ICMP messages are ratelimited :

After the blamed commits, the two rate limiters are applied in this order:

1) host wide ratelimit (icmp_global_allow())

2) Per destination ratelimit (inetpeer based)

In order to avoid side-channels attacks, we need to apply the per destination check first.

This patch makes the following change :

1) icmp_global_allow() checks if the host wide limit is reached. But credits are not yet consumed. This is deferred to 3)

2) The per destination limit is checked/updated. This might add a new node in inetpeer tree.

3) icmp_global_consume() consumes tokens if prior operations succeeded.

This means that host wide ratelimit is still effective in keeping inetpeer tree small even under DDOS.

As a bonus, I removed icmp_global.lock as the fast path can use a lock-free operation.

Fixes: c0303efeab73 ("net: reduce cycles spend on ICMP replies that gets rate limited") Fixes: 4cdf507d5452 ("icmp: add a global rate limitation") Reported-by: Keyu Man keyu.man@email.ucr.edu Signed-off-by: Eric Dumazet edumazet@google.com Cc: Jesper Dangaard Brouer hawk@kernel.org Cc: stable@vger.kernel.org --- include/net/ip.h | 2 + net/ipv4/icmp.c | 103 ++++++++++++++++++++++++++--------------------- net/ipv6/icmp.c | 28 ++++++++----- 3 files changed, 76 insertions(+), 57 deletions(-)

diff --git a/include/net/ip.h b/include/net/ip.h index c5606cadb1a552f3e282a5e1e721fd47b07432b2..82248813619e3f21e09d52976accbdc76c7668c2 100644 --- a/include/net/ip.h +++ b/include/net/ip.h @@ -795,6 +795,8 @@ static inline void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb) }

bool icmp_global_allow(void); +void icmp_global_consume(void); + extern int sysctl_icmp_msgs_per_sec; extern int sysctl_icmp_msgs_burst;

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c index b8f56d03fcbb62970a828e20dd9f05fcede2d552..0078e8fb2e86d0552ef85eb5bf5bef947b0f1c3d 100644 --- a/net/ipv4/icmp.c +++ b/net/ipv4/icmp.c @@ -224,57 +224,59 @@ int sysctl_icmp_msgs_per_sec __read_mostly = 1000; int sysctl_icmp_msgs_burst __read_mostly = 50;

static struct { - spinlock_t lock; - u32 credit; + atomic_t credit; u32 stamp; -} icmp_global = { - .lock = __SPIN_LOCK_UNLOCKED(icmp_global.lock), -}; +} icmp_global;

/** * icmp_global_allow - Are we allowed to send one more ICMP message ? * * Uses a token bucket to limit our ICMP messages to ~sysctl_icmp_msgs_per_sec. * Returns false if we reached the limit and can not send another packet. - * Note: called with BH disabled + * Works in tandem with icmp_global_consume(). */ bool icmp_global_allow(void) { - u32 credit, delta, incr = 0, now = (u32)jiffies; - bool rc = false; + u32 delta, now, oldstamp; + int incr, new, old;

- /* Check if token bucket is empty and cannot be refilled - * without taking the spinlock. The READ_ONCE() are paired - * with the following WRITE_ONCE() in this same function. + /* Note: many cpus could find this condition true. + * Then later icmp_global_consume() could consume more credits, + * this is an acceptable race. */ - if (!READ_ONCE(icmp_global.credit)) { - delta = min_t(u32, now - READ_ONCE(icmp_global.stamp), HZ); - if (delta < HZ / 50) - return false; - } + if (atomic_read(&icmp_global.credit) > 0) + return true;

- spin_lock(&icmp_global.lock); - delta = min_t(u32, now - icmp_global.stamp, HZ); - if (delta >= HZ / 50) { - incr = READ_ONCE(sysctl_icmp_msgs_per_sec) * delta / HZ; - if (incr) - WRITE_ONCE(icmp_global.stamp, now); - } - credit = min_t(u32, icmp_global.credit + incr, - READ_ONCE(sysctl_icmp_msgs_burst)); - if (credit) { - /* We want to use a credit of one in average, but need to randomize - * it for security reasons. - */ - credit = max_t(int, credit - get_random_u32_below(3), 0); - rc = true; + now = jiffies; + oldstamp = READ_ONCE(icmp_global.stamp); + delta = min_t(u32, now - oldstamp, HZ); + if (delta < HZ / 50) + return false; + + incr = READ_ONCE(sysctl_icmp_msgs_per_sec) * delta / HZ; + if (!incr) + return false; + + if (cmpxchg(&icmp_global.stamp, oldstamp, now) == oldstamp) { + old = atomic_read(&icmp_global.credit); + do { + new = min(old + incr, READ_ONCE(sysctl_icmp_msgs_burst)); + } while (!atomic_try_cmpxchg(&icmp_global.credit, &old, new)); } - WRITE_ONCE(icmp_global.credit, credit); - spin_unlock(&icmp_global.lock); - return rc; + return true; } EXPORT_SYMBOL(icmp_global_allow);

