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

From: wanghai (M)
Date: Mon Mar 18 2019 - 23:40:40 EST

å 2019/3/19 11:15, Stephen Hemminger åé:
On Tue, 19 Mar 2019 11:03:54 +0800
"wanghai (M)" <wanghai26@xxxxxxxxxx> wrote:

å 2019/3/18 23:57, Stephen Hemminger åé:
On Tue, 19 Mar 2019 01:06:57 -0400
Wang Hai <wanghai26@xxxxxxxxxx> wrote:
When registering struct net_device, it will call
register_netdevice ->
netdev_register_kobject ->

If device_add(dev) or register_queue_kobjects(ndev) fails.
Register_netdevice() will return error, causing netdev_freemem(ndev)
to be called to free net_device, however (&ndev->dev)-> will
not be freed, resulting in a memory leak.

syzkaller report this:
BUG: memory leak
unreferenced object 0xffff8881f4fad168 (size 8):
comm "syz-executor.0", pid 3575, jiffies 4294778002 (age 20.134s)
hex dump (first 8 bytes):
77 70 61 6e 30 00 ff ff wpan0...
[<000000006d2d91d7>] kstrdup_const+0x3d/0x50 mm/util.c:73
[<00000000ba9ff953>] kvasprintf_const+0x112/0x170 lib/kasprintf.c:48
[<000000005555ec09>] kobject_set_name_vargs+0x55/0x130 lib/kobject.c:281
[<0000000098d28ec3>] dev_set_name+0xbb/0xf0 drivers/base/core.c:1915
[<00000000b7553017>] netdev_register_kobject+0xc0/0x410 net/core/net-sysfs.c:1727
[<00000000c826a797>] register_netdevice+0xa51/0xeb0 net/core/dev.c:8711
[<00000000857bfcfd>] cfg802154_update_iface_num.isra.2+0x13/0x90 [ieee802154]
[<000000003126e453>] ieee802154_llsec_fill_key_id+0x1d5/0x570 [ieee802154]
[<00000000e4b3df51>] 0xffffffffc1500e0e
[<00000000b4319776>] platform_drv_probe+0xc6/0x180 drivers/base/platform.c:614
[<0000000037669347>] really_probe+0x491/0x7c0 drivers/base/dd.c:509
[<000000008fed8862>] driver_probe_device+0xdc/0x240 drivers/base/dd.c:671
[<00000000baf52041>] device_driver_attach+0xf2/0x130 drivers/base/dd.c:945
[<00000000c7cc8dec>] __driver_attach+0x10e/0x210 drivers/base/dd.c:1022
[<0000000057a757c2>] bus_for_each_dev+0x154/0x1e0 drivers/base/bus.c:304
[<000000005f5ae04b>] bus_add_driver+0x427/0x5e0 drivers/base/bus.c:645

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Fixes: 1d24eb4815d1 ("xps: Transmit Packet Steering")
Signed-off-by: Wang Hai <wanghai26@xxxxxxxxxx>
net/core/net-sysfs.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 4ff661f..f0e53dc 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1745,17 +1745,22 @@ int netdev_register_kobject(struct net_device *ndev)
error = device_add(dev);
if (error)
- return error;
+ goto device_add_error;
error = register_queue_kobjects(ndev);
- if (error) {
- device_del(dev);
- return error;
- }
+ if (error)
+ goto register_error;
pm_runtime_set_memalloc_noio(dev, true);
return error;
+ device_del(dev);
+ kfree_const(dev->;
This looks a bug in device_add() not here.
In general, it is better for an api to clean up after itself.
Since dev-> is created in device_add and normally freed
in device_del; why is device_add leaving it behind?\
When registering struct net_device, it will call
register_netdevice ->
ÂÂÂ netdev_register_kobject ->
ÂÂÂ ÂÂÂ dev_set_name(dev, "%s", ndev->name)
ÂÂÂÂ ÂÂÂ device_add(dev)
ÂÂÂÂ ÂÂÂ register_queue_kobjects(ndev)

The dev-> that causes the memory leak is created in
dev_set_name(dev, "%s", ndev-> name) in the function
netdev_register_kobject(), not in device_add(dev). If device_add(dev) or
register_queue_kobjects(ndev) fails, it should release dev->
in netdev_register_kobject()
Good catch, dev_set_name is using asprintf to allocate new memory
for the name. The problem with your patch is that device_del()
already cleans up the device (including name). The device object
should really not be touched after device_del.

Where is the name freed in the normal case?

Device_del just delete device from system, but do not clean up dev-> In normal case, the name is freed in free_netdev(dev)->put_device(&dev->dev)->kobject_put(&dev->kobj)->kobject_cleanup() ,not in device_del()