Re: [PATCH net] sctp: do not allow the v4 socket to bind a v4mapped v6 address

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Mon, Jan 15, 2018 at 05:02:00PM +0800, Xin Long wrote:
> The check in sctp_sockaddr_af is not robust enough to forbid binding a
> v4mapped v6 addr on a v4 socket.
> 
> The worse thing is that v4 socket's bind_verify would not convert this
> v4mapped v6 addr to a v4 addr. syzbot even reported a crash as the v4
> socket bound a v6 addr.
> 
> This patch is to fix it by doing the common sa.sa_family check first,
> then AF_INET check for v4mapped v6 addrs.
> 
> Fixes: 7dab83de50c7 ("sctp: Support ipv6only AF_INET6 sockets.")
> Reported-by: syzbot+7b7b518b1228d2743963@syzkaller.appspotmail.com
> Acked-by: Neil Horman <nhorman@tuxdriver.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

> ---
>  net/sctp/socket.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index feb2ca6..039fcb6 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -335,16 +335,14 @@ static struct sctp_af *sctp_sockaddr_af(struct sctp_sock *opt,
>  	if (len < sizeof (struct sockaddr))
>  		return NULL;
>  
> +	if (!opt->pf->af_supported(addr->sa.sa_family, opt))
> +		return NULL;
> +
>  	/* V4 mapped address are really of AF_INET family */
>  	if (addr->sa.sa_family = AF_INET6 &&
> -	    ipv6_addr_v4mapped(&addr->v6.sin6_addr)) {
> -		if (!opt->pf->af_supported(AF_INET, opt))
> -			return NULL;
> -	} else {
> -		/* Does this PF support this AF? */
> -		if (!opt->pf->af_supported(addr->sa.sa_family, opt))
> -			return NULL;
> -	}
> +	    ipv6_addr_v4mapped(&addr->v6.sin6_addr) &&
> +	    !opt->pf->af_supported(AF_INET, opt))
> +		return NULL;
>  
>  	/* If we get this far, af is valid. */
>  	af = sctp_get_af_specific(addr->sa.sa_family);
> -- 
> 2.1.0
> 
> --
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