From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Sun, 4 Dec 2011 08:51:08 +0000 (+0000)
Subject: tcp: fix tcp_trim_head()
X-Git-Tag: v3.2.17~94
X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=91bb95f240936feb98f7d540027c78773e4b84cb

tcp: fix tcp_trim_head()

[ Upstream commit 4fa48bf3c75069d636fc8830743c929a062e80dc ]

commit f07d960df3 (tcp: avoid frag allocation for small frames)
breaked assumption in tcp stack that skb is either linear (skb->data_len
== 0), or fully fragged (skb->data_len == skb->len)

tcp_trim_head() made this assumption, we must fix it.

Thanks to Vijay for providing a very detailed explanation.

Reported-by: Vijay Subramanian <subramanian.vijay@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 097e0c72b3fd..7413437efc8d 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1093,6 +1093,13 @@ static void __pskb_trim_head(struct sk_buff *skb, int len)
 {
 	int i, k, eat;
 
+	eat = min_t(int, len, skb_headlen(skb));
+	if (eat) {
+		__skb_pull(skb, eat);
+		len -= eat;
+		if (!len)
+			return;
+	}
 	eat = len;
 	k = 0;
 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
@@ -1124,11 +1131,7 @@ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
 	if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 		return -ENOMEM;
 
-	/* If len == headlen, we avoid __skb_pull to preserve alignment. */
-	if (unlikely(len < skb_headlen(skb)))
-		__skb_pull(skb, len);
-	else
-		__pskb_trim_head(skb, len - skb_headlen(skb));
+	__pskb_trim_head(skb, len);
 
 	TCP_SKB_CB(skb)->seq += len;
 	skb->ip_summed = CHECKSUM_PARTIAL;