[ 074/167] [PATCH 14/26] tcp: fix tcp_trim_head()

Ben Hutchings
2012-05-09T06:06:40Z

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

[ 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>
---
net/ipv4/tcp_output.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 097e0c7..7413437 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;
--
1.7.10