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

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Date:   Sat, 3 Apr 2021 20:41:15 +0100
From:   Phillip Potter <phil@...lpotter.co.uk>
To:     Eric Dumazet <eric.dumazet@...il.com>
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 Fri, Apr 02, 2021 at 11:12:36PM +0200, Eric Dumazet wrote:
> 
> 
> 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.
> 

Dear Eric,

Thank you for pointing me in the right direction. I will do as you
suggest.

Regards,
Phil