[PATCH net v2 0/8] mptcp: misc fixes for v7.2-rc6

[PATCH net v2 0/8] mptcp: misc fixes for v7.2-rc6

[Matthieu Baerts (NGI0)]

Here are various unrelated fixes:

- Patches 1-3: harden incoming MPTCP suboptions parsing by rejecting
  non-combinable ones. Patch 3 removes unreachable code after patch 2
  added here for consistency, and to reduce comments from AI reviews.
  Fixes for v5.6.

- Patch 4: fix a data race in the ADD_ADDR timer callback. A fix for
  v5.13.

- Patch 5: correctly catch data corruption during the MPTCP join
  selftest by marking tests as failed, instead of only printing a
  warning. A fix for v5.18.

- Patch 6: fix a leak with the userspace ADD_ADDR list in case of race
  condition during teardown. A fix for v5.19.

- Patch 7: deal with MPTFO with a valid token, but no data in the SYN. A
  fix for v6.2.

- Patch 8: reclaim forward-allocated memory in case of error on the
  receive side. A fix for v6.19.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Changes in v2:
- Patches 1, 3, 6: new.
- Patch 2: handle MP_FASTCLOSE & DSS case.
- Patches 2, 4, 7: updated commit message to reply to AI reviews.
- Patch 8: start comment on the same line as the opening /*.
- Note: the title of this series has not been updated: the fixes are
  obviously for the next RC.
- Also, apart from patch 3, the different fixes are independent: in case
  of new issues discovered at review time, valid fixes can already been
  picked up, not to be blocked by unrelated patches.
- Link to v1: https://patch.msgid.link/20260728-net-mptcp-misc-fixes-7-2-rc6-v1-0-f7e2d229159d@kernel.org

---
Gang Yan (1):
      selftests: mptcp: join: mark tests with data corruption as failed

Matthieu Baerts (NGI0) (3):
      mptcp: options: reset DSS fields in case of unexpected size
      mptcp: avoid combining some incoming suboptions
      mptcp: remove MPC && MPJ check

Paolo Abeni (1):
      mptcp: reclaim forward-allocated memory on RX path errors

Qing Luo (1):
      mptcp: pm: fix data race in add_addr timer callback

Shardul Bankar (1):
      mptcp: pm: fix memory leak from alloc-during-teardown race

Wyatt Feng (1):
      mptcp: fastopen: only mark MPTFO subflows with SYN data

 net/mptcp/fastopen.c                            |  7 +--
 net/mptcp/options.c                             | 67 ++++++++++++++++++++++++-
 net/mptcp/pm.c                                  | 19 +++++--
 net/mptcp/pm_userspace.c                        |  4 ++
 net/mptcp/protocol.c                            |  6 +++
 net/mptcp/protocol.h                            |  8 +--
 net/mptcp/subflow.c                             |  5 --
 tools/testing/selftests/net/mptcp/mptcp_join.sh |  4 +-
 8 files changed, 101 insertions(+), 19 deletions(-)
---
base-commit: af39eb111ce6b5eba9c08513b62c4868eb7e7fd5
change-id: 20260728-net-mptcp-misc-fixes-7-2-rc6-22213c66ef75

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

[PATCH net v2 1/8] mptcp: options: reset DSS fields in case of unexpected size

[Matthieu Baerts (NGI0)]

A remote peer could send a malformed DSS with a wrong size, followed by
another DSS or MPC + Data. In this case, the first suboption will be
ignored, but leaving some fields written, which could lead to
inconsistency or access uninitialized data.

Explicitly reset the fields that could have been modified in case of
unexpected size.

Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260728-net-mptcp-misc-fixes-7-2-rc6-v1-0-f7e2d229159d%40kernel.org?part=1
Fixes: 648ef4b88673 ("mptcp: Implement MPTCP receive path")
Cc: stable@vger.kernel.org
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Cc: Davide Caratti <dcaratti@redhat.com>
Cc: Florian Westphal <fw@strlen.de>
Cc: Christoph Paasch <cpaasch@openai.com>
Note: Peter Krystad's email address is no longer valid
v2: New. (Clashiko)
---
 net/mptcp/options.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index c664023d37ba..038eca33c6b1 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -188,8 +188,14 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		 * RFC 8684 Section 3.3.0 checks later in subflow_data_ready
 		 */
 		if (opsize != expected_opsize &&
-		    opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM)
+		    opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM) {
+			mp_opt->dsn64 = 0;
+			mp_opt->use_map = 0;
+			mp_opt->ack64 = 0;
+			mp_opt->use_ack = 0;
+			mp_opt->data_fin = 0;
 			break;
+		}
 
 		mp_opt->suboptions |= OPTION_MPTCP_DSS;
 		if (mp_opt->use_ack) {

-- 
2.53.0

[PATCH net v2 2/8] mptcp: avoid combining some incoming suboptions

[Matthieu Baerts (NGI0)]

Some MPTCP suboptions are mutually exclusive according to the RFC8684,
but also because in different places, the code doesn't expect some
combinations to be present. That's specially true for suboptions that
would be present twice, but with different attributes.

