Subject: Re: [PATCH] net-sysfs: Fix memory leak in register_queue_kobjects

From: [email-masked] (Jouni Högander)
Date: Tue, 19 Nov 2019 11:23:18 +0200

[email-masked] writes:

> From: Jouni Hogander <[email-masked]>
>
> net_rx_queue_update_kobjects and netdev_queue_update_kobjects are
> leaking memory in their error paths. Leak was originally reported
> by Syzkaller:
>
> BUG: memory leak
> unreferenced object 0xffff8880679f8b08 (size 8):
>   comm "netdev_register", pid 269, jiffies 4294693094 (age 12.132s)
>   hex dump (first 8 bytes):
>     72 78 2d 30 00 36 20 d4                          rx-0.6 .
>   backtrace:
>     [<000000008c93818e>] __kmalloc_track_caller+0x16e/0x290
>     [<000000001f2e4e49>] kvasprintf+0xb1/0x140
>     [<000000007f313394>] kvasprintf_const+0x56/0x160
>     [<00000000aeca11c8>] kobject_set_name_vargs+0x5b/0x140
>     [<0000000073a0367c>] kobject_init_and_add+0xd8/0x170
>     [<0000000088838e4b>] net_rx_queue_update_kobjects+0x152/0x560
>     [<000000006be5f104>] netdev_register_kobject+0x210/0x380
>     [<00000000e31dab9d>] register_netdevice+0xa1b/0xf00
>     [<00000000f68b2465>] __tun_chr_ioctl+0x20d5/0x3dd0
>     [<000000004c50599f>] tun_chr_ioctl+0x2f/0x40
>     [<00000000bbd4c317>] do_vfs_ioctl+0x1c7/0x1510
>     [<00000000d4c59e8f>] ksys_ioctl+0x99/0xb0
>     [<00000000946aea81>] __x64_sys_ioctl+0x78/0xb0
>     [<0000000038d946e5>] do_syscall_64+0x16f/0x580
>     [<00000000e0aa5d8f>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>     [<00000000285b3d1a>] 0xffffffffffffffff
>
> Cc: David Miller <[email-masked]>
> Cc: Lukas Bulwahn <[email-masked]>
> Signed-off-by: Jouni Hogander <[email-masked]>
> ---
>  net/core/net-sysfs.c | 34 ++++++++++++++++++++++++----------
>  1 file changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 865ba6ca16eb..2f44c6a3bcae 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -923,20 +923,25 @@ static int rx_queue_add_kobject(struct net_device *dev, int index)
>  	error = kobject_init_and_add(kobj, &rx_queue_ktype, NULL,
>  				     "rx-%u", index);
>  	if (error)
> -		return error;
> +		goto err_init_and_add;
>  
>  	dev_hold(queue->dev);
>  
>  	if (dev->sysfs_rx_queue_group) {
>  		error = sysfs_create_group(kobj, dev->sysfs_rx_queue_group);
> -		if (error) {
> -			kobject_put(kobj);
> -			return error;
> -		}
> +		if (error)
> +			goto err_sysfs_create;
>  	}
>  
>  	kobject_uevent(kobj, KOBJ_ADD);
>  
> +	return error;
> +
> +err_sysfs_create:
> +	kobject_put(kobj);
> +err_init_and_add:
> +	kfree_const(kobj->name);
> +
>  	return error;
>  }
>  #endif /* CONFIG_SYSFS */
> @@ -968,6 +973,7 @@ net_rx_queue_update_kobjects(struct net_device *dev, int old_num, int new_num)
>  		if (dev->sysfs_rx_queue_group)
>  			sysfs_remove_group(kobj, dev->sysfs_rx_queue_group);
>  		kobject_put(kobj);
> +		kfree_const(kobj->name);
>  	}
>  
>  	return error;
> @@ -1461,21 +1467,28 @@ static int netdev_queue_add_kobject(struct net_device *dev, int index)
>  	error = kobject_init_and_add(kobj, &netdev_queue_ktype, NULL,
>  				     "tx-%u", index);
>  	if (error)
> -		return error;
> +		goto err_init_and_add;
>  
>  	dev_hold(queue->dev);
>  
>  #ifdef CONFIG_BQL
>  	error = sysfs_create_group(kobj, &dql_group);
> -	if (error) {
> -		kobject_put(kobj);
> -		return error;
> -	}
> +	if (error)
> +		goto err_sysfs_create;
>  #endif
>  
>  	kobject_uevent(kobj, KOBJ_ADD);
>  
>  	return 0;
> +
> +#ifdef CONFIG_BQL
> +err_sysfs_create:
> +	kobject_put(kobj);
> +#endif
> +err_init_and_add:
> +	kfree_const(kobj->name);
> +
> +	return error;
>  }
>  #endif /* CONFIG_SYSFS */
>  
> @@ -1503,6 +1516,7 @@ netdev_queue_update_kobjects(struct net_device *dev, int old_num, int new_num)
>  		sysfs_remove_group(&queue->kobj, &dql_group);
>  #endif
>  		kobject_put(&queue->kobj);
> +		kfree_const(queue->kobj.name);
>  	}
>  
>  	return error;

This patch should be ignored. Rootcause for this memory leak is
reference count leak. I will upload another patch.

BR,

Jouni Högander