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7b3ba18703
LLC reads the mac header with eth_hdr without verifying that the skb
has an Ethernet header.
Syzbot was able to enter llc_rcv on a tun device. Tun can insert
packets without mac len and with user configurable skb->protocol
(passing a tun_pi header when not configuring IFF_NO_PI).
BUG: KMSAN: uninit-value in llc_station_ac_send_test_r net/llc/llc_station.c:81 [inline]
BUG: KMSAN: uninit-value in llc_station_rcv+0x6fb/0x1290 net/llc/llc_station.c:111
llc_station_ac_send_test_r net/llc/llc_station.c:81 [inline]
llc_station_rcv+0x6fb/0x1290 net/llc/llc_station.c:111
llc_rcv+0xc5d/0x14a0 net/llc/llc_input.c:218
__netif_receive_skb_one_core net/core/dev.c:5523 [inline]
__netif_receive_skb+0x1a6/0x5a0 net/core/dev.c:5637
netif_receive_skb_internal net/core/dev.c:5723 [inline]
netif_receive_skb+0x58/0x660 net/core/dev.c:5782
tun_rx_batched+0x3ee/0x980 drivers/net/tun.c:1555
tun_get_user+0x54c5/0x69c0 drivers/net/tun.c:2002
Add a mac_len test before all three eth_hdr(skb) calls under net/llc.
There are further uses in include/net/llc_pdu.h. All these are
protected by a test skb->protocol == ETH_P_802_2. Which does not
protect against this tun scenario.
But the mac_len test added in this patch in llc_fixup_skb will
indirectly protect those too. That is called from llc_rcv before any
other LLC code.
It is tempting to just add a blanket mac_len check in llc_rcv, but
not sure whether that could break valid LLC paths that do not assume
an Ethernet header. 802.2 LLC may be used on top of non-802.3
protocols in principle. The below referenced commit shows that used
to, on top of Token Ring.
At least one of the three eth_hdr uses goes back to before the start
of git history. But the one that syzbot exercises is introduced in
this commit. That commit is old enough (2008), that effectively all
stable kernels should receive this.
Fixes: f83f1768f8 ("[LLC]: skb allocation size for responses")
Reported-by: syzbot+a8c7be6dee0de1b669cc@syzkaller.appspotmail.com
Signed-off-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20231025234251.3796495-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
127 lines
3.2 KiB
C
127 lines
3.2 KiB
C
/*
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* llc_station.c - station component of LLC
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*
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* Copyright (c) 1997 by Procom Technology, Inc.
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* 2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
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*
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* This program can be redistributed or modified under the terms of the
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* GNU General Public License as published by the Free Software Foundation.
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* This program is distributed without any warranty or implied warranty
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* of merchantability or fitness for a particular purpose.
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*
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* See the GNU General Public License for more details.
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*/
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <net/llc.h>
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#include <net/llc_sap.h>
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#include <net/llc_conn.h>
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#include <net/llc_c_ac.h>
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#include <net/llc_s_ac.h>
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#include <net/llc_c_ev.h>
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#include <net/llc_c_st.h>
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#include <net/llc_s_ev.h>
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#include <net/llc_s_st.h>
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#include <net/llc_pdu.h>
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static int llc_stat_ev_rx_null_dsap_xid_c(struct sk_buff *skb)
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{
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struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
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return LLC_PDU_IS_CMD(pdu) && /* command PDU */
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LLC_PDU_TYPE_IS_U(pdu) && /* U type PDU */
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LLC_U_PDU_CMD(pdu) == LLC_1_PDU_CMD_XID &&
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!pdu->dsap; /* NULL DSAP value */
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}
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static int llc_stat_ev_rx_null_dsap_test_c(struct sk_buff *skb)
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{
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struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
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return LLC_PDU_IS_CMD(pdu) && /* command PDU */
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LLC_PDU_TYPE_IS_U(pdu) && /* U type PDU */
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LLC_U_PDU_CMD(pdu) == LLC_1_PDU_CMD_TEST &&
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!pdu->dsap; /* NULL DSAP */
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}
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static int llc_station_ac_send_xid_r(struct sk_buff *skb)
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{
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u8 mac_da[ETH_ALEN], dsap;
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int rc = 1;
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struct sk_buff *nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U,
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sizeof(struct llc_xid_info));
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if (!nskb)
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goto out;
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llc_pdu_decode_sa(skb, mac_da);
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llc_pdu_decode_ssap(skb, &dsap);
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llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, 0, dsap, LLC_PDU_RSP);
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llc_pdu_init_as_xid_rsp(nskb, LLC_XID_NULL_CLASS_2, 127);
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rc = llc_mac_hdr_init(nskb, skb->dev->dev_addr, mac_da);
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if (unlikely(rc))
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goto free;
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dev_queue_xmit(nskb);
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out:
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return rc;
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free:
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kfree_skb(nskb);
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goto out;
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}
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static int llc_station_ac_send_test_r(struct sk_buff *skb)
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{
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u8 mac_da[ETH_ALEN], dsap;
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int rc = 1;
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u32 data_size;
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struct sk_buff *nskb;
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if (skb->mac_len < ETH_HLEN)
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goto out;
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/* The test request command is type U (llc_len = 3) */
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data_size = ntohs(eth_hdr(skb)->h_proto) - 3;
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nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U, data_size);
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if (!nskb)
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goto out;
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llc_pdu_decode_sa(skb, mac_da);
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llc_pdu_decode_ssap(skb, &dsap);
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llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, 0, dsap, LLC_PDU_RSP);
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llc_pdu_init_as_test_rsp(nskb, skb);
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rc = llc_mac_hdr_init(nskb, skb->dev->dev_addr, mac_da);
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if (unlikely(rc))
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goto free;
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dev_queue_xmit(nskb);
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out:
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return rc;
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free:
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kfree_skb(nskb);
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goto out;
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}
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/**
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* llc_station_rcv - send received pdu to the station state machine
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* @skb: received frame.
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*
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* Sends data unit to station state machine.
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*/
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static void llc_station_rcv(struct sk_buff *skb)
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{
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if (llc_stat_ev_rx_null_dsap_xid_c(skb))
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llc_station_ac_send_xid_r(skb);
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else if (llc_stat_ev_rx_null_dsap_test_c(skb))
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llc_station_ac_send_test_r(skb);
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kfree_skb(skb);
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}
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void __init llc_station_init(void)
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{
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llc_set_station_handler(llc_station_rcv);
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}
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void llc_station_exit(void)
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{
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llc_set_station_handler(NULL);
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}
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