linux-kernel - [PATCH 3.14 08/43] tcp: Fix crash in TCP Fast Open

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Message-Id: <20150417132556.357164854@linuxfoundation.org>
Date:	Fri, 17 Apr 2015 15:28:42 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable <stable@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ben Hutchings <ben@...adent.org.uk>,
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH 3.14 08/43] tcp: Fix crash in TCP Fast Open

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben@...adent.org.uk>

Commit 355a901e6cf1 ("tcp: make connect() mem charging friendly")
changed tcp_send_syn_data() to perform an open-coded copy of the 'syn'
skb rather than using skb_copy_expand().

The open-coded copy does not cover the skb_shared_info::gso_segs
field, so in the new skb it is left set to 0.  When this commit was
backported into stable branches between 3.10.y and 3.16.7-ckty
inclusive, it triggered the BUG() in tcp_transmit_skb().

Since Linux 3.18 the GSO segment count is kept in the
tcp_skb_cb::tcp_gso_segs field and tcp_send_syn_data() does copy the
tcp_skb_cb structure to the new skb, so mainline and newer stable
branches are not affected.

Set skb_shared_info::gso_segs to the correct value of 1.

Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/ipv4/tcp_output.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2933,6 +2933,7 @@ static int tcp_send_syn_data(struct sock
 		goto fallback;
 	syn_data->ip_summed = CHECKSUM_PARTIAL;
 	memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
+	skb_shinfo(syn_data)->gso_segs = 1;
 	if (unlikely(memcpy_fromiovecend(skb_put(syn_data, space),
 					 fo->data->msg_iov, 0, space))) {
 		kfree_skb(syn_data);

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