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Date:   Wed, 2 Dec 2020 16:37:51 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <toshiaki.makita1@...il.com>, <rkovhaev@...il.com>,
        <stephen@...workplumber.org>, <Jason@...c4.com>
Subject: Re: [PATCH net v3] net: fix memory leak in register_netdevice() on
 error path

On Tue, 1 Dec 2020 21:54:57 +0800 Yang Yingliang 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 <hulkci@...wei.com>
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
> v2 -> v3: In wireguard driver, priv_destructor() will call
> free_netdev(), but it is assigned after register_netdevice(),
> so it will not lead a double free, drop patch#1. Also I've
> test wireguard device, it's no memory leak on this error path.

Sorry I don't want to apply yet another wobbly workaround to this path.
I started hacking on a rework of the registration / free which will
solve this and all the other corner cases which are broken around here.
Stay tuned.

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