netdev - Re: [PATCH] tg3: Avoid NULL pointer dereference in tg3_get

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Date:   Thu, 5 Jan 2017 12:04:13 -0800
From:   Michael Chan <michael.chan@...adcom.com>
To:     David Miller <davem@...emloft.net>
Cc:     wangyufen@...wei.com, Siva Reddy Kallam <siva.kallam@...adcom.com>,
        "prashant.sreedharan@...adcom.com" <prashant@...adcom.com>,
        "michael.chan@...adcom.com" <mchan@...adcom.com>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] tg3: Avoid NULL pointer dereference in tg3_get_nstats()

On Thu, Jan 5, 2017 at 9:33 AM, David Miller <davem@...emloft.net> wrote:
> From: Wang Yufen <wangyufen@...wei.com>
> Date: Thu, 5 Jan 2017 22:13:21 +0800
>
>> From: Yufen Wang <wangyufen@...wei.com>
>>
>> A possible NULL pointer dereference in tg3_get_stats64 while doing
>> tg3_free_consistent.
>  ...
>> This patch avoids the NULL pointer dereference by using !tg3_flag(tp, INIT_COMPLETE)
>> instate of !tp->hw_stats.
>>
>> Signed-off-by: Yufen Wang <wangyufen@...wei.com>
>> ---
>>  drivers/net/ethernet/broadcom/tg3.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
>> index 185e9e0..012f18d 100644
>> --- a/drivers/net/ethernet/broadcom/tg3.c
>> +++ b/drivers/net/ethernet/broadcom/tg3.c
>> @@ -14148,7 +14148,7 @@ static struct rtnl_link_stats64 *tg3_get_stats64(struct net_device *dev,
>>       struct tg3 *tp = netdev_priv(dev);
>>
>>       spin_lock_bh(&tp->lock);
>> -     if (!tp->hw_stats) {
>> +     if (!tg3_flag(tp, INIT_COMPLETE)) {
>
> The real issue is the manner and order in which the driver performs
> initialization actions relative to netif_device_{attach,detach}().
>
> That is what needs to be fixed here, instead of adding more and more
> ad-hoc tests to the various methods which can be invoked once the
> netif_device_attach() occurs.

Normally, ndo_get_stats64() should be under rtnl lock in the netlink
code path and we should be safe. We only free tp->hw_stats under rtnl
lock in the close path or ethtool path.

But it looks like ndo_get_stats() can be called without rtnl lock from
net-procfs.c.  So it is possible that we'll read tp->hw_stats after it
has been freed.  For example, if we are reading /proc/net/dev and
closing tg3 at the same time.  David, is not taking rtnl_lock in
net-procfs.c by design?