From: Chinmay Agarwal <chinagar@codeaurora•org>
To: Cong Wang <xiyou.wangcong@gmail•com>
Cc: netdev@vger•kernel.org
Subject: Re: Race Condition Observed in ARP Processing.
Date: Fri, 1 Jan 2021 23:40:10 +0530 [thread overview]
Message-ID: <20210101181009.GA17374@chinagar-linux.qualcomm.com> (raw)
In-Reply-To: <CAM_iQpUFCnmu36L0hwrK+xv9gBWKtcq44nOVGNEyR=o9QDx7Pg@mail.gmail.com>
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@codeaurora•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!
prev parent reply other threads:[~2021-01-01 18:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-29 16:04 Race Condition Observed in ARP Processing Chinmay Agarwal
2020-12-31 18:53 ` Cong Wang
2021-01-01 18:10 ` Chinmay Agarwal [this message]
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