Subject: Re: [PATCH net] net: fix memory leak in register_netdevice() on error path

From: Stephen Hemminger <[email-masked]>
Date: Sun, 29 Nov 2020 20:39:33 -0800

On Thu, 26 Nov 2020 21:23:12 +0800
Yang Yingliang <[email-masked]> wrote:

> I got a memleak report when doing fault-inject test:
> 
> unreferenced object 0xffff88810ace9000 (size 1024):
>   comm "ip", pid 4622, jiffies 4295457037 (age 43.378s)
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<00000000008abe41>] __kmalloc+0x10f/0x210
>     [<000000005d3533a6>] veth_dev_init+0x140/0x310
>     [<0000000088353c64>] register_netdevice+0x496/0x7a0
>     [<000000001324d322>] veth_newlink+0x40b/0x960
>     [<00000000d0799866>] __rtnl_newlink+0xd8c/0x1360
>     [<00000000d616040a>] rtnl_newlink+0x6b/0xa0
>     [<00000000e0a1600d>] rtnetlink_rcv_msg+0x3cc/0x9e0
>     [<000000009eeff98b>] netlink_rcv_skb+0x130/0x3a0
>     [<00000000500f8be1>] netlink_unicast+0x4da/0x700
>     [<00000000666c03b3>] netlink_sendmsg+0x7fe/0xcb0
>     [<0000000073b28103>] sock_sendmsg+0x143/0x180
>     [<00000000ad746a30>] ____sys_sendmsg+0x677/0x810
>     [<0000000087dd98e5>] ___sys_sendmsg+0x105/0x180
>     [<00000000028dd365>] __sys_sendmsg+0xf0/0x1c0
>     [<00000000a6bfbae6>] do_syscall_64+0x33/0x40
>     [<00000000e00521b4>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> It seems ifb and loopback may also hit the leak, so I try to fix this in
> register_netdevice().
> 
> In common case, priv_destructor() will be called in netdev_run_todo()
> after calling ndo_uninit() in rollback_registered(), on other error
> path in register_netdevice(), ndo_uninit() and priv_destructor() are
> called before register_netdevice() return, but in this case,
> priv_destructor() will never be called, then it causes memory leak,
> so we should call priv_destructor() here.
> 
> Reported-by: Hulk Robot <[email-masked]>
> Signed-off-by: Yang Yingliang <[email-masked]>
> ---
>  net/core/dev.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 82dc6b48e45f..907204395b64 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10000,6 +10000,17 @@ int register_netdevice(struct net_device *dev)
>  	ret = notifier_to_errno(ret);
>  	if (ret) {
>  		rollback_registered(dev);
> +		/*
> +		 * In common case, priv_destructor() will be
> +		 * called in netdev_run_todo() after calling
> +		 * ndo_uninit() in rollback_registered().
> +		 * But in this case, priv_destructor() will
> +		 * never be called, then it causes memory
> +		 * leak, so we should call priv_destructor()
> +		 * here.
> +		 */
> +		if (dev->priv_destructor)
> +			dev->priv_destructor(dev);

Are you sure this is safe?
Several devices have destructors that call free_netdev.
Up until now a common pattern for those devices was to call
free_netdev on error. After this change it would lead to double free.