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Commit 4fa48bf3 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: fix tcp_trim_head() 



commit f07d960d (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: default avatarVijay Subramanian <subramanian.vijay@gmail.com>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7d311304

net/ipv4/tcp_output.c

+8 −5
Original line number Diff line number Diff line
@@ -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;