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Date: Wed, 7 Mar 2018 14:59:28 +0200
From: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
To: netdev@...r.kernel.org
Subject: [PATCH net 4/5] tcp: prevent bogus undos when SACK is not enabled
A bogus undo may/will trigger when the loss recovery state is
kept until snd_una is above high_seq. If tcp_any_retrans_done
is zero, retrans_stamp is cleared in this transient state. On
the next ACK, tcp_try_undo_recovery again executes and
tcp_may_undo will always return true because tcp_packet_delayed
has this condition:
return !tp->retrans_stamp || ...
Check for the false fast retransmit transient condition in
tcp_packet_delayed to avoid bogus undos. Since snd_una may have
advanced on this ACK but CA state still remains unchanged,
prior_snd_una needs to be passed instead of tp->snd_una.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
---
net/ipv4/tcp_input.c | 50 ++++++++++++++++++++++++++++++++++----------------
1 file changed, 34 insertions(+), 16 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e20f9ad..b689915 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -98,6 +98,7 @@ int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
#define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */
#define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */
+#define FLAG_PACKET_DELAYED 0x20000 /* 0 rexmits or tstamps reveal delayed pkt */
#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
@@ -2243,10 +2244,19 @@ static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
/* Nothing was retransmitted or returned timestamp is less
* than timestamp of the first retransmission.
*/
-static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
+static inline bool tcp_packet_delayed(const struct sock *sk,
+ const u32 prior_snd_una)
{
- return !tp->retrans_stamp ||
- tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ if (!tp->retrans_stamp) {
+ /* Sender will be in a transient state with cleared
+ * retrans_stamp during false fast retransmit prevention
+ * mechanism
+ */
+ return !tcp_false_fast_retrans_possible(sk, prior_snd_una);
+ }
+ return tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
}
/* Undo procedures. */
@@ -2336,17 +2346,20 @@ static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
tp->rack.advanced = 1; /* Force RACK to re-exam losses */
}
-static inline bool tcp_may_undo(const struct tcp_sock *tp)
+static inline bool tcp_may_undo(const struct sock *sk, const int flag)
{
- return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ return tp->undo_marker &&
+ (!tp->undo_retrans || (flag & FLAG_PACKET_DELAYED));
}
/* People celebrate: "We love our President!" */
-static bool tcp_try_undo_recovery(struct sock *sk)
+static bool tcp_try_undo_recovery(struct sock *sk, const int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
- if (tcp_may_undo(tp)) {
+ if (tcp_may_undo(sk, flag)) {
int mib_idx;
/* Happy end! We did not retransmit anything
@@ -2393,11 +2406,11 @@ static bool tcp_try_undo_dsack(struct sock *sk)
}
/* Undo during loss recovery after partial ACK or using F-RTO. */
-static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
+static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo, const int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
- if (frto_undo || tcp_may_undo(tp)) {
+ if (frto_undo || tcp_may_undo(sk, flag)) {
tcp_undo_cwnd_reduction(sk, true);
DBGUNDO(sk, "partial loss");
@@ -2636,7 +2649,7 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
bool recovered = !before(tp->snd_una, tp->high_seq);
if ((flag & FLAG_SND_UNA_ADVANCED) &&
- tcp_try_undo_loss(sk, false))
+ tcp_try_undo_loss(sk, false, flag))
return;
if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
@@ -2649,7 +2662,7 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
*/
if ((flag & FLAG_ORIG_SACK_ACKED) &&
(tcp_is_sack(tp) || !(flag & FLAG_RETRANS_DATA_ACKED)) &&
- tcp_try_undo_loss(sk, true))
+ tcp_try_undo_loss(sk, true, flag))
return;
if (after(tp->snd_nxt, tp->high_seq)) {
@@ -2672,7 +2685,7 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
if (recovered) {
/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
- tcp_try_undo_recovery(sk);
+ tcp_try_undo_recovery(sk, flag);
return;
}
if (tcp_is_reno(tp)) {
@@ -2688,11 +2701,12 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
}
/* Undo during fast recovery after partial ACK. */
-static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
+static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una,
+ const int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
- if (tp->undo_marker && tcp_packet_delayed(tp)) {
+ if (tp->undo_marker && (flag & FLAG_PACKET_DELAYED)) {
/* Plain luck! Hole if filled with delayed
* packet, rather than with a retransmit. Check reordering.
*/
@@ -2795,13 +2809,17 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
case TCP_CA_Recovery:
if (tcp_is_reno(tp))
tcp_reset_reno_sack(tp);
- if (tcp_try_undo_recovery(sk))
+ if (tcp_try_undo_recovery(sk, flag))
return;
tcp_end_cwnd_reduction(sk);
break;
}
}
+ if (icsk->icsk_ca_state >= TCP_CA_Recovery &&
+ tcp_packet_delayed(sk, prior_snd_una))
+ flag |= FLAG_PACKET_DELAYED;
+
/* E. Process state. */
switch (icsk->icsk_ca_state) {
case TCP_CA_Recovery:
@@ -2809,7 +2827,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
if (tcp_is_reno(tp) && is_dupack)
tcp_add_reno_sack(sk);
} else {
- if (tcp_try_undo_partial(sk, prior_snd_una))
+ if (tcp_try_undo_partial(sk, prior_snd_una, flag))
return;
/* Partial ACK arrived. Force fast retransmit. */
do_lost = tcp_is_reno(tp) ||
--
2.7.4
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