linux-kernel - Re: [PATCH] net: initialize local variables in net/ipv6/mcast.c and net/ipv4/igmp.c

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Date:   Fri, 2 Apr 2021 23:12:36 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Phillip Potter <phil@...lpotter.co.uk>
Cc:     davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: initialize local variables in net/ipv6/mcast.c and
 net/ipv4/igmp.c



On 4/2/21 10:53 PM, Eric Dumazet wrote:
> 
> 
> On 4/2/21 8:10 PM, Phillip Potter wrote:
>> On Fri, Apr 02, 2021 at 07:49:44PM +0200, Eric Dumazet wrote:
>>>
>>>
>>> On 4/2/21 7:36 PM, Phillip Potter wrote:
>>>> Use memset to initialize two local buffers in net/ipv6/mcast.c,
>>>> and another in net/ipv4/igmp.c. Fixes a KMSAN found uninit-value
>>>> bug reported by syzbot at:
>>>> https://syzkaller.appspot.com/bug?id=0766d38c656abeace60621896d705743aeefed51
>>>
>>>
>>> According to this link, the bug no longer triggers.
>>>
>>> Please explain why you think it is still there.
>>>
>>
>> Dear Eric,
>>
>> It definitely still triggers, tested it on the master branch of
>> https://github.com/google/kmsan last night. The patch which fixes the
>> crash on that page is the same patch I've sent in.
> 
> Please send the full report (stack trace)

I think your patch just silences the real problem.

The issue at hand is that TUNSETLINK changes dev->type without making
any change to dev->addr_len

This is the real issue.

If you care about this, please fix tun driver.