Commit 2c51c627 authored Jun 12, 2019 by Eric Dumazet Committed by David S. Miller Jun 14, 2019

net/packet: implement shortcut in tpacket_rcv()



tpacket_rcv() can be hit under DDOS quite hard, since
it will always grab a socket spinlock, to eventually find
there is no room for an additional packet.

Using tcpdump [1] on a busy host can lead to catastrophic consequences,
because of all cpus spinning on a contended spinlock.

This replicates a similar strategy used in packet_rcv()

[1] Also some applications mistakenly use af_packet socket
bound to ETH_P_ALL only to send packets.
Receive queue is never drained and immediately full.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 8e8e2951

net/packet/af_packet.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -2193,6 +2193,12 @@ static int tpacket_rcv(struct sk_buff skb, struct net_device dev,
		if (!res)
		goto drop_n_restore;

		/* If we are flooded, just give up */
		if (__packet_rcv_has_room(po, skb) == ROOM_NONE) {
		atomic_inc(&po->tp_drops);
		goto drop_n_restore;
		}

		if (skb->ip_summed == CHECKSUM_PARTIAL)
		status \|= TP_STATUS_CSUMNOTREADY;
		else if (skb->pkt_type != PACKET_OUTGOING &&