netdev - Re: [PATCH net] l2tp: add sk_family checks to l2tp_validate

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Message-ID: <20200530155136.GA31596@pc-3.home>
Date:   Sat, 30 May 2020 17:51:36 +0200
From:   Guillaume Nault <gnault@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        James Chapman <jchapman@...alix.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] l2tp: add sk_family checks to l2tp_validate_socket

On Fri, May 29, 2020 at 11:32:25AM -0700, Eric Dumazet wrote:
> syzbot was able to trigger a crash after using an ISDN socket
> and fool l2tp.
> 
> Fix this by making sure the UDP socket is of the proper family.
> 
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -1458,6 +1458,9 @@ static int l2tp_validate_socket(const struct sock *sk, const struct net *net,
>  	if (sk->sk_type != SOCK_DGRAM)
>  		return -EPROTONOSUPPORT;
>  
> +	if (sk->sk_family != PF_INET && sk->sk_family != PF_INET6)
> +		return -EPROTONOSUPPORT;
> +
>  	if ((encap == L2TP_ENCAPTYPE_UDP && sk->sk_protocol != IPPROTO_UDP) ||
>  	    (encap == L2TP_ENCAPTYPE_IP && sk->sk_protocol != IPPROTO_L2TP))
>  		return -EPROTONOSUPPORT;
> 
Thanks a lot!

Acked-by: Guillaume Nault <gnault@...hat.com>