[MPTCP] [PATCH mptcp 2/4] options: ignore mptcp-level ack that is ahead of write_seq

[MPTCP] [PATCH mptcp 2/4] options: ignore mptcp-level ack that is ahead of write_seq

[Florian Westphal]

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We should not allow a peer to ack data that we haven't even sent yet,
so test incoming una vs. write_seq.

squashto:  mptcp: update per unacked sequence on pkt reception

Signed-off-by: Florian Westphal <fw(a)strlen.de>
---
 net/mptcp/options.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 1b08e1193991..80dbe7662cea 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -566,12 +566,18 @@ static void update_una(struct mptcp_sock *msk,
 		       struct mptcp_options_received *mp_opt)
 {
 	u64 new_snd_una, snd_una, old_snd_una = atomic64_read(&msk->snd_una);
+	u64 write_seq = READ_ONCE(msk->write_seq);
 
 	/* avoid ack expansion on update conflict, to reduce the risk of
 	 * wrongly expanding to a future ack sequence number, which is way
 	 * more dangerous than missing an ack
 	 */
 	new_snd_una = expand_ack(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
+
+	/* ACK for data not even sent yet? Ignore. */
+	if (after64(new_snd_una, write_seq))
+		new_snd_una = old_snd_una;
+
 	while (after64(new_snd_una, old_snd_una)) {
 		snd_una = old_snd_una;
 		old_snd_una = atomic64_cmpxchg(&msk->snd_una, snd_una,
-- 
2.23.0