static ssize_t local_mac_show(struct config_item *item, char *buf)
@@ -906,7 +932,14 @@ static ssize_t local_mac_show(struct config_item *item, char *buf)
 
 static ssize_t remote_mac_show(struct config_item *item, char *buf)
 {
-	return sysfs_emit(buf, "%pM\n", to_target(item)->remote_mac);
+	struct netconsole_target *nt = to_target(item);
+	int ret;
+
+	dynamic_netconsole_mutex_lock();
+	ret = sysfs_emit(buf, "%pM\n", nt->remote_mac);
+	dynamic_netconsole_mutex_unlock();
+
+	return ret;
 }
 
 static ssize_t transmit_errors_show(struct config_item *item, char *buf)
@@ -1342,7 +1375,14 @@ static struct netconsole_target *userdata_to_target(struct userdata *ud)
 
 static ssize_t userdatum_value_show(struct config_item *item, char *buf)
 {
-	return sysfs_emit(buf, "%s\n", &(to_userdatum(item)->value[0]));
+	struct userdatum *udm = to_userdatum(item);
+	int ret;
+
+	dynamic_netconsole_mutex_lock();
+	ret = sysfs_emit(buf, "%s\n", udm->value);
+	dynamic_netconsole_mutex_unlock();
+
+	return ret;
 }
 
 /* Navigate configfs and calculate the lentgh of the formatted string

-- 
2.55.0

Re: [PATCH net-next 1/2] netconsole: avoid printing partially updated target attributes

[Eric Dumazet]

On 10/6/26 20:58, Gustavo Luiz Duarte wrote:
> The configfs store callbacks all serialize on dynamic_netconsole_mutex
> but not on the read side, so reading an attribute while it is being
> written returns a partially updated value.
> 
> Hold dynamic_netconsole_mutex on *_show() callbacks to avoid racing with
> writers.
> 
> The dev_name_show() callback can also race with
> netconsole_netdev_event() writing to np.dev_name due to
> NETDEV_CHANGENAME. So it needs to hold RTNL in addition to
> dynamic_netconsole_mutex.
> 
> Reported-by: Sashiko <netdev-bot+sashiko@kernel.org>
> Closes: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260814-netcons_ipv6-v3-7-bc0915e8c75f@gmail.com
> Closes: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260928-netcons-fixes-v1-0-bb5ffe5e698a%40gmail.com
> Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
> ---
>   drivers/net/netconsole.c | 62 +++++++++++++++++++++++++++++++++++++++---------
>   1 file changed, 51 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index 267254f046de..188beacb308d 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -859,7 +859,19 @@ static ssize_t release_show(struct config_item *item, char *buf)
>   
>   static ssize_t dev_name_show(struct config_item *item, char *buf)
>   {
> -	return sysfs_emit(buf, "%s\n", to_target(item)->np.dev_name);
> +	struct netconsole_target *nt = to_target(item);
> +	int ret;
> +
> +	dynamic_netconsole_mutex_lock();
> +	/* Hold RTNL to prevent racing against netconsole_netdev_event()
> +	 * changing np.dev_name.
> +	 */
> +	rtnl_lock();
> +	ret = sysfs_emit(buf, "%s\n", nt->np.dev_name);
> +	rtnl_unlock();
> +	dynamic_netconsole_mutex_unlock();
> +
> +	return ret;
>   }

Please do not add rtnl_lock() in a _show() sysfs handler unless there is 
no other way?

Something like:

     dynamic_netconsole_mutex_lock();
     strscpy(name, nt->np.dev_name, sizeof(name));
     if (nt->state == STATE_ENABLED) {
         struct net_device *dev = nt->np.dev;

         if (dev)
             netdev_copy_name(dev, name);
     }
     dynamic_netconsole_mutex_unlock();

[PATCH net-next 2/2] netconsole: remove unnecessary target refcounting from the netdev notifier

[Gustavo Luiz Duarte]

Since netconsole_netdev_event() holds target_list_lock, there is no need
to also protect each target with netconsole_target_get/put()
refcounting. There is no way a target reachable from the target_list
would go away while we hold target_list_lock.

This is similar to commit a6d403ac9689 ("netconsole: remove unnecessary
netconsole_target_get/out() from write_msg()").

Since this is the only remaining user of netconsole_target_get/put(),
remove those helpers as well.

Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
---
 drivers/net/netconsole.c | 31 -------------------------------
 1 file changed, 31 deletions(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 188beacb308d..ddc5fcf19fe6 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -262,23 +262,6 @@ static void __exit dynamic_netconsole_exit(void)
 	configfs_unregister_subsystem(&netconsole_subsys);
 }
 
-/*
- * Targets that were created by parsing the boot/module option string
- * do not exist in the configfs hierarchy (and have NULL names) and will
- * never go away, so make these a no-op for them.
- */
-static void netconsole_target_get(struct netconsole_target *nt)
-{
-	if (config_item_name(&nt->group.cg_item))
-		config_group_get(&nt->group);
-}
-
-static void netconsole_target_put(struct netconsole_target *nt)
-{
-	if (config_item_name(&nt->group.cg_item))
-		config_group_put(&nt->group);
-}
-
 static void dynamic_netconsole_mutex_lock(void)
 {
 	mutex_lock(&dynamic_netconsole_mutex);
@@ -300,18 +283,6 @@ static void __exit dynamic_netconsole_exit(void)
 {
 }
 
-/*
- * No danger of targets going away from under us when dynamic
- * reconfigurability is off.
- */
-static void netconsole_target_get(struct netconsole_target *nt)
-{
-}
-
-static void netconsole_target_put(struct netconsole_target *nt)
-{
-}
-
 static void populate_configfs_item(struct netconsole_target *nt,
 				   int cmdline_count)
 {
@@ -1979,7 +1950,6 @@ static int netconsole_netdev_event(struct notifier_block *this,
 	mutex_lock(&target_cleanup_list_lock);
 	spin_lock_irqsave(&target_list_lock, flags);
 	list_for_each_entry_safe(nt, tmp, &target_list, list) {
-		netconsole_target_get(nt);
 		if (nt->np.dev == dev) {
 			switch (event) {
 			case NETDEV_CHANGENAME:
@@ -2009,7 +1979,6 @@ static int netconsole_netdev_event(struct notifier_block *this,
 			 * notifier.
 			 */
 			queue_work(netconsole_wq, &nt->resume_wq);
-		netconsole_target_put(nt);
 	}
 	spin_unlock_irqrestore(&target_list_lock, flags);
 	mutex_unlock(&target_cleanup_list_lock);

-- 
2.55.0

Re: [PATCH net-next 0/2] netconsole: add locking to configfs _show callbacks

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - Whether the issue was actually triggered, or is only theoretical
   (e.g. found by code inspection). If it was triggered please include
   the symptoms, like the stack trace or error messages.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.