linux/net/ipv4/tcp_cong.c
Eric Paris a8f80e8ff9 Networking: use CAP_NET_ADMIN when deciding to call request_module
The networking code checks CAP_SYS_MODULE before using request_module() to
try to load a kernel module.  While this seems reasonable it's actually
weakening system security since we have to allow CAP_SYS_MODULE for things
like /sbin/ip and bluetoothd which need to be able to trigger module loads.
CAP_SYS_MODULE actually grants those binaries the ability to directly load
any code into the kernel.  We should instead be protecting modprobe and the
modules on disk, rather than granting random programs the ability to load code
directly into the kernel.  Instead we are going to gate those networking checks
on CAP_NET_ADMIN which still limits them to root but which does not grant
those processes the ability to load arbitrary code into the kernel.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Paul Moore <paul.moore@hp.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: James Morris <jmorris@namei.org>
2009-08-14 11:18:34 +10:00

423 lines
10 KiB
C

/*
* Plugable TCP congestion control support and newReno
* congestion control.
* Based on ideas from I/O scheduler suport and Web100.
*
* Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
*/
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/types.h>
#include <linux/list.h>
#include <net/tcp.h>
int sysctl_tcp_max_ssthresh = 0;
static DEFINE_SPINLOCK(tcp_cong_list_lock);
static LIST_HEAD(tcp_cong_list);
/* Simple linear search, don't expect many entries! */
static struct tcp_congestion_ops *tcp_ca_find(const char *name)
{
struct tcp_congestion_ops *e;
list_for_each_entry_rcu(e, &tcp_cong_list, list) {
if (strcmp(e->name, name) == 0)
return e;
}
return NULL;
}
/*
* Attach new congestion control algorithm to the list
* of available options.
*/
int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
{
int ret = 0;
/* all algorithms must implement ssthresh and cong_avoid ops */
if (!ca->ssthresh || !ca->cong_avoid) {
printk(KERN_ERR "TCP %s does not implement required ops\n",
ca->name);
return -EINVAL;
}
spin_lock(&tcp_cong_list_lock);
if (tcp_ca_find(ca->name)) {
printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
ret = -EEXIST;
} else {
list_add_tail_rcu(&ca->list, &tcp_cong_list);
printk(KERN_INFO "TCP %s registered\n", ca->name);
}
spin_unlock(&tcp_cong_list_lock);
return ret;
}
EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
/*
* Remove congestion control algorithm, called from
* the module's remove function. Module ref counts are used
* to ensure that this can't be done till all sockets using
* that method are closed.
*/
void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
{
spin_lock(&tcp_cong_list_lock);
list_del_rcu(&ca->list);
spin_unlock(&tcp_cong_list_lock);
}
EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
/* Assign choice of congestion control. */
void tcp_init_congestion_control(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_congestion_ops *ca;
/* if no choice made yet assign the current value set as default */
if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
rcu_read_lock();
list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
if (try_module_get(ca->owner)) {
icsk->icsk_ca_ops = ca;
break;
}
/* fallback to next available */
}
rcu_read_unlock();
}
if (icsk->icsk_ca_ops->init)
icsk->icsk_ca_ops->init(sk);
}
/* Manage refcounts on socket close. */
void tcp_cleanup_congestion_control(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
if (icsk->icsk_ca_ops->release)
icsk->icsk_ca_ops->release(sk);
module_put(icsk->icsk_ca_ops->owner);
}
/* Used by sysctl to change default congestion control */
int tcp_set_default_congestion_control(const char *name)
{
struct tcp_congestion_ops *ca;
int ret = -ENOENT;
spin_lock(&tcp_cong_list_lock);
ca = tcp_ca_find(name);
#ifdef CONFIG_MODULES
if (!ca && capable(CAP_NET_ADMIN)) {
spin_unlock(&tcp_cong_list_lock);
request_module("tcp_%s", name);
spin_lock(&tcp_cong_list_lock);
ca = tcp_ca_find(name);
}
#endif
if (ca) {
ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
list_move(&ca->list, &tcp_cong_list);
ret = 0;
}
spin_unlock(&tcp_cong_list_lock);
return ret;
}
/* Set default value from kernel configuration at bootup */
static int __init tcp_congestion_default(void)
{
return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
}
late_initcall(tcp_congestion_default);
/* Build string with list of available congestion control values */
void tcp_get_available_congestion_control(char *buf, size_t maxlen)
{
struct tcp_congestion_ops *ca;
size_t offs = 0;
rcu_read_lock();
list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
offs += snprintf(buf + offs, maxlen - offs,
"%s%s",
offs == 0 ? "" : " ", ca->name);
}
rcu_read_unlock();
}
/* Get current default congestion control */
void tcp_get_default_congestion_control(char *name)
{
struct tcp_congestion_ops *ca;
/* We will always have reno... */
BUG_ON(list_empty(&tcp_cong_list));
rcu_read_lock();
ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
strncpy(name, ca->name, TCP_CA_NAME_MAX);
rcu_read_unlock();
}
/* Built list of non-restricted congestion control values */
void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
{
struct tcp_congestion_ops *ca;
size_t offs = 0;
*buf = '\0';
rcu_read_lock();
list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
continue;
offs += snprintf(buf + offs, maxlen - offs,
