[PATCH net 0/2] mptcp: 32-bit sequence number improvements

[PATCH net 0/2] mptcp: 32-bit sequence number improvements

[Mat Martineau]

MPTCP-level sequence numbers are 64 bits, but RFC 8684 allows use of
32-bit sequence numbers in the DSS option to save header space. Those
32-bit numbers are the least significant bits of the full 64-bit
sequence number, so the receiver must infer the correct upper 32 bits.

These two patches improve the logic for determining the full 64-bit
sequence numbers when the 32-bit truncated version has wrapped around.

Paolo Abeni (2):
  mptcp: fix bad handling of 32 bit ack wrap-around
  mptcp: fix 32 bit DSN expansion

 net/mptcp/options.c  | 29 +++++++++++++++--------------
 net/mptcp/protocol.h |  8 ++++++++
 net/mptcp/subflow.c  | 17 +----------------
 3 files changed, 24 insertions(+), 30 deletions(-)


base-commit: 9cca0c2d70149160407bda9a9446ce0c29b6e6c6
-- 
2.32.0

[PATCH net 1/2] mptcp: fix bad handling of 32 bit ack wrap-around

[Mat Martineau]

From: Paolo Abeni <pabeni@redhat.com>

When receiving 32 bits DSS ack from the peer, the MPTCP need
to expand them to 64 bits value. The current code is buggy
WRT detecting 32 bits ack wrap-around: when the wrap-around
happens the current unsigned 32 bit ack value is lower than
the previous one.

Additionally check for possible reverse wrap and make the helper
visible, so that we could re-use it for the next patch.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/204
Fixes: cc9d25669866 ("mptcp: update per unacked sequence on pkt reception")
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/options.c  | 29 +++++++++++++++--------------
 net/mptcp/protocol.h |  8 ++++++++
 2 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 9b263f27ce9b..b87e46f515fb 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -896,19 +896,20 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
 	return false;
 }
 
-static u64 expand_ack(u64 old_ack, u64 cur_ack, bool use_64bit)
+u64 __mptcp_expand_seq(u64 old_seq, u64 cur_seq)
 {
-	u32 old_ack32, cur_ack32;
-
-	if (use_64bit)
-		return cur_ack;
-
-	old_ack32 = (u32)old_ack;
-	cur_ack32 = (u32)cur_ack;
-	cur_ack = (old_ack & GENMASK_ULL(63, 32)) + cur_ack32;
-	if (unlikely(before(cur_ack32, old_ack32)))
-		return cur_ack + (1LL << 32);
-	return cur_ack;
+	u32 old_seq32, cur_seq32;
+
+	old_seq32 = (u32)old_seq;
+	cur_seq32 = (u32)cur_seq;
+	cur_seq = (old_seq & GENMASK_ULL(63, 32)) + cur_seq32;
+	if (unlikely(cur_seq32 < old_seq32 && before(old_seq32, cur_seq32)))
+		return cur_seq + (1LL << 32);
+
+	/* reverse wrap could happen, too */
+	if (unlikely(cur_seq32 > old_seq32 && after(old_seq32, cur_seq32)))
+		return cur_seq - (1LL << 32);
+	return cur_seq;
 }
 
 static void ack_update_msk(struct mptcp_sock *msk,
@@ -926,7 +927,7 @@ static void ack_update_msk(struct mptcp_sock *msk,
 	 * more dangerous than missing an ack
 	 */
 	old_snd_una = msk->snd_una;
-	new_snd_una = expand_ack(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
+	new_snd_una = mptcp_expand_seq(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
 
 	/* ACK for data not even sent yet? Ignore. */
 	if (after64(new_snd_una, snd_nxt))
@@ -963,7 +964,7 @@ bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool us
 		return false;
 
