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![Xie He](/assets/img/avatar_default.png)
When sending a packet, we will prepend it with an LAPB header.
This modifies the shared parts of a cloned skb, so we should copy the
skb rather than just clone it, before we prepend the header.
In "Documentation/networking/driver.rst" (the 2nd point), it states
that drivers shouldn't modify the shared parts of a cloned skb when
transmitting.
The "dev_queue_xmit_nit" function in "net/core/dev.c", which is called
when an skb is being sent, clones the skb and sents the clone to
AF_PACKET sockets. Because the LAPB drivers first remove a 1-byte
pseudo-header before handing over the skb to us, if we don't copy the
skb before prepending the LAPB header, the first byte of the packets
received on AF_PACKET sockets can be corrupted.
Fixes: 1da177e4c3
("Linux-2.6.12-rc2")
Signed-off-by: Xie He <xie.he.0141@gmail.com>
Acked-by: Martin Schiller <ms@dev.tdt.de>
Link: https://lore.kernel.org/r/20210201055706.415842-1-xie.he.0141@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
205 lines
4.7 KiB
C
205 lines
4.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* LAPB release 002
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*
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* This code REQUIRES 2.1.15 or higher/ NET3.038
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*
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* History
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* LAPB 001 Jonathan Naylor Started Coding
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* LAPB 002 Jonathan Naylor New timer architecture.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/errno.h>
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#include <linux/types.h>
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#include <linux/socket.h>
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#include <linux/in.h>
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#include <linux/kernel.h>
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#include <linux/timer.h>
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#include <linux/string.h>
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#include <linux/sockios.h>
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#include <linux/net.h>
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#include <linux/inet.h>
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#include <linux/skbuff.h>
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#include <linux/slab.h>
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#include <net/sock.h>
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#include <linux/uaccess.h>
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#include <linux/fcntl.h>
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#include <linux/mm.h>
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#include <linux/interrupt.h>
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#include <net/lapb.h>
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/*
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* This procedure is passed a buffer descriptor for an iframe. It builds
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* the rest of the control part of the frame and then writes it out.
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*/
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static void lapb_send_iframe(struct lapb_cb *lapb, struct sk_buff *skb, int poll_bit)
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{
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unsigned char *frame;
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if (!skb)
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return;
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if (lapb->mode & LAPB_EXTENDED) {
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frame = skb_push(skb, 2);
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frame[0] = LAPB_I;
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frame[0] |= lapb->vs << 1;
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frame[1] = poll_bit ? LAPB_EPF : 0;
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frame[1] |= lapb->vr << 1;
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} else {
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frame = skb_push(skb, 1);
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*frame = LAPB_I;
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*frame |= poll_bit ? LAPB_SPF : 0;
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*frame |= lapb->vr << 5;
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*frame |= lapb->vs << 1;
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}
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lapb_dbg(1, "(%p) S%d TX I(%d) S%d R%d\n",
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lapb->dev, lapb->state, poll_bit, lapb->vs, lapb->vr);
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lapb_transmit_buffer(lapb, skb, LAPB_COMMAND);
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}
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void lapb_kick(struct lapb_cb *lapb)
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{
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struct sk_buff *skb, *skbn;
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unsigned short modulus, start, end;
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modulus = (lapb->mode & LAPB_EXTENDED) ? LAPB_EMODULUS : LAPB_SMODULUS;
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start = !skb_peek(&lapb->ack_queue) ? lapb->va : lapb->vs;
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end = (lapb->va + lapb->window) % modulus;
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if (!(lapb->condition & LAPB_PEER_RX_BUSY_CONDITION) &&
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start != end && skb_peek(&lapb->write_queue)) {
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lapb->vs = start;
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/*
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* Dequeue the frame and copy it.
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*/
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skb = skb_dequeue(&lapb->write_queue);
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do {
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skbn = skb_copy(skb, GFP_ATOMIC);
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if (!skbn) {
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skb_queue_head(&lapb->write_queue, skb);
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break;
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}
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if (skb->sk)
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skb_set_owner_w(skbn, skb->sk);
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/*
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* Transmit the frame copy.
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*/
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lapb_send_iframe(lapb, skbn, LAPB_POLLOFF);
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lapb->vs = (lapb->vs + 1) % modulus;
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/*
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* Requeue the original data frame.
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*/
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skb_queue_tail(&lapb->ack_queue, skb);
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} while (lapb->vs != end && (skb = skb_dequeue(&lapb->write_queue)) != NULL);
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lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
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if (!lapb_t1timer_running(lapb))
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lapb_start_t1timer(lapb);
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}
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}
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void lapb_transmit_buffer(struct lapb_cb *lapb, struct sk_buff *skb, int type)
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{
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unsigned char *ptr;
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ptr = skb_push(skb, 1);
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if (lapb->mode & LAPB_MLP) {
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if (lapb->mode & LAPB_DCE) {
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if (type == LAPB_COMMAND)
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*ptr = LAPB_ADDR_C;
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if (type == LAPB_RESPONSE)
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*ptr = LAPB_ADDR_D;
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} else {
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if (type == LAPB_COMMAND)
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*ptr = LAPB_ADDR_D;
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if (type == LAPB_RESPONSE)
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*ptr = LAPB_ADDR_C;
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}
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} else {
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if (lapb->mode & LAPB_DCE) {
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if (type == LAPB_COMMAND)
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*ptr = LAPB_ADDR_A;
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if (type == LAPB_RESPONSE)
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*ptr = LAPB_ADDR_B;
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} else {
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if (type == LAPB_COMMAND)
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*ptr = LAPB_ADDR_B;
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if (type == LAPB_RESPONSE)
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*ptr = LAPB_ADDR_A;
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}
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}
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lapb_dbg(2, "(%p) S%d TX %3ph\n", lapb->dev, lapb->state, skb->data);
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if (!lapb_data_transmit(lapb, skb))
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kfree_skb(skb);
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}
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void lapb_establish_data_link(struct lapb_cb *lapb)
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{
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lapb->condition = 0x00;
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lapb->n2count = 0;
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if (lapb->mode & LAPB_EXTENDED) {
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lapb_dbg(1, "(%p) S%d TX SABME(1)\n", lapb->dev, lapb->state);
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lapb_send_control(lapb, LAPB_SABME, LAPB_POLLON, LAPB_COMMAND);
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} else {
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lapb_dbg(1, "(%p) S%d TX SABM(1)\n", lapb->dev, lapb->state);
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lapb_send_control(lapb, LAPB_SABM, LAPB_POLLON, LAPB_COMMAND);
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}
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lapb_start_t1timer(lapb);
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lapb_stop_t2timer(lapb);
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}
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void lapb_enquiry_response(struct lapb_cb *lapb)
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{
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lapb_dbg(1, "(%p) S%d TX RR(1) R%d\n",
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lapb->dev, lapb->state, lapb->vr);
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lapb_send_control(lapb, LAPB_RR, LAPB_POLLON, LAPB_RESPONSE);
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lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
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}
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void lapb_timeout_response(struct lapb_cb *lapb)
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{
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lapb_dbg(1, "(%p) S%d TX RR(0) R%d\n",
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lapb->dev, lapb->state, lapb->vr);
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lapb_send_control(lapb, LAPB_RR, LAPB_POLLOFF, LAPB_RESPONSE);
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lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
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}
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void lapb_check_iframes_acked(struct lapb_cb *lapb, unsigned short nr)
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{
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if (lapb->vs == nr) {
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lapb_frames_acked(lapb, nr);
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lapb_stop_t1timer(lapb);
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lapb->n2count = 0;
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} else if (lapb->va != nr) {
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lapb_frames_acked(lapb, nr);
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lapb_start_t1timer(lapb);
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}
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}
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void lapb_check_need_response(struct lapb_cb *lapb, int type, int pf)
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{
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if (type == LAPB_COMMAND && pf)
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lapb_enquiry_response(lapb);
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}
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