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linux/net/llc/llc_s_ac.c
Pavel Skripkin c7c9d2102c net: llc: fix skb_over_panic 
Syzbot reported skb_over_panic() in llc_pdu_init_as_xid_cmd(). The
problem was in wrong LCC header manipulations.

Syzbot's reproducer tries to send XID packet. llc_ui_sendmsg() is
doing following steps:

	1. skb allocation with size = len + header size
		len is passed from userpace and header size
		is 3 since addr->sllc_xid is set.

	2. skb_reserve() for header_len = 3
	3. filling all other space with memcpy_from_msg()

Ok, at this moment we have fully loaded skb, only headers needs to be
filled.

Then code comes to llc_sap_action_send_xid_c(). This function pushes 3
bytes for LLC PDU header and initializes it. Then comes
llc_pdu_init_as_xid_cmd(). It initalizes next 3 bytes *AFTER* LLC PDU
header and call skb_push(skb, 3). This looks wrong for 2 reasons:

	1. Bytes rigth after LLC header are user data, so this function
	   was overwriting payload.

	2. skb_push(skb, 3) call can cause skb_over_panic() since
	   all free space was filled in llc_ui_sendmsg(). (This can
	   happen is user passed 686 len: 686 + 14 (eth header) + 3 (LLC
	   header) = 703. SKB_DATA_ALIGN(703) = 704)

So, in this patch I added 2 new private constansts: LLC_PDU_TYPE_U_XID
and LLC_PDU_LEN_U_XID. LLC_PDU_LEN_U_XID is used to correctly reserve
header size to handle LLC + XID case. LLC_PDU_TYPE_U_XID is used by
llc_pdu_header_init() function to push 6 bytes instead of 3. And finally
I removed skb_push() call from llc_pdu_init_as_xid_cmd().

This changes should not affect other parts of LLC, since after
all steps we just transmit buffer.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Reported-and-tested-by: syzbot+5e5a981ad7cc54c4b2b4@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2021-07-27 13:05:56 +01:00