 	WRITE_ONCE(msk->rcv_data_fin_seq,
-		   expand_ack(READ_ONCE(msk->ack_seq), data_fin_seq, use_64bit));
+		   mptcp_expand_seq(READ_ONCE(msk->ack_seq), data_fin_seq, use_64bit));
 	WRITE_ONCE(msk->rcv_data_fin, 1);
 
 	return true;
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 385796f0ef19..5d7c44028e47 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -593,6 +593,14 @@ int mptcp_setsockopt(struct sock *sk, int level, int optname,
 int mptcp_getsockopt(struct sock *sk, int level, int optname,
 		     char __user *optval, int __user *option);
 
+u64 __mptcp_expand_seq(u64 old_seq, u64 cur_seq);
+static inline u64 mptcp_expand_seq(u64 old_seq, u64 cur_seq, bool use_64bit)
+{
+	if (use_64bit)
+		return cur_seq;
+
+	return __mptcp_expand_seq(old_seq, cur_seq);
+}
 void __mptcp_check_push(struct sock *sk, struct sock *ssk);
 void __mptcp_data_acked(struct sock *sk);
 void __mptcp_error_report(struct sock *sk);
-- 
2.32.0

[PATCH net 2/2] mptcp: fix 32 bit DSN expansion

[Mat Martineau]

From: Paolo Abeni <pabeni@redhat.com>

The current implementation of 32 bit DSN expansion is buggy.
After the previous patch, we can simply reuse the newly
introduced helper to do the expansion safely.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/120
Fixes: 648ef4b88673 ("mptcp: Implement MPTCP receive path")
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/subflow.c | 17 +----------------
 1 file changed, 1 insertion(+), 16 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index be1de4084196..037fba41e170 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -775,15 +775,6 @@ enum mapping_status {
 	MAPPING_DUMMY
 };
 
-static u64 expand_seq(u64 old_seq, u16 old_data_len, u64 seq)
-{
-	if ((u32)seq == (u32)old_seq)
-		return old_seq;
-
-	/* Assume map covers data not mapped yet. */
-	return seq | ((old_seq + old_data_len + 1) & GENMASK_ULL(63, 32));
-}
-
 static void dbg_bad_map(struct mptcp_subflow_context *subflow, u32 ssn)
 {
 	pr_debug("Bad mapping: ssn=%d map_seq=%d map_data_len=%d",
@@ -907,13 +898,7 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 		data_len--;
 	}
 
-	if (!mpext->dsn64) {
-		map_seq = expand_seq(subflow->map_seq, subflow->map_data_len,
-				     mpext->data_seq);
-		pr_debug("expanded seq=%llu", subflow->map_seq);
-	} else {
-		map_seq = mpext->data_seq;
-	}
+	map_seq = mptcp_expand_seq(READ_ONCE(msk->ack_seq), mpext->data_seq, mpext->dsn64);
 	WRITE_ONCE(mptcp_sk(subflow->conn)->use_64bit_ack, !!mpext->dsn64);
 
 	if (subflow->map_valid) {
-- 
2.32.0

Re: [PATCH net 0/2] mptcp: 32-bit sequence number improvements

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (refs/heads/master):

On Fri, 18 Jun 2021 15:02:19 -0700 you wrote:
> MPTCP-level sequence numbers are 64 bits, but RFC 8684 allows use of
> 32-bit sequence numbers in the DSS option to save header space. Those
> 32-bit numbers are the least significant bits of the full 64-bit
> sequence number, so the receiver must infer the correct upper 32 bits.
> 
> These two patches improve the logic for determining the full 64-bit
> sequence numbers when the 32-bit truncated version has wrapped around.
> 
> [...]

Here is the summary with links:
  - [net,1/2] mptcp: fix bad handling of 32 bit ack wrap-around
    https://git.kernel.org/netdev/net/c/1502328f17ab
  - [net,2/2] mptcp: fix 32 bit DSN expansion
    https://git.kernel.org/netdev/net/c/5957a8901db4

You are awesome, thank you!
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