From: Eric Dumazet <eric.dumazet@gmail.com>

BugLink: https://bugs.launchpad.net/bugs/809318

Current socket backlog limit is not enough to really stop DDOS attacks,
because user thread spend many time to process a full backlog each
round, and user might crazy spin on socket lock.

We should add backlog size and receive_queue size (aka rmem_alloc) to
pace writers, and let user run without being slow down too much.

Introduce a sk_rcvqueues_full() helper, to avoid taking socket lock in
stress situations.

Under huge stress from a multiqueue/RPS enabled NIC, a single flow udp
receiver can now process ~200.000 pps (instead of ~100 pps before the
patch) on a 8 core machine.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit c377411f2494a931ff7facdbb3a6839b1266bcf6)

Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
---
include/net/sock.h | 13 +++++++++++--
net/core/sock.c | 5 ++++-
net/ipv4/udp.c | 4 ++++
net/ipv6/udp.c | 8 ++++++++
net/sctp/socket.c | 3 ---
5 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index dcdedf3..2199d35 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -243,7 +243,6 @@ struct sock {
struct sk_buff *head;
struct sk_buff *tail;
int len;
- int limit;
} sk_backlog;
wait_queue_head_t *sk_sleep;
struct dst_entry *sk_dst_cache;
@@ -575,10 +574,20 @@ static inline void __sk_add_backlog(struct sock *sk, struct sk_buff *skb)
skb->next = NULL;
}

+/*
+ * Take into account size of receive queue and backlog queue
+ */
+static inline bool sk_rcvqueues_full(const struct sock *sk, const struct sk_buff *skb)
+{
+ unsigned int qsize = sk->sk_backlog.len + atomic_read(&sk->sk_rmem_alloc);
+
+ return qsize + skb->truesize > sk->sk_rcvbuf;
+}
+
/* The per-socket spinlock must be held here. */
static inline int sk_add_backlog(struct sock *sk, struct sk_buff *skb)
{
- if (sk->sk_backlog.len >= max(sk->sk_backlog.limit, sk->sk_rcvbuf << 1))
+ if (sk_rcvqueues_full(sk, skb))
return -ENOBUFS;

__sk_add_backlog(sk, skb);
diff --git a/net/core/sock.c b/net/core/sock.c
index 5d7e9a2..cb18a38 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -323,6 +323,10 @@ int sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested)

skb->dev = NULL;

+ if (sk_rcvqueues_full(sk, skb)) {
+ atomic_inc(&sk->sk_drops);
+ goto discard_and_relse;
+ }
if (nested)
bh_lock_sock_nested(sk);
else
@@ -1846,7 +1850,6 @@ void sock_init_data(struct socket *sock, struct sock *sk)
sk->sk_allocation = GFP_KERNEL;
sk->sk_rcvbuf = sysctl_rmem_default;
sk->sk_sndbuf = sysctl_wmem_default;
- sk->sk_backlog.limit = sk->sk_rcvbuf << 1;
sk->sk_state = TCP_CLOSE;
sk_set_socket(sk, sock);

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 39fa58b..b9d7815 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1156,6 +1156,10 @@ int udp_queue_rcv_skb(struct sock * sk, struct sk_buff *skb)
goto drop;
}

+
+ if (sk_rcvqueues_full(sk, skb))
+ goto drop;
+
rc = 0;

bh_lock_sock(sk);
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index a224be95..af940b7 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -452,6 +452,10 @@ static void flush_stack(struct sock **stack, unsigned int count,

sk = stack[i];
if (skb1) {
+ if (sk_rcvqueues_full(sk, skb)) {
+ kfree_skb(skb1);
+ goto drop;
+ }
bh_lock_sock(sk);
if (!sock_owned_by_user(sk))
udpv6_queue_rcv_skb(sk, skb1);
@@ -628,6 +632,10 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,

/* deliver */

+ if (sk_rcvqueues_full(sk, skb)) {
+ sock_put(sk);
+ goto discard;
+ }
bh_lock_sock(sk);
if (!sock_owned_by_user(sk))
udpv6_queue_rcv_skb(sk, skb);
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 5ffb288..971890d 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3707,9 +3707,6 @@ SCTP_STATIC int sctp_init_sock(struct sock *sk)
SCTP_DBG_OBJCNT_INC(sock);
percpu_counter_inc(&sctp_sockets_allocated);

- /* Set socket backlog limit. */
- sk->sk_backlog.limit = sysctl_sctp_rmem[1];
-
local_bh_disable();
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
local_bh_enable();
--
1.7.4.1


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