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/*
* llc_s_ac.c - actions performed during sap state transition.
*
* Description :
* Functions in this module are implementation of sap component actions.
* Details of actions can be found in IEEE-802.2 standard document.
* All functions have one sap and one event as input argument. All of
* them return 0 On success and 1 otherwise.
*
* Copyright (c) 1997 by Procom Technology, Inc.
* 2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
*
* This program can be redistributed or modified under the terms of the
* GNU General Public License as published by the Free Software Foundation.
* This program is distributed without any warranty or implied warranty
* of merchantability or fitness for a particular purpose.
*
* See the GNU General Public License for more details.
*/
#include <linux/netdevice.h>
#include <net/llc.h>
#include <net/llc_pdu.h>
#include <net/llc_s_ac.h>
#include <net/llc_s_ev.h>
#include <net/llc_sap.h>
/**
* llc_sap_action_unitdata_ind - forward UI PDU to network layer
* @sap: SAP
* @skb: the event to forward
*
* Received a UI PDU from MAC layer; forward to network layer as a
* UNITDATA INDICATION; verify our event is the kind we expect
*/
int llc_sap_action_unitdata_ind(struct llc_sap *sap, struct sk_buff *skb)
{
llc_sap_rtn_pdu(sap, skb);
return 0;
}
/**
* llc_sap_action_send_ui - sends UI PDU resp to UNITDATA REQ to MAC layer
* @sap: SAP
* @skb: the event to send
*
* Sends a UI PDU to the MAC layer in response to a UNITDATA REQUEST
* primitive from the network layer. Verifies event is a primitive type of
* event. Verify the primitive is a UNITDATA REQUEST.
*/
int llc_sap_action_send_ui(struct llc_sap *sap, struct sk_buff *skb)
{
struct llc_sap_state_ev *ev = llc_sap_ev(skb);
int rc;
llc_pdu_header_init(skb, LLC_PDU_TYPE_U, ev->saddr.lsap,
ev->daddr.lsap, LLC_PDU_CMD);
llc_pdu_init_as_ui_cmd(skb);
rc = llc_mac_hdr_init(skb, ev->saddr.mac, ev->daddr.mac);
if (likely(!rc)) {
skb_get(skb);
rc = dev_queue_xmit(skb);
}
return rc;
}
/**
* llc_sap_action_send_xid_c - send XID PDU as response to XID REQ
* @sap: SAP
* @skb: the event to send
*
* Send a XID command PDU to MAC layer in response to a XID REQUEST
* primitive from the network layer. Verify event is a primitive type
* event. Verify the primitive is a XID REQUEST.
*/
int llc_sap_action_send_xid_c(struct llc_sap *sap, struct sk_buff *skb)
{
struct llc_sap_state_ev *ev = llc_sap_ev(skb);
int rc;
llc_pdu_header_init(skb, LLC_PDU_TYPE_U_XID, ev->saddr.lsap,
ev->daddr.lsap, LLC_PDU_CMD);
llc_pdu_init_as_xid_cmd(skb, LLC_XID_NULL_CLASS_2, 0);
rc = llc_mac_hdr_init(skb, ev->saddr.mac, ev->daddr.mac);
if (likely(!rc)) {
skb_get(skb);
rc = dev_queue_xmit(skb);
}
return rc;
}
/**
* llc_sap_action_send_xid_r - send XID PDU resp to MAC for received XID
* @sap: SAP
* @skb: the event to send
*
* Send XID response PDU to MAC in response to an earlier received XID
* command PDU. Verify event is a PDU type event
*/
int llc_sap_action_send_xid_r(struct llc_sap *sap, struct sk_buff *skb)
{
u8 mac_da[ETH_ALEN], mac_sa[ETH_ALEN], dsap;
int rc = 1;
struct sk_buff *nskb;
llc_pdu_decode_sa(skb, mac_da);
llc_pdu_decode_da(skb, mac_sa);
llc_pdu_decode_ssap(skb, &dsap);
nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U,
sizeof(struct llc_xid_info));
if (!nskb)
goto out;
llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, sap->laddr.lsap, dsap,
LLC_PDU_RSP);
llc_pdu_init_as_xid_rsp(nskb, LLC_XID_NULL_CLASS_2, 0);
rc = llc_mac_hdr_init(nskb, mac_sa, mac_da);
if (likely(!rc))
rc = dev_queue_xmit(nskb);
out:
return rc;
}
/**
* llc_sap_action_send_test_c - send TEST PDU to MAC in resp to TEST REQ
* @sap: SAP
* @skb: the event to send
*
* Send a TEST command PDU to the MAC layer in response to a TEST REQUEST
* primitive from the network layer. Verify event is a primitive type
* event; verify the primitive is a TEST REQUEST.
*/
int llc_sap_action_send_test_c(struct llc_sap *sap, struct sk_buff *skb)
{
struct llc_sap_state_ev *ev = llc_sap_ev(skb);
int rc;
llc_pdu_header_init(skb, LLC_PDU_TYPE_U, ev->saddr.lsap,
ev->daddr.lsap, LLC_PDU_CMD);
llc_pdu_init_as_test_cmd(skb);
rc = llc_mac_hdr_init(skb, ev->saddr.mac, ev->daddr.mac);
if (likely(!rc)) {
skb_get(skb);
rc = dev_queue_xmit(skb);
}
return rc;
}
int llc_sap_action_send_test_r(struct llc_sap *sap, struct sk_buff *skb)
{
u8 mac_da[ETH_ALEN], mac_sa[ETH_ALEN], dsap;
struct sk_buff *nskb;
int rc = 1;
u32 data_size;
llc_pdu_decode_sa(skb, mac_da);
llc_pdu_decode_da(skb, mac_sa);
llc_pdu_decode_ssap(skb, &dsap);
/* The test request command is type U (llc_len = 3) */
data_size = ntohs(eth_hdr(skb)->h_proto) - 3;
nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U, data_size);
if (!nskb)
goto out;
llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, sap->laddr.lsap, dsap,
LLC_PDU_RSP);
llc_pdu_init_as_test_rsp(nskb, skb);
rc = llc_mac_hdr_init(nskb, mac_sa, mac_da);
if (likely(!rc))
rc = dev_queue_xmit(nskb);
out:
return rc;
}
/**
* llc_sap_action_report_status - report data link status to layer mgmt
* @sap: SAP
* @skb: the event to send
*
* Report data link status to layer management. Verify our event is the
* kind we expect.
*/
int llc_sap_action_report_status(struct llc_sap *sap, struct sk_buff *skb)
{
return 0;
}
/**
* llc_sap_action_xid_ind - send XID PDU resp to net layer via XID IND
* @sap: SAP
* @skb: the event to send
*
* Send a XID response PDU to the network layer via a XID INDICATION
* primitive.
*/
int llc_sap_action_xid_ind(struct llc_sap *sap, struct sk_buff *skb)
{
llc_sap_rtn_pdu(sap, skb);
return 0;
}
/**
* llc_sap_action_test_ind - send TEST PDU to net layer via TEST IND
* @sap: SAP
* @skb: the event to send
*
* Send a TEST response PDU to the network layer via a TEST INDICATION
* primitive. Verify our event is a PDU type event.
*/
int llc_sap_action_test_ind(struct llc_sap *sap, struct sk_buff *skb)
{
llc_sap_rtn_pdu(sap, skb);
return 0;
}
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