netdev - Re: [PATCH net] kcm: do not attach PF

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Date:   Wed, 30 Aug 2017 09:42:52 -0700
From:   Tom Herbert <tom@...ntonium.net>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] kcm: do not attach PF_KCM sockets to avoid deadlock

On Wed, Aug 30, 2017 at 9:29 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> syzkaller had no problem to trigger a deadlock, attaching a KCM socket
> to another one (or itself). (original syzkaller report was a very
> confusing lockdep splat during a sendmsg())
>
> It seems KCM claims to only support TCP, but no enforcement is done,
> so we might need to add additional checks.
>
> Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>

Acked-by: Tom Herbert <tom@...ntonium.net>

> ---
>  net/kcm/kcmsock.c |    4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
> index 48e993b2dbcf1afae04968ed840e2e98c2cf6772..af4e76ac88ff0817398d1d7460a41f0cd5fe6f30 100644
> --- a/net/kcm/kcmsock.c
> +++ b/net/kcm/kcmsock.c
> @@ -1387,6 +1387,10 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
>         if (!csk)
>                 return -EINVAL;
>
> +       /* We must prevent loops or risk deadlock ! */
> +       if (csk->sk_family == PF_KCM)
> +               return -EOPNOTSUPP;
> +
>         psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL);
>         if (!psock)
>                 return -ENOMEM;
>
>