Once device_add() failed, we should call put_device() to decrement
reference count for cleanup. Or it could cause memory leak.

As comment of device_add() says, 'if device_add() succeeds, you should
call device_del() when you want to get rid of it. If device_add() has
not succeeded, use only put_device() to drop the reference count'.

Found by code review.

Cc: stable@vger.kernel.org
Fixes: 8ed633b9baf9 ("Revert "net-sysfs: Fix memory leak in netdev_register_kobject"")
Signed-off-by: Ma Ke <make24@iscas.ac.cn>
---
 net/core/net-sysfs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 07cb99b114bd..f443eacc9237 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -2169,6 +2169,7 @@ int netdev_register_kobject(struct net_device *ndev)
 
 	error = device_add(dev);
 	if (error)
+		put_device(dev);
 		return error;
 
 	error = register_queue_kobjects(ndev);
-- 
2.25.1

On Thu, Mar 13, 2025 at 03:55:28PM +0800, Ma Ke wrote:
> Once device_add() failed, we should call put_device() to decrement
> reference count for cleanup. Or it could cause memory leak.
> 
> As comment of device_add() says, 'if device_add() succeeds, you should
> call device_del() when you want to get rid of it. If device_add() has
> not succeeded, use only put_device() to drop the reference count'.
> 
> Found by code review.
> 
> Cc: stable@vger.kernel.org
> Fixes: 8ed633b9baf9 ("Revert "net-sysfs: Fix memory leak in netdev_register_kobject"")
> Signed-off-by: Ma Ke <make24@iscas.ac.cn>
> ---
>  net/core/net-sysfs.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 07cb99b114bd..f443eacc9237 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -2169,6 +2169,7 @@ int netdev_register_kobject(struct net_device *ndev)
>  
>  	error = device_add(dev);
>  	if (error)
> +		put_device(dev);
>  		return error;

You obviously did not test this :(

Please be more careful in the future.

On Thu, Mar 13, 2025 at 03:55:28PM +0800, Ma Ke wrote:
> Once device_add() failed, we should call put_device() to decrement
> reference count for cleanup. Or it could cause memory leak.
> 
> As comment of device_add() says, 'if device_add() succeeds, you should
> call device_del() when you want to get rid of it. If device_add() has
> not succeeded, use only put_device() to drop the reference count'.

Okay, have you read the history of this?
6b70fc94afd1 ("net-sysfs: Fix memory leak in netdev_register_kobject")
8ed633b9baf9 ("Revert "net-sysfs: Fix memory leak in netdev_register_kobject"")
https://syzkaller.appspot.com/x/log.txt?x=1737671b200000

TL;DR: next time provide a better changelog and clean syzkaller report.

-- 
With Best Regards,
Andy Shevchenko

+Cc: Wang Hai

On Thu, Mar 13, 2025 at 11:01:18AM +0200, Andy Shevchenko wrote:
> On Thu, Mar 13, 2025 at 03:55:28PM +0800, Ma Ke wrote:
> > Once device_add() failed, we should call put_device() to decrement
> > reference count for cleanup. Or it could cause memory leak.
> > 
> > As comment of device_add() says, 'if device_add() succeeds, you should
> > call device_del() when you want to get rid of it. If device_add() has
> > not succeeded, use only put_device() to drop the reference count'.
> 
> Okay, have you read the history of this?
> 6b70fc94afd1 ("net-sysfs: Fix memory leak in netdev_register_kobject")
> 8ed633b9baf9 ("Revert "net-sysfs: Fix memory leak in netdev_register_kobject"")
> https://syzkaller.appspot.com/x/log.txt?x=1737671b200000
> 
> TL;DR: next time provide a better changelog and clean syzkaller report.

-- 
With Best Regards,
Andy Shevchenko