netdev - Re: [PATCH net] net: fix memory leak in register

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Date:   Mon, 30 Nov 2020 19:12:08 +0800
From:   Yang Yingliang <yangyingliang@...wei.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
CC:     <netdev@...r.kernel.org>, <davem@...emloft.net>, <kuba@...nel.org>,
        <toshiaki.makita1@...il.com>, <rkovhaev@...il.com>
Subject: Re: [PATCH net] net: fix memory leak in register_netdevice() on error
 path


On 2020/11/30 12:39, Stephen Hemminger wrote:
> On Thu, 26 Nov 2020 21:23:12 +0800
> Yang Yingliang <yangyingliang@...wei.com> 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>
>> ---
>>   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.

After commit cf124db566e6 ("net: Fix inconsistent teardown and release 
of private netdev state."),

free_netdev() is not be called in priv_destructor().

>
> .