net: sctp: fix NULL pointer dereference in af->from_addr_param on malformed packet

An SCTP server doing ASCONF will panic on malformed INIT ping-of-death
in the form of:

  ------------ INIT[PARAM: SET_PRIMARY_IP] ------------>

While the INIT chunk parameter verification dissects through many things
in order to detect malformed input, it misses to actually check parameters
inside of parameters. E.g. RFC5061, section 4.2.4 proposes a 'set primary
IP address' parameter in ASCONF, which has as a subparameter an address
parameter.

So an attacker may send a parameter type other than SCTP_PARAM_IPV4_ADDRESS
or SCTP_PARAM_IPV6_ADDRESS, param_type2af() will subsequently return 0
and thus sctp_get_af_specific() returns NULL, too, which we then happily
dereference unconditionally through af->from_addr_param().

The trace for the log:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000078
IP: [<ffffffffa01e9c62>] sctp_process_init+0x492/0x990 [sctp]
PGD 0
Oops: 0000 [#1] SMP
[...]
Pid: 0, comm: swapper Not tainted 2.6.32-504.el6.x86_64 #1 Bochs Bochs
RIP: 0010:[<ffffffffa01e9c62>]  [<ffffffffa01e9c62>] sctp_process_init+0x492/0x990 [sctp]
[...]
Call Trace:
 <IRQ>
 [<ffffffffa01f2add>] ? sctp_bind_addr_copy+0x5d/0xe0 [sctp]
 [<ffffffffa01e1fcb>] sctp_sf_do_5_1B_init+0x21b/0x340 [sctp]
 [<ffffffffa01e3751>] sctp_do_sm+0x71/0x1210 [sctp]
 [<ffffffffa01e5c09>] ? sctp_endpoint_lookup_assoc+0xc9/0xf0 [sctp]
 [<ffffffffa01e61f6>] sctp_endpoint_bh_rcv+0x116/0x230 [sctp]
 [<ffffffffa01ee986>] sctp_inq_push+0x56/0x80 [sctp]
 [<ffffffffa01fcc42>] sctp_rcv+0x982/0xa10 [sctp]
 [<ffffffffa01d5123>] ? ipt_local_in_hook+0x23/0x28 [iptable_filter]
 [<ffffffff8148bdc9>] ? nf_iterate+0x69/0xb0
 [<ffffffff81496d10>] ? ip_local_deliver_finish+0x0/0x2d0
 [<ffffffff8148bf86>] ? nf_hook_slow+0x76/0x120
 [<ffffffff81496d10>] ? ip_local_deliver_finish+0x0/0x2d0
[...]

A minimal way to address this is to check for NULL as we do on all
other such occasions where we know sctp_get_af_specific() could
possibly return with NULL.

Fixes: d6de3097592b ("[SCTP]: Add the handling of "Set Primary IP Address" parameter to INIT")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
int sctp_process_asconf_ack(struct sctp_association *asoc,
			    struct sctp_chunk *asconf_ack)
{
	struct sctp_chunk	*asconf = asoc->addip_last_asconf;
	union sctp_addr_param	*addr_param;
	sctp_addip_param_t	*asconf_param;
	int	length = 0;
	int	asconf_len = asconf->skb->len;
	int	all_param_pass = 0;
	int	no_err = 1;
	int	retval = 0;
	__be16	err_code = SCTP_ERROR_NO_ERROR;

	/* Skip the chunkhdr and addiphdr from the last asconf sent and store
	 * a pointer to address parameter.
	 */
	length = sizeof(sctp_addip_chunk_t);
	addr_param = (union sctp_addr_param *)(asconf->skb->data + length);
	asconf_len -= length;

	/* Skip the address parameter in the last asconf sent and store a
	 * pointer to the first asconf parameter.
	 */
	length = ntohs(addr_param->p.length);
	asconf_param = (void *)addr_param + length;
	asconf_len -= length;

	/* ADDIP 4.1
	 * A8) If there is no response(s) to specific TLV parameter(s), and no
	 * failures are indicated, then all request(s) are considered
	 * successful.
	 */
	if (asconf_ack->skb->len == sizeof(sctp_addiphdr_t))
		all_param_pass = 1;

