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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
> Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> ---
> 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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