netdev - Re: [Bug 199643] New: UBSAN: Undefined behaviour in ./include/net/route.h:240:2

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Date:   Thu, 7 Jun 2018 18:02:33 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc:     David Ahern <dsahern@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>, stephen@...workplumber.org,
        netdev@...r.kernel.org
Subject: Re: [Bug 199643] New: UBSAN: Undefined behaviour in
 ./include/net/route.h:240:2

CC: Andrey

On Thu, 7 Jun 2018 17:53:35 -0700, David Ahern wrote:
> On 6/7/18 5:49 PM, Jakub Kicinski wrote:
> > On Thu, 7 Jun 2018 17:28:59 -0700, Eric Dumazet wrote:  
> >> On 06/07/2018 05:11 PM, David Miller wrote:  
> >>> From: Jakub Kicinski <jakub.kicinski@...ronome.com>
> >>> Date: Thu, 7 Jun 2018 17:06:23 -0700
> >>>     
> >>>> [  293.213661]  ip_send_unicast_reply+0x1b67/0x1d0e    
> >>>
> >>> This calls ip_setup_cork() which can NULL out the 'rt' route
> >>> pointer.  Hmmm... :-/
> >>
> >> UBSAN seems unhappy  with dst being NULL in :
> >>
> >> dst_release(&rt->dst);
> >>
> >> But the code obviously is ready for dst being NULL, it is even documented :)  
> > 
> > Oh, so the code depends on dst being the first member?  Would it make
> > sense to just cast the pointer instead?
> >   
> 
> I've been going the other way with 'rt to dst' and 'dst to rt'
> transformations.
> 
> Perhaps UBSAN should be updated to understand that NULL + 0 is ok.