[PATCH net] sctp: check af before verify address in sctp_addr_id2transport

[Xin Long]

Commit 6f29a1306131 ("sctp: sctp_addr_id2transport should verify the
addr before looking up assoc") invoked sctp_verify_addr to verify the
addr.

But it didn't check af variable beforehand, once users pass an address
with family = 0 through sockopt, sctp_get_af_specific will return NULL
and NULL pointer dereference will be caused by af->sockaddr_len.

This patch is to fix it by returning NULL if af variable is NULL.

Fixes: 6f29a1306131 ("sctp: sctp_addr_id2transport should verify the addr 
before looking up assoc")
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/sctp/socket.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 37eeab7..f354375 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -239,7 +239,7 @@ static struct sctp_transport *sctp_addr_id2transport(struct 
sock *sk,
        union sctp_addr *laddr = (union sctp_addr *)addr;
        struct sctp_transport *transport;
 
-       if (sctp_verify_addr(sk, laddr, af->sockaddr_len))
+       if (!af || sctp_verify_addr(sk, laddr, af->sockaddr_len))
                return NULL;
 
        addr_asoc = sctp_endpoint_lookup_assoc(sctp_sk(sk)->ep,
-- 
2.1.0