sctp: do not allow the v4 socket to bind a v4mapped v6 address

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index feb2ca69827a7d9584db3e2dd2cdf68d99479b4d..039fcb618c34985f5b2a337d6a0876bca24b28da 100644 (file)
--- 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);