tcp: fix fack_count accounting on tcp_shift_skb_data()

v4.15 or since commit 737ff314563 ("tcp: use sequence distance to
detect reordering") had switched from the packet-based FACK tracking
to sequence-based.

v4.14 and older still have the old logic and hence on
tcp_skb_shift_data() needs to retain its original logic and have
@fack_count in sync. In other words, we keep the increment of pcount with
tcp_skb_pcount(skb) to later used that to update fack_count. To make it
more explicit we track the new skb that gets incremented to pcount in
@next_pcount, and we get to avoid the constant invocation of
tcp_skb_pcount(skb) all together.

Orabug: 29890820
Fixes: 1b56e4cb5dec ("tcp: limit payload size of sacked skbs")
Reported-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Reviewed-by: John Haxby <john.haxby@oracle.com>
Reviewed-by: Rao Shoaib <rao.shoaib@oracle.com>>>>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4e0216760cc1cf668a0e48ff1c03b9fe16ef5a6d..b042b3343b8c6a517184628f478dd6aa5aa73d3d 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1402,6 +1402,7 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
        struct tcp_sock *tp = tcp_sk(sk);
        struct sk_buff *prev;
        int mss;
+       int next_pcount;
        int pcount = 0;
        int len;
        int in_sack;
@@ -1515,9 +1516,11 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
                goto out;
 
        len = skb->len;
-       pcount = tcp_skb_pcount(skb);
-       if (tcp_skb_shift(prev, skb, pcount, len))
-               tcp_shifted_skb(sk, skb, state, pcount, len, mss, 0);
+       next_pcount = tcp_skb_pcount(skb);
+       if (tcp_skb_shift(prev, skb, next_pcount, len)) {
+               pcount += next_pcount;
+               tcp_shifted_skb(sk, skb, state, next_pcount, len, mss, 0);
+       }
 out:
        state->fack_count += pcount;
        return prev;