From 60b1af3300724d211bb0b420c1fbe6bf5b87b013 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 24 Jan 2017 14:57:36 -0800 Subject: [PATCH] tcp: reduce skb overhead in selected places tcp_add_backlog() can use skb_condense() helper to get better gains and less SKB_TRUESIZE() magic. This only happens when socket backlog has to be used. Some attacks involve specially crafted out of order tiny TCP packets, clogging the ofo queue of (many) sockets. Then later, expensive collapse happens, trying to copy all these skbs into single ones. This unfortunately does not work if each skb has no neighbor in TCP sequence order. By using skb_condense() if the skb could not be coalesced to a prior one, we defeat these kind of threats, potentially saving 4K per skb (or more, since this is one page fragment). A typical NAPI driver allocates gro packets with GRO_MAX_HEAD bytes in skb->head, meaning the copy done by skb_condense() is limited to about 200 bytes. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 1 + net/ipv4/tcp_ipv4.c | 3 +-- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index bfa165cc455a..3de6eba378ad 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4507,6 +4507,7 @@ add_sack: end: if (skb) { tcp_grow_window(sk, skb); + skb_condense(skb); skb_set_owner_r(skb, sk); } } diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index f7325b25b06e..a90b4540c11e 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1556,8 +1556,7 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb) * It has been noticed pure SACK packets were sometimes dropped * (if cooked by drivers without copybreak feature). */ - if (!skb->data_len) - skb->truesize = SKB_TRUESIZE(skb_end_offset(skb)); + skb_condense(skb); if (unlikely(sk_add_backlog(sk, skb, limit))) { bh_unlock_sock(sk); -- 2.30.2