+void icmp_global_consume(void) +{ + int credits = get_random_u32_below(3); + + /* Note: this might make icmp_global.credit negative. */ + if (credits) + atomic_sub(credits, &icmp_global.credit); +} +EXPORT_SYMBOL(icmp_global_consume); + static bool icmpv4_mask_allow(struct net *net, int type, int code) { if (type > NR_ICMP_TYPES) @@ -291,14 +293,16 @@ static bool icmpv4_mask_allow(struct net *net, int type, int code) return false; }

-static bool icmpv4_global_allow(struct net *net, int type, int code) +static bool icmpv4_global_allow(struct net *net, int type, int code, + bool *apply_ratelimit) { if (icmpv4_mask_allow(net, type, code)) return true;

- if (icmp_global_allow()) + if (icmp_global_allow()) { + *apply_ratelimit = true; return true; - + } __ICMP_INC_STATS(net, ICMP_MIB_RATELIMITGLOBAL); return false; } @@ -308,15 +312,16 @@ static bool icmpv4_global_allow(struct net *net, int type, int code) */

static bool icmpv4_xrlim_allow(struct net *net, struct rtable *rt, - struct flowi4 *fl4, int type, int code) + struct flowi4 *fl4, int type, int code, + bool apply_ratelimit) { struct dst_entry *dst = &rt->dst; struct inet_peer *peer; bool rc = true; int vif;

- if (icmpv4_mask_allow(net, type, code)) - goto out; + if (!apply_ratelimit) + return true;

/* No rate limit on loopback */ if (dst->dev && (dst->dev->flags&IFF_LOOPBACK)) @@ -331,6 +336,8 @@ static bool icmpv4_xrlim_allow(struct net *net, struct rtable *rt, out: if (!rc) __ICMP_INC_STATS(net, ICMP_MIB_RATELIMITHOST); + else + icmp_global_consume(); return rc; }

@@ -402,6 +409,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb) struct ipcm_cookie ipc; struct rtable *rt = skb_rtable(skb); struct net *net = dev_net(rt->dst.dev); + bool apply_ratelimit = false; struct flowi4 fl4; struct sock *sk; struct inet_sock *inet; @@ -413,11 +421,11 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb) if (ip_options_echo(net, &icmp_param->replyopts.opt.opt, skb)) return;

- /* Needed by both icmp_global_allow and icmp_xmit_lock */ + /* Needed by both icmpv4_global_allow and icmp_xmit_lock */ local_bh_disable();

- /* global icmp_msgs_per_sec */ - if (!icmpv4_global_allow(net, type, code)) + /* is global icmp_msgs_per_sec exhausted ? */ + if (!icmpv4_global_allow(net, type, code, &apply_ratelimit)) goto out_bh_enable;

sk = icmp_xmit_lock(net); @@ -450,7 +458,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb) rt = ip_route_output_key(net, &fl4); if (IS_ERR(rt)) goto out_unlock; - if (icmpv4_xrlim_allow(net, rt, &fl4, type, code)) + if (icmpv4_xrlim_allow(net, rt, &fl4, type, code, apply_ratelimit)) icmp_push_reply(sk, icmp_param, &fl4, &ipc, &rt); ip_rt_put(rt); out_unlock: @@ -596,6 +604,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info, int room; struct icmp_bxm icmp_param; struct rtable *rt = skb_rtable(skb_in); + bool apply_ratelimit = false; struct ipcm_cookie ipc; struct flowi4 fl4; __be32 saddr; @@ -677,7 +686,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info, } }

- /* Needed by both icmp_global_allow and icmp_xmit_lock */ + /* Needed by both icmpv4_global_allow and icmp_xmit_lock */ local_bh_disable();