"%s%s",
offs == 0 ? "" : " ", ca->name);
}
rcu_read_unlock();
}
/* Change list of non-restricted congestion control */
int tcp_set_allowed_congestion_control(char *val)
{
struct tcp_congestion_ops *ca;
char *clone, *name;
int ret = 0;
clone = kstrdup(val, GFP_USER);
if (!clone)
return -ENOMEM;
spin_lock(&tcp_cong_list_lock);
/* pass 1 check for bad entries */
while ((name = strsep(&clone, " ")) && *name) {
ca = tcp_ca_find(name);
if (!ca) {
ret = -ENOENT;
goto out;
}
}
/* pass 2 clear old values */
list_for_each_entry_rcu(ca, &tcp_cong_list, list)
ca->flags &= ~TCP_CONG_NON_RESTRICTED;
/* pass 3 mark as allowed */
while ((name = strsep(&val, " ")) && *name) {
ca = tcp_ca_find(name);
WARN_ON(!ca);
if (ca)
ca->flags |= TCP_CONG_NON_RESTRICTED;
}
out:
spin_unlock(&tcp_cong_list_lock);
return ret;
}
/* Change congestion control for socket */
int tcp_set_congestion_control(struct sock *sk, const char *name)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_congestion_ops *ca;
int err = 0;
rcu_read_lock();
ca = tcp_ca_find(name);
/* no change asking for existing value */
if (ca == icsk->icsk_ca_ops)
goto out;
#ifdef CONFIG_MODULES
/* not found attempt to autoload module */
if (!ca && capable(CAP_NET_ADMIN)) {
rcu_read_unlock();
request_module("tcp_%s", name);
rcu_read_lock();
ca = tcp_ca_find(name);
}
#endif
if (!ca)
err = -ENOENT;
else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
err = -EPERM;
else if (!try_module_get(ca->owner))
err = -EBUSY;
else {
tcp_cleanup_congestion_control(sk);
icsk->icsk_ca_ops = ca;
if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
icsk->icsk_ca_ops->init(sk);
}
out:
rcu_read_unlock();
return err;
}
/* RFC2861 Check whether we are limited by application or congestion window
* This is the inverse of cwnd check in tcp_tso_should_defer
*/
int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
{
const struct tcp_sock *tp = tcp_sk(sk);
u32 left;
if (in_flight >= tp->snd_cwnd)
return 1;
left = tp->snd_cwnd - in_flight;
if (sk_can_gso(sk) &&
left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
left * tp->mss_cache < sk->sk_gso_max_size)
return 1;
return left <= tcp_max_burst(tp);
}
EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
/*
* Slow start is used when congestion window is less than slow start
* threshold. This version implements the basic RFC2581 version
* and optionally supports:
* RFC3742 Limited Slow Start - growth limited to max_ssthresh
* RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
*/
void tcp_slow_start(struct tcp_sock *tp)
{
int cnt; /* increase in packets */
/* RFC3465: ABC Slow start
* Increase only after a full MSS of bytes is acked
*
* TCP sender SHOULD increase cwnd by the number of
* previously unacknowledged bytes ACKed by each incoming
* acknowledgment, provided the increase is not more than L
*/
if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
return;
if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
else
cnt = tp->snd_cwnd; /* exponential increase */
/* RFC3465: ABC
* We MAY increase by 2 if discovered delayed ack
*/
if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
cnt <<= 1;
tp->bytes_acked = 0;
tp->snd_cwnd_cnt += cnt;
while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
tp->snd_cwnd_cnt -= tp->snd_cwnd;
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
}
}
EXPORT_SYMBOL_GPL(tcp_slow_start);
/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
{
if (tp->snd_cwnd_cnt >= w) {
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
tp->snd_cwnd_cnt = 0;
} else {
tp->snd_cwnd_cnt++;
}
}
EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
/*
* TCP Reno congestion control
* This is special case used for fallback as well.
*/
/* This is Jacobson's slow start and congestion avoidance.
* SIGCOMM '88, p. 328.
*/
void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
{
struct tcp_sock *tp = tcp_sk(sk);
if (!tcp_is_cwnd_limited(sk, in_flight))
return;
/* In "safe" area, increase. */
if (tp->snd_cwnd <= tp->snd_ssthresh)
tcp_slow_start(tp);
/* In dangerous area, increase slowly. */
else if (sysctl_tcp_abc) {
/* RFC3465: Appropriate Byte Count
* increase once for each full cwnd acked
*/
if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
}
} else {
tcp_cong_avoid_ai(tp, tp->snd_cwnd);
}
}
EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
/* Slow start threshold is half the congestion window (min 2) */
u32 tcp_reno_ssthresh(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
return max(tp->snd_cwnd >> 1U, 2U);
}
EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
/* Lower bound on congestion window with halving. */
u32 tcp_reno_min_cwnd(const struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
return tp->snd_ssthresh/2;
}
EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
struct tcp_congestion_ops tcp_reno = {
.flags = TCP_CONG_NON_RESTRICTED,
.name = "reno",
.owner = THIS_MODULE,
.ssthresh = tcp_reno_ssthresh,
.cong_avoid = tcp_reno_cong_avoid,
.min_cwnd = tcp_reno_min_cwnd,
};
/* Initial congestion control used (until SYN)
* really reno under another name so we can tell difference
* during tcp_set_default_congestion_control
*/
struct tcp_congestion_ops tcp_init_congestion_ops = {
.name = "",
.owner = THIS_MODULE,
.ssthresh = tcp_reno_ssthresh,
.cong_avoid = tcp_reno_cong_avoid,
.min_cwnd = tcp_reno_min_cwnd,
};
EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);