netdev - Re: [PATCH net v2] ipv6: Handle race in addrconf_dad

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Date:   Wed, 2 Oct 2019 14:23:04 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Ahern <dsahern@...nel.org>, davem@...emloft.net,
        jakub.kicinski@...ronome.com
Cc:     netdev@...r.kernel.org, rajendra.dendukuri@...adcom.com,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH net v2] ipv6: Handle race in addrconf_dad_work



On 10/2/19 2:08 PM, Eric Dumazet wrote:
> 
> 
> On 10/1/19 11:18 AM, Eric Dumazet wrote:
>>
>>
>> On 9/30/19 8:28 PM, David Ahern wrote:
>>> From: David Ahern <dsahern@...il.com>
>>>
>>> Rajendra reported a kernel panic when a link was taken down:
>>>
>>> [ 6870.263084] BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8
>>> [ 6870.271856] IP: [<ffffffff8efc5764>] __ipv6_ifa_notify+0x154/0x290
>>>
>>> <snip>
>>>
>>
>> Reviewed-by: Eric Dumazet <edumazet@...gle.com>
>>
>> Thanks !
>>
> 
> Apparently this patch causes problems. I yet have to make an analysis.
> 

It seems we need to allow the code to do some changes if IF_READY is not set.

WDYT ?

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index dd3be06d5a066e494617d4917c757eae19340d4d..e8181a3700213b9574ea25130689c9218236245d 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4035,7 +4035,7 @@ static void addrconf_dad_work(struct work_struct *w)
        /* check if device was taken down before this delayed work
         * function could be canceled
         */
-       if (idev->dead || !(idev->if_flags & IF_READY))
+       if (idev->dead)
                goto out;
 
        spin_lock_bh(&ifp->lock);
@@ -4083,6 +4083,11 @@ static void addrconf_dad_work(struct work_struct *w)
                goto out;
 
        write_lock_bh(&idev->lock);
+       if (!(idev->if_flags & IF_READY)) {
+               write_unlock_bh(&idev->lock);
+               goto out;
+       }
+
        spin_lock(&ifp->lock);
        if (ifp->state == INET6_IFADDR_STATE_DEAD) {
                spin_unlock(&ifp->lock);