/* Check global sysctl_icmp_msgs_per_sec ratelimit, unless @@ -685,7 +694,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info, * loopback, then peer ratelimit still work (in icmpv4_xrlim_allow) */ if (!(skb_in->dev && (skb_in->dev->flags&IFF_LOOPBACK)) && - !icmpv4_global_allow(net, type, code)) + !icmpv4_global_allow(net, type, code, &apply_ratelimit)) goto out_bh_enable;

sk = icmp_xmit_lock(net); @@ -744,7 +753,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info, goto out_unlock;

/* peer icmp_ratelimit */ - if (!icmpv4_xrlim_allow(net, rt, &fl4, type, code)) + if (!icmpv4_xrlim_allow(net, rt, &fl4, type, code, apply_ratelimit)) goto ende;

/* RFC says return as much as we can without exceeding 576 bytes. */ diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c index 7b31674644efc338ec458d92dfe495480825b0fd..46f70e4a835139ef7d8925c49440865355048193 100644 --- a/net/ipv6/icmp.c +++ b/net/ipv6/icmp.c @@ -175,14 +175,16 @@ static bool icmpv6_mask_allow(struct net *net, int type) return false; }

-static bool icmpv6_global_allow(struct net *net, int type) +static bool icmpv6_global_allow(struct net *net, int type, + bool *apply_ratelimit) { if (icmpv6_mask_allow(net, type)) return true;

- if (icmp_global_allow()) + if (icmp_global_allow()) { + *apply_ratelimit = true; return true; - + } __ICMP_INC_STATS(net, ICMP_MIB_RATELIMITGLOBAL); return false; } @@ -191,13 +193,13 @@ static bool icmpv6_global_allow(struct net *net, int type) * Check the ICMP output rate limit */ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type, - struct flowi6 *fl6) + struct flowi6 *fl6, bool apply_ratelimit) { struct net *net = sock_net(sk); struct dst_entry *dst; bool res = false;

- if (icmpv6_mask_allow(net, type)) + if (!apply_ratelimit) return true;

/* @@ -228,6 +230,8 @@ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type, if (!res) __ICMP6_INC_STATS(net, ip6_dst_idev(dst), ICMP6_MIB_RATELIMITHOST); + else + icmp_global_consume(); dst_release(dst); return res; } @@ -452,6 +456,7 @@ void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info, struct net *net; struct ipv6_pinfo *np; const struct in6_addr *saddr = NULL; + bool apply_ratelimit = false; struct dst_entry *dst; struct icmp6hdr tmp_hdr; struct flowi6 fl6; @@ -533,11 +538,12 @@ void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info, return; }

- /* Needed by both icmp_global_allow and icmpv6_xmit_lock */ + /* Needed by both icmpv6_global_allow and icmpv6_xmit_lock */ local_bh_disable();

/* Check global sysctl_icmp_msgs_per_sec ratelimit */ - if (!(skb->dev->flags & IFF_LOOPBACK) && !icmpv6_global_allow(net, type)) + if (!(skb->dev->flags & IFF_LOOPBACK) && + !icmpv6_global_allow(net, type, &apply_ratelimit)) goto out_bh_enable;

mip6_addr_swap(skb, parm); @@ -575,7 +581,7 @@ void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,

np = inet6_sk(sk);

- if (!icmpv6_xrlim_allow(sk, type, &fl6)) + if (!icmpv6_xrlim_allow(sk, type, &fl6, apply_ratelimit)) goto out;

tmp_hdr.icmp6_type = type; @@ -717,6 +723,7 @@ static enum skb_drop_reason icmpv6_echo_reply(struct sk_buff *skb) struct ipv6_pinfo *np; const struct in6_addr *saddr = NULL; struct icmp6hdr *icmph = icmp6_hdr(skb); + bool apply_ratelimit = false; struct icmp6hdr tmp_hdr; struct flowi6 fl6; struct icmpv6_msg msg; @@ -781,8 +788,9 @@ static enum skb_drop_reason icmpv6_echo_reply(struct sk_buff *skb) goto out;

/* Check the ratelimit */ - if ((!(skb->dev->flags & IFF_LOOPBACK) && !icmpv6_global_allow(net, ICMPV6_ECHO_REPLY)) || - !icmpv6_xrlim_allow(sk, ICMPV6_ECHO_REPLY, &fl6)) + if ((!(skb->dev->flags & IFF_LOOPBACK) && + !icmpv6_global_allow(net, ICMPV6_ECHO_REPLY, &apply_ratelimit)) || + !icmpv6_xrlim_allow(sk, ICMPV6_ECHO_REPLY, &fl6, apply_ratelimit)) goto out_dst_release;

idev = __in6_dev_get(skb->dev);