[PATCH 3.19 007/177] tcp: make sure skb is not shared before using skb_get()

Greg Kroah-Hartman
2015-03-16T14:11:34Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit ba34e6d9d346fe4e05d7e417b9edf5140772d34c ]

IPv6 can keep a copy of SYN message using skb_get() in
tcp_v6_conn_request() so that caller wont free the skb when calling
kfree_skb() later.

Therefore TCP fast open has to clone the skb it is queuing in
child->sk_receive_queue, as all skbs consumed from receive_queue are
freed using __kfree_skb() (ie assuming skb->users == 1)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Fixes: 5b7ed0892f2af ("tcp: move fastopen functions to tcp_fastopen.c")
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/tcp_fastopen.c | 32 ++++++++++++++++++++++++--------
1 file changed, 24 insertions(+), 8 deletions(-)

--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -134,6 +134,7 @@ static bool tcp_fastopen_create_child(st
struct tcp_sock *tp;
struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
struct sock *child;
+ u32 end_seq;

req->num_retrans = 0;
req->num_timeout = 0;
@@ -185,20 +186,35 @@ static bool tcp_fastopen_create_child(st

/* Queue the data carried in the SYN packet. We need to first
* bump skb's refcnt because the caller will attempt to free it.
+ * Note that IPv6 might also have used skb_get() trick
+ * in tcp_v6_conn_request() to keep this SYN around (treq->pktopts)
+ * So we need to eventually get a clone of the packet,
+ * before inserting it in sk_receive_queue.
*
* XXX (TFO) - we honor a zero-payload TFO request for now,
* (any reason not to?) but no need to queue the skb since
* there is no data. How about SYN+FIN?
*/
- if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1) {
- skb = skb_get(skb);
- skb_dst_drop(skb);
- __skb_pull(skb, tcp_hdr(skb)->doff * 4);
- skb_set_owner_r(skb, child);
- __skb_queue_tail(&child->sk_receive_queue, skb);
- tp->syn_data_acked = 1;
+ end_seq = TCP_SKB_CB(skb)->end_seq;
+ if (end_seq != TCP_SKB_CB(skb)->seq + 1) {
+ struct sk_buff *skb2;
+
+ if (unlikely(skb_shared(skb)))
+ skb2 = skb_clone(skb, GFP_ATOMIC);
+ else
+ skb2 = skb_get(skb);
+
+ if (likely(skb2)) {
+ skb_dst_drop(skb2);
+ __skb_pull(skb2, tcp_hdrlen(skb));
+ skb_set_owner_r(skb2, child);
+ __skb_queue_tail(&child->sk_receive_queue, skb2);
+ tp->syn_data_acked = 1;
+ } else {
+ end_seq = TCP_SKB_CB(skb)->seq + 1;
+ }
}
- tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = end_seq;
sk->sk_data_ready(sk);
bh_unlock_sock(child);
sock_put(child);