The new restrictions are the same as the ones applied on the output
side, with mptcp_write_options. The same rules can be reused with a
small fix: an MP_FASTCLOSE can be used with a DSS when the sender picks
this option [1], which is not the case on Linux. Here are the rules:

  Which options can be used together?

  X: mutually exclusive
  O: often used together
  C: can be used together in some cases
  P: could be used together but we prefer not to (optimisations)

  | Opt: | MPC  | MPJ  | DSS  | ADD  |  RM  | PRIO | FAIL |  FC  |
  |------|------|------|------|------|------|------|------|------|
  | MPC  |------|------|------|------|------|------|------|------|
  | MPJ  |  X   |------|------|------|------|------|------|------|
  | DSS  |  X   |  X   |------|------|------|------|------|------|
  | ADD  |  X   |  X   |  P   |------|------|------|------|------|
  | RM   |  C   |  C   |  C   |  P   |------|------|------|------|
  | PRIO |  X   |  C   |  C   |  C   |  C   |------|------|------|
  | FAIL |  X   |  X   |  C   |  X   |  X   |  X   |------|------|
  | FC   |  X   |  X   |  P   |  X   |  X   |  X   |  X   |------|
  | RST  |  X   |  X   |  X   |  X   |  X   |  X   |  O   |  O   |
  |------|------|------|------|------|------|------|------|------|

The only difference is with the 'P': another stack could send and
ADD_ADDR with other suboptions (DSS, RM_ADDR), and this should be
allowed.

A few points of attention:

 - In theory, an MP_CAPABLE could be used with a RM_ADDR, but there is
   no reason to add it with a SYN. Note that even with a 4th ACK, it
   doesn't seem to be useful, except when IDs are known in advance via
   another channel. Better not to break that.

 - Now, combining both an MP_CAPABLE and an MP_JOIN will no longer
   result to a reject of the two options, but only the second suboption
   is ignored. That seems OK to do that for this unexpected error. At
   least now all inconsistent combinations are handled the same way.
   This could change later in next. This also means the explicit checks
   for having both MPC + MPJ in subflow.c will now be unreachable.
   That's fine, they will be removed in a follow-up patch.

 - In case of conflicting combinations, the extra suboption(s) is/are
   ignored: having such combinations either means the remote peer is
   buggy, or is evil. The simplest action is then taken in this case:
   stop processing the current suboption.

 - In mp_opt->suboptions, there is also a bit reserved to the checksum,
   which can be used in an MP_CAPABLE and a DSS. Each time a DSS option
   can be used in parallel with another option, the checksum can be set,
   so the verification is combined into a new OPTIONS_MPTCP_DSS macro.

 - An MP_CAPABLE ACK can carry a Data-Level Length, and an optional
   Checksum: they are the same as the ones found in a DSS, because a DSS
   cannot be used in parallel to an MP_CAPABLE. Similarly, even if there
   is room, a DSS cannot be used with an MP_JOIN.

Fixes: eda7acddf808 ("mptcp: Handle MPTCP TCP options")
Cc: stable@vger.kernel.org
Link: https://www.rfc-editor.org/rfc/rfc8684.html#section-3.5-5.1 [1]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Cc: Florian Westphal <fw@strlen.de>
Cc: Davide Caratti <dcaratti@redhat.com>
Cc: Christoph Paasch <cpaasch@openai.com>
Note: Peter Krystad's email address is no longer valid
v2:
 - Handle MP_FASTCLOSE + DSS case. (Clashiko)
 - Updated commit message to reply to (hallucinated) AI reviews.
---
 net/mptcp/options.c  | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 net/mptcp/protocol.h |  1 +
 2 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 038eca33c6b1..1057d500577b 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -50,6 +50,14 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 			}
 		}
 
+		/* Only the MPC + ACK can be used with a RM_ADDR */
