[PATCH net 0/2] mptcp: fix duplicate data handling

[PATCH net 0/2] mptcp: fix duplicate data handling

[Matthieu Baerts (NGI0)]

In some cases, the subflow-level's copied_seq counter was incorrectly
increased, leading to an unexpected subflow reset.

Patch 1/2 fixes the RCVPRUNED MIB counter that was attached to the wrong
event since its introduction in v5.14, backported to v5.11.

Patch 2/2 fixes the copied_seq counter issues, is present since v5.10.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Paolo Abeni (2):
      mptcp: fix bad RCVPRUNED mib accounting
      mptcp: fix duplicate data handling

 net/mptcp/protocol.c |  8 ++++----
 net/mptcp/subflow.c  | 16 ++++++++++++----
 2 files changed, 16 insertions(+), 8 deletions(-)
---
base-commit: 0bf50cead4c4710d9f704778c32ab8af47ddf070
change-id: 20240731-upstream-net-20240731-mptcp-dup-data-f922353130af

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>

[PATCH net 1/2] mptcp: fix bad RCVPRUNED mib accounting

[Matthieu Baerts (NGI0)]

From: Paolo Abeni <pabeni@redhat.com>

Since its introduction, the mentioned MIB accounted for the wrong
event: wake-up being skipped as not-needed on some edge condition
instead of incoming skb being dropped after landing in the (subflow)
receive queue.

Move the increment in the correct location.

Fixes: ce599c516386 ("mptcp: properly account bulk freed memory")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index a2fc54ed68c0..0d536b183a6c 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -350,8 +350,10 @@ static bool __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
 	skb_orphan(skb);
 
 	/* try to fetch required memory from subflow */
-	if (!mptcp_rmem_schedule(sk, ssk, skb->truesize))
+	if (!mptcp_rmem_schedule(sk, ssk, skb->truesize)) {
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RCVPRUNED);
 		goto drop;
+	}
 
 	has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
 
@@ -844,10 +846,8 @@ void mptcp_data_ready(struct sock *sk, struct sock *ssk)
 		sk_rbuf = ssk_rbuf;
 
 	/* over limit? can't append more skbs to msk, Also, no need to wake-up*/
-	if (__mptcp_rmem(sk) > sk_rbuf) {
-		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RCVPRUNED);
+	if (__mptcp_rmem(sk) > sk_rbuf)
 		return;
-	}
 
 	/* Wake-up the reader only for in-sequence data */
 	mptcp_data_lock(sk);

-- 
2.45.2

[PATCH net 2/2] mptcp: fix duplicate data handling

[Matthieu Baerts (NGI0)]

From: Paolo Abeni <pabeni@redhat.com>

When a subflow receives and discards duplicate data, the mptcp
stack assumes that the consumed offset inside the current skb is
zero.

With multiple subflows receiving data simultaneously such assertion
does not held true. As a result the subflow-level copied_seq will
be incorrectly increased and later on the same subflow will observe
a bad mapping, leading to subflow reset.

Address the issue taking into account the skb consumed offset in
mptcp_subflow_discard_data().

Fixes: 04e4cd4f7ca4 ("mptcp: cleanup mptcp_subflow_discard_data()")
Cc: stable@vger.kernel.org
Link: https://github.com/multipath-tcp/mptcp_net-next/issues/501
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/subflow.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 0e4b5bfbeaa1..a21c712350c3 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1230,14 +1230,22 @@ static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
 	bool fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
-	u32 incr;
+	struct tcp_sock *tp = tcp_sk(ssk);
+	u32 offset, incr, avail_len;
 
-	incr = limit >= skb->len ? skb->len + fin : limit;
+	offset = tp->copied_seq - TCP_SKB_CB(skb)->seq;
+	if (WARN_ON_ONCE(offset > skb->len))
+		goto out;
 
-	pr_debug("discarding=%d len=%d seq=%d", incr, skb->len,
-		 subflow->map_subflow_seq);
+	avail_len = skb->len - offset;
+	incr = limit >= avail_len ? avail_len + fin : limit;
+
+	pr_debug("discarding=%d len=%d offset=%d seq=%d", incr, skb->len,
+		 offset, subflow->map_subflow_seq);
 	MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DUPDATA);
 	tcp_sk(ssk)->copied_seq += incr;
+
+out:
 	if (!before(tcp_sk(ssk)->copied_seq, TCP_SKB_CB(skb)->end_seq))
 		sk_eat_skb(ssk, skb);
 	if (mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len)

-- 
2.45.2

Re: [PATCH net 0/2] mptcp: fix duplicate data handling

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Wed, 31 Jul 2024 12:10:13 +0200 you wrote:
> In some cases, the subflow-level's copied_seq counter was incorrectly
> increased, leading to an unexpected subflow reset.
> 
> Patch 1/2 fixes the RCVPRUNED MIB counter that was attached to the wrong
> event since its introduction in v5.14, backported to v5.11.
> 
> Patch 2/2 fixes the copied_seq counter issues, is present since v5.10.
> 
> [...]

Here is the summary with links:
  - [net,1/2] mptcp: fix bad RCVPRUNED mib accounting
    https://git.kernel.org/netdev/net/c/0a567c2a1003
  - [net,2/2] mptcp: fix duplicate data handling
    https://git.kernel.org/netdev/net/c/68cc924729ff

You are awesome, thank you!
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