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

[wanghai (M)]

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 ->
> > > > 			device_add(dev)
> > > > 			register_queue_kobjects(ndev)
> > > >
> > > > 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)->kobj.name 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...
> > > > backtrace:
> > > >     [<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);
> > > >    
> > > > +out:
> > > >    	return error;
> > > > +
> > > > +register_error:
> > > > +	device_del(dev);
> > > > +device_add_error:
> > > > +	kfree_const(dev->kobj.name);
> > > This looks a bug in device_add() not here.
> > > In general, it is better for an api to clean up after itself.
> > > Since dev->kobj.name 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->kobj.name 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-> kobj.name
> > 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->kobj.name. 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()