netdev - Re: Race Condition Observed in ARP Processing.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Fri, 1 Jan 2021 23:40:10 +0530
From:   Chinmay Agarwal <chinagar@...eaurora.org>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: Race Condition Observed in ARP Processing.

Sure, will raise a patch post testing.

On Thu, Dec 31, 2020 at 10:53:59AM -0800, Cong Wang wrote:
> On Tue, Dec 29, 2020 at 8:06 AM Chinmay Agarwal <chinagar@...eaurora.org> wrote:
> >
> > Hi All,
> >
> > We found a crash while performing some automated stress tests on a 5.4 kernel based device.
> >
> > We found out that it there is a freed neighbour address which was still part of the gc_list and was leading to crash.
> > Upon adding some debugs and checking neigh_put/neigh_hold/neigh_destroy calls stacks, looks like there is a possibility of a Race condition happening in the code.
> [...]
> > The crash may have been due to out of order ARP replies.
> > As neighbour is marked dead should we go ahead with updating our ARP Tables?
> 
> I think you are probably right, we should just do unlock and return
> in __neigh_update() when hitting if (neigh->dead) branch. Something
> like below:
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 9500d28a43b0..0ce592f585c8 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -1250,6 +1250,7 @@ static int __neigh_update(struct neighbour
> *neigh, const u8 *lladdr,
>                 goto out;
>         if (neigh->dead) {
>                 NL_SET_ERR_MSG(extack, "Neighbor entry is now dead");
> +               new = old;
>                 goto out;
>         }
> 
> But given the old state probably contains NUD_PERMANENT, I guess
> you hit the following branch instead:
> 
>         if (!(flags & NEIGH_UPDATE_F_ADMIN) &&
>             (old & (NUD_NOARP | NUD_PERMANENT)))
>                 goto out;
> 
> So we may have to check ->dead before this. Please double check.
> 
> This bug is probably introduced by commit 9c29a2f55ec05cc8b525ee.
> Can you make a patch and send it out formally after testing?
> 
> Thanks!