	/* Process the TLVs contained in the last sent ASCONF chunk. */
	while (asconf_len > 0) {
		if (all_param_pass)
			err_code = SCTP_ERROR_NO_ERROR;
		else {
			err_code = sctp_get_asconf_response(asconf_ack,
							    asconf_param,
							    no_err);
			if (no_err && (SCTP_ERROR_NO_ERROR != err_code))
				no_err = 0;
		}

		switch (err_code) {
		case SCTP_ERROR_NO_ERROR:
			sctp_asconf_param_success(asoc, asconf_param);
			break;

		case SCTP_ERROR_RSRC_LOW:
			retval = 1;
			break;

		case SCTP_ERROR_UNKNOWN_PARAM:
			/* Disable sending this type of asconf parameter in
			 * future.
			 */
			asoc->peer.addip_disabled_mask |=
				asconf_param->param_hdr.type;
			break;

		case SCTP_ERROR_REQ_REFUSED:
		case SCTP_ERROR_DEL_LAST_IP:
		case SCTP_ERROR_DEL_SRC_IP:
		default:
			 break;
		}

		/* Skip the processed asconf parameter and move to the next
		 * one.
		 */
		length = ntohs(asconf_param->param_hdr.length);
		asconf_param = (void *)asconf_param + length;
		asconf_len -= length;
	}

	if (no_err && asoc->src_out_of_asoc_ok) {
		asoc->src_out_of_asoc_ok = 0;
		sctp_transport_immediate_rtx(asoc->peer.primary_path);
	}

	/* Free the cached last sent asconf chunk. */
	list_del_init(&asconf->transmitted_list);
	sctp_chunk_free(asconf);
	asoc->addip_last_asconf = NULL;

	return retval;
}

int sctp_process_asconf_ack(struct sctp_association *asoc,
			    struct sctp_chunk *asconf_ack)
{
	struct sctp_chunk	*asconf = asoc->addip_last_asconf;
	union sctp_addr_param	*addr_param;
	sctp_addip_param_t	*asconf_param;
	int	length = 0;
	int	asconf_len = asconf->skb->len;
	int	all_param_pass = 0;
	int	no_err = 1;
	int	retval = 0;
	__be16	err_code = SCTP_ERROR_NO_ERROR;

	/* Skip the chunkhdr and addiphdr from the last asconf sent and store
	 * a pointer to address parameter.
	 */
	length = sizeof(sctp_addip_chunk_t);
	addr_param = (union sctp_addr_param *)(asconf->skb->data + length);
	asconf_len -= length;

	/* Skip the address parameter in the last asconf sent and store a
	 * pointer to the first asconf parameter.
	 */
	length = ntohs(addr_param->p.length);
	asconf_param = (void *)addr_param + length;
	asconf_len -= length;

	/* ADDIP 4.1
	 * A8) If there is no response(s) to specific TLV parameter(s), and no
	 * failures are indicated, then all request(s) are considered
	 * successful.
	 */
	if (asconf_ack->skb->len == sizeof(sctp_addiphdr_t))
		all_param_pass = 1;

	/* Process the TLVs contained in the last sent ASCONF chunk. */
	while (asconf_len > 0) {
		if (all_param_pass)
			err_code = SCTP_ERROR_NO_ERROR;
		else {
			err_code = sctp_get_asconf_response(asconf_ack,
							    asconf_param,
							    no_err);
			if (no_err && (SCTP_ERROR_NO_ERROR != err_code))
				no_err = 0;
		}

		switch (err_code) {
		case SCTP_ERROR_NO_ERROR:
			sctp_asconf_param_success(asoc, asconf_param);
			break;

		case SCTP_ERROR_RSRC_LOW:
			retval = 1;
			break;

		case SCTP_ERROR_UNKNOWN_PARAM:
			/* Disable sending this type of asconf parameter in
			 * future.
			 */
			asoc->peer.addip_disabled_mask |=
				asconf_param->param_hdr.type;
			break;

		case SCTP_ERROR_REQ_REFUSED:
		case SCTP_ERROR_DEL_LAST_IP:
		case SCTP_ERROR_DEL_SRC_IP:
		default:
			 break;
		}

		/* Skip the processed asconf parameter and move to the next
		 * one.
		 */
		length = ntohs(asconf_param->param_hdr.length);
		asconf_param = (void *)asconf_param + length;
		asconf_len -= length;
	}

	if (no_err && asoc->src_out_of_asoc_ok) {
		asoc->src_out_of_asoc_ok = 0;
		sctp_transport_immediate_rtx(asoc->peer.primary_path);
	}

	/* Free the cached last sent asconf chunk. */
	list_del_init(&asconf->transmitted_list);
	sctp_chunk_free(asconf);
	asoc->addip_last_asconf = NULL;

	return retval;
}
