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linux/net/rxrpc/call_event.c
David Howells 2ad6691d98 rxrpc: Fix race between incoming ACK parser and retransmitter
There's a race between the retransmission code and the received ACK parser.
The problem is that the retransmission loop has to drop the lock under
which it is iterating through the transmission buffer in order to transmit
a packet, but whilst the lock is dropped, the ACK parser can crank the Tx
window round and discard the packets from the buffer.

The retransmission code then updated the annotations for the wrong packet
and a later retransmission thought it had to retransmit a packet that
wasn't there, leading to a NULL pointer dereference.

Fix this by:

 (1) Moving the annotation change to before we drop the lock prior to
     transmission.  This means we can't vary the annotation depending on
     the outcome of the transmission, but that's fine - we'll retransmit
     again later if it failed now.

 (2) Skipping the packet if the skb pointer is NULL.

The following oops was seen:

	BUG: kernel NULL pointer dereference, address: 000000000000002d
	Workqueue: krxrpcd rxrpc_process_call
	RIP: 0010:rxrpc_get_skb+0x14/0x8a
	...
	Call Trace:
	 rxrpc_resend+0x331/0x41e
	 ? get_vtime_delta+0x13/0x20
	 rxrpc_process_call+0x3c0/0x4ac
	 process_one_work+0x18f/0x27f
	 worker_thread+0x1a3/0x247
	 ? create_worker+0x17d/0x17d
	 kthread+0xe6/0xeb
	 ? kthread_delayed_work_timer_fn+0x83/0x83
	 ret_from_fork+0x1f/0x30

Fixes: 248f219cb8 ("rxrpc: Rewrite the data and ack handling code")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2020-06-11 18:18:22 -07:00

