From: Eric Dumazet <edumazet@google.com>
Date: Fri, 19 Apr 2019 23:02:03 +0000 (-0700)
Subject: tcp: properly reset skb->truesize for tx recycling
X-Git-Tag: Ubuntu-5.4-5.4.0-11.14~2966^2~141
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=d7cc399e1227e74e44f78847d9732a228b46cc91;p=mirror_ubuntu-focal-kernel.git

tcp: properly reset skb->truesize for tx recycling

tcp sendmsg() and sendpage() normally advance skb->data_len
and skb->truesize by the payload added to an skb.

But sendmsg(fd, ..., MSG_ZEROCOPY) has to account for whole pages,
even if a single byte of payload is used in the page.

This means that we can not assume skb->truesize can be adjusted
by skb->data_len. We must instead overwrite its value.

Otherwise skb->truesize is too big and can hit socket sndbuf limit,
especially if the skb is recycled multiple times :/

Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 603e770d59b3..f7567a3698eb 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -868,7 +868,7 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
 	if (likely(!size)) {
 		skb = sk->sk_tx_skb_cache;
 		if (skb && !skb_cloned(skb)) {
-			skb->truesize -= skb->data_len;
+			skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
 			sk->sk_tx_skb_cache = NULL;
 			pskb_trim(skb, 0);
 			INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);