449 lines
12 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/* Management of Tx window, Tx resend, ACKs and out-of-sequence reception
*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/circ_buf.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/udp.h>
#include <net/sock.h>
#include <net/af_rxrpc.h>
#include "ar-internal.h"
/*
* Propose a PING ACK be sent.
*/
static void rxrpc_propose_ping(struct rxrpc_call *call,
bool immediate, bool background)
{
if (immediate) {
if (background &&
!test_and_set_bit(RXRPC_CALL_EV_PING, &call->events))
rxrpc_queue_call(call);
} else {
unsigned long now = jiffies;
unsigned long ping_at = now + rxrpc_idle_ack_delay;
if (time_before(ping_at, call->ping_at)) {
WRITE_ONCE(call->ping_at, ping_at);
rxrpc_reduce_call_timer(call, ping_at, now,
rxrpc_timer_set_for_ping);
}
}
}
/*
* propose an ACK be sent
*/
static void __rxrpc_propose_ACK(struct rxrpc_call *call, u8 ack_reason,
u32 serial, bool immediate, bool background,
enum rxrpc_propose_ack_trace why)
{
enum rxrpc_propose_ack_outcome outcome = rxrpc_propose_ack_use;
unsigned long expiry = rxrpc_soft_ack_delay;
s8 prior = rxrpc_ack_priority[ack_reason];
/* Pings are handled specially because we don't want to accidentally
* lose a ping response by subsuming it into a ping.
*/
if (ack_reason == RXRPC_ACK_PING) {
rxrpc_propose_ping(call, immediate, background);
goto trace;
}
/* Update DELAY, IDLE, REQUESTED and PING_RESPONSE ACK serial
* numbers, but we don't alter the timeout.
*/
_debug("prior %u %u vs %u %u",
ack_reason, prior,
call->ackr_reason, rxrpc_ack_priority[call->ackr_reason]);
if (ack_reason == call->ackr_reason) {
if (RXRPC_ACK_UPDATEABLE & (1 << ack_reason)) {
outcome = rxrpc_propose_ack_update;
call->ackr_serial = serial;
}
if (!immediate)
goto trace;
} else if (prior > rxrpc_ack_priority[call->ackr_reason]) {
call->ackr_reason = ack_reason;
call->ackr_serial = serial;
} else {
outcome = rxrpc_propose_ack_subsume;
}
switch (ack_reason) {
case RXRPC_ACK_REQUESTED:
if (rxrpc_requested_ack_delay < expiry)
expiry = rxrpc_requested_ack_delay;
if (serial == 1)
immediate = false;
break;
case RXRPC_ACK_DELAY:
if (rxrpc_soft_ack_delay < expiry)
expiry = rxrpc_soft_ack_delay;
break;
case RXRPC_ACK_IDLE:
if (rxrpc_idle_ack_delay < expiry)
expiry = rxrpc_idle_ack_delay;
break;
default:
immediate = true;
break;
}
if (test_bit(RXRPC_CALL_EV_ACK, &call->events)) {
_debug("already scheduled");
} else if (immediate || expiry == 0) {
_debug("immediate ACK %lx", call->events);
if (!test_and_set_bit(RXRPC_CALL_EV_ACK, &call->events) &&
background)
rxrpc_queue_call(call);
} else {
unsigned long now = jiffies, ack_at;
if (call->peer->srtt_us != 0)
ack_at = usecs_to_jiffies(call->peer->srtt_us >> 3);
else
ack_at = expiry;
ack_at += READ_ONCE(call->tx_backoff);
ack_at += now;
if (time_before(ack_at, call->ack_at)) {
WRITE_ONCE(call->ack_at, ack_at);
rxrpc_reduce_call_timer(call, ack_at, now,
rxrpc_timer_set_for_ack);
}
}
trace:
trace_rxrpc_propose_ack(call, why, ack_reason, serial, immediate,
background, outcome);
}
/*
* propose an ACK be sent, locking the call structure
*/
void rxrpc_propose_ACK(struct rxrpc_call *call, u8 ack_reason,
u32 serial, bool immediate, bool background,
enum rxrpc_propose_ack_trace why)
{
spin_lock_bh(&call->lock);
__rxrpc_propose_ACK(call, ack_reason, serial,
immediate, background, why);
spin_unlock_bh(&call->lock);
}
/*
* Handle congestion being detected by the retransmit timeout.
*/
static void rxrpc_congestion_timeout(struct rxrpc_call *call)
{
set_bit(RXRPC_CALL_RETRANS_TIMEOUT, &call->flags);
}
/*
* Perform retransmission of NAK'd and unack'd packets.
*/
static void rxrpc_resend(struct rxrpc_call *call, unsigned long now_j)
{
struct sk_buff *skb;
unsigned long resend_at, rto_j;
rxrpc_seq_t cursor, seq, top;
ktime_t now, max_age, oldest, ack_ts;
int ix;
u8 annotation, anno_type, retrans = 0, unacked = 0;
_enter("{%d,%d}", call->tx_hard_ack, call->tx_top);
rto_j = call->peer->rto_j;
now = ktime_get_real();
max_age = ktime_sub(now, jiffies_to_usecs(rto_j));
spin_lock_bh(&call->lock);
cursor = call->tx_hard_ack;
top = call->tx_top;
ASSERT(before_eq(cursor, top));
if (cursor == top)
goto out_unlock;
/* Scan the packet list without dropping the lock and decide which of
* the packets in the Tx buffer we're going to resend and what the new
* resend timeout will be.
*/
trace_rxrpc_resend(call, (cursor + 1) & RXRPC_RXTX_BUFF_MASK);
oldest = now;
for (seq = cursor + 1; before_eq(seq, top); seq++) {
ix = seq & RXRPC_RXTX_BUFF_MASK;
annotation = call->rxtx_annotations[ix];
anno_type = annotation & RXRPC_TX_ANNO_MASK;
annotation &= ~RXRPC_TX_ANNO_MASK;
if (anno_type == RXRPC_TX_ANNO_ACK)
continue;
skb = call->rxtx_buffer[ix];
rxrpc_see_skb(skb, rxrpc_skb_seen);
if (anno_type == RXRPC_TX_ANNO_UNACK) {
if (ktime_after(skb->tstamp, max_age)) {
if (ktime_before(skb->tstamp, oldest))
oldest = skb->tstamp;
continue;
}
if (!(annotation & RXRPC_TX_ANNO_RESENT))
unacked++;
}
/* Okay, we need to retransmit a packet. */
call->rxtx_annotations[ix] = RXRPC_TX_ANNO_RETRANS | annotation;
retrans++;
trace_rxrpc_retransmit(call, seq, annotation | anno_type,
ktime_to_ns(ktime_sub(skb->tstamp, max_age)));
}
resend_at = nsecs_to_jiffies(ktime_to_ns(ktime_sub(now, oldest)));
resend_at += jiffies + rto_j;
WRITE_ONCE(call->resend_at, resend_at);
if (unacked)
rxrpc_congestion_timeout(call);
/* If there was nothing that needed retransmission then it's likely
* that an ACK got lost somewhere. Send a ping to find out instead of
* retransmitting data.
*/
if (!retrans) {
rxrpc_reduce_call_timer(call, resend_at, now_j,
rxrpc_timer_set_for_resend);
spin_unlock_bh(&call->lock);
ack_ts = ktime_sub(now, call->acks_latest_ts);
if (ktime_to_us(ack_ts) < (call->peer->srtt_us >> 3))
goto out;
rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, true, false,
rxrpc_propose_ack_ping_for_lost_ack);
rxrpc_send_ack_packet(call, true, NULL);
goto out;
}
/* Now go through the Tx window and perform the retransmissions. We
* have to drop the lock for each send. If an ACK comes in whilst the
* lock is dropped, it may clear some of the retransmission markers for
* packets that it soft-ACKs.
*/
for (seq = cursor + 1; before_eq(seq, top); seq++) {
ix = seq & RXRPC_RXTX_BUFF_MASK;
annotation = call->rxtx_annotations[ix];
anno_type = annotation & RXRPC_TX_ANNO_MASK;
if (anno_type != RXRPC_TX_ANNO_RETRANS)
continue;
/* We need to reset the retransmission state, but we need to do
* so before we drop the lock as a new ACK/NAK may come in and
* confuse things
*/
annotation &= ~RXRPC_TX_ANNO_MASK;
annotation |= RXRPC_TX_ANNO_RESENT;
call->rxtx_annotations[ix] = annotation;
skb = call->rxtx_buffer[ix];
if (!skb)
continue;
rxrpc_get_skb(skb, rxrpc_skb_got);
spin_unlock_bh(&call->lock);
if (rxrpc_send_data_packet(call, skb, true) < 0) {
rxrpc_free_skb(skb, rxrpc_skb_freed);
return;
}
if (rxrpc_is_client_call(call))
rxrpc_expose_client_call(call);
rxrpc_free_skb(skb, rxrpc_skb_freed);
spin_lock_bh(&call->lock);
if (after(call->tx_hard_ack, seq))
seq = call->tx_hard_ack;
}
out_unlock:
spin_unlock_bh(&call->lock);
out:
_leave("");
}
/*
* Handle retransmission and deferred ACK/abort generation.
*/
void rxrpc_process_call(struct work_struct *work)
{
struct rxrpc_call *call =
container_of(work, struct rxrpc_call, processor);
rxrpc_serial_t *send_ack;
unsigned long now, next, t;
unsigned int iterations = 0;
rxrpc_see_call(call);
//printk("\n--------------------\n");
_enter("{%d,%s,%lx}",
call->debug_id, rxrpc_call_states[call->state], call->events);
recheck_state:
/* Limit the number of times we do this before returning to the manager */
iterations++;
if (iterations > 5)
goto requeue;
if (test_and_clear_bit(RXRPC_CALL_EV_ABORT, &call->events)) {
rxrpc_send_abort_packet(call);
goto recheck_state;
}
if (call->state == RXRPC_CALL_COMPLETE) {
del_timer_sync(&call->timer);
goto out_put;
}
/* Work out if any timeouts tripped */
now = jiffies;
t = READ_ONCE(call->expect_rx_by);
if (time_after_eq(now, t)) {
trace_rxrpc_timer(call, rxrpc_timer_exp_normal, now);
set_bit(RXRPC_CALL_EV_EXPIRED, &call->events);
}
t = READ_ONCE(call->expect_req_by);
if (call->state == RXRPC_CALL_SERVER_RECV_REQUEST &&
time_after_eq(now, t)) {
trace_rxrpc_timer(call, rxrpc_timer_exp_idle, now);
set_bit(RXRPC_CALL_EV_EXPIRED, &call->events);
}
t = READ_ONCE(call->expect_term_by);
if (time_after_eq(now, t)) {
trace_rxrpc_timer(call, rxrpc_timer_exp_hard, now);
set_bit(RXRPC_CALL_EV_EXPIRED, &call->events);
}
t = READ_ONCE(call->ack_at);
if (time_after_eq(now, t)) {
trace_rxrpc_timer(call, rxrpc_timer_exp_ack, now);
cmpxchg(&call->ack_at, t, now + MAX_JIFFY_OFFSET);
set_bit(RXRPC_CALL_EV_ACK, &call->events);
}
t = READ_ONCE(call->ack_lost_at);
if (time_after_eq(now, t)) {
trace_rxrpc_timer(call, rxrpc_timer_exp_lost_ack, now);
cmpxchg(&call->ack_lost_at, t, now + MAX_JIFFY_OFFSET);
set_bit(RXRPC_CALL_EV_ACK_LOST, &call->events);
}
t = READ_ONCE(call->keepalive_at);
if (time_after_eq(now, t)) {
trace_rxrpc_timer(call, rxrpc_timer_exp_keepalive, now);
cmpxchg(&call->keepalive_at, t, now + MAX_JIFFY_OFFSET);
rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, true, true,
rxrpc_propose_ack_ping_for_keepalive);
set_bit(RXRPC_CALL_EV_PING, &call->events);
}
t = READ_ONCE(call->ping_at);
if (time_after_eq(now, t)) {
trace_rxrpc_timer(call, rxrpc_timer_exp_ping, now);
cmpxchg(&call->ping_at, t, now + MAX_JIFFY_OFFSET);
set_bit(RXRPC_CALL_EV_PING, &call->events);
}
t = READ_ONCE(call->resend_at);
if (time_after_eq(now, t)) {
trace_rxrpc_timer(call, rxrpc_timer_exp_resend, now);
cmpxchg(&call->resend_at, t, now + MAX_JIFFY_OFFSET);
set_bit(RXRPC_CALL_EV_RESEND, &call->events);
}
/* Process events */
if (test_and_clear_bit(RXRPC_CALL_EV_EXPIRED, &call->events)) {
if (test_bit(RXRPC_CALL_RX_HEARD, &call->flags) &&
(int)call->conn->hi_serial - (int)call->rx_serial > 0) {
trace_rxrpc_call_reset(call);
rxrpc_abort_call("EXP", call, 0, RX_USER_ABORT, -ECONNRESET);
} else {
rxrpc_abort_call("EXP", call, 0, RX_USER_ABORT, -ETIME);
}
set_bit(RXRPC_CALL_EV_ABORT, &call->events);
goto recheck_state;
}
send_ack = NULL;
if (test_and_clear_bit(RXRPC_CALL_EV_ACK_LOST, &call->events)) {
call->acks_lost_top = call->tx_top;
rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, true, false,
rxrpc_propose_ack_ping_for_lost_ack);
send_ack = &call->acks_lost_ping;
}
if (test_and_clear_bit(RXRPC_CALL_EV_ACK, &call->events) ||
send_ack) {
if (call->ackr_reason) {
rxrpc_send_ack_packet(call, false, send_ack);
goto recheck_state;
}
}
if (test_and_clear_bit(RXRPC_CALL_EV_PING, &call->events)) {
rxrpc_send_ack_packet(call, true, NULL);
goto recheck_state;
}
if (test_and_clear_bit(RXRPC_CALL_EV_RESEND, &call->events)) {
rxrpc_resend(call, now);
goto recheck_state;
}
/* Make sure the timer is restarted */
next = call->expect_rx_by;
#define set(T) { t = READ_ONCE(T); if (time_before(t, next)) next = t; }
set(call->expect_req_by);
set(call->expect_term_by);
set(call->ack_at);
set(call->ack_lost_at);
set(call->resend_at);
set(call->keepalive_at);
set(call->ping_at);
now = jiffies;
if (time_after_eq(now, next))
goto recheck_state;
rxrpc_reduce_call_timer(call, next, now, rxrpc_timer_restart);
/* other events may have been raised since we started checking */
if (call->events && call->state < RXRPC_CALL_COMPLETE)
goto requeue;
out_put:
rxrpc_put_call(call, rxrpc_call_put);
out:
_leave("");
return;
requeue:
__rxrpc_queue_call(call);
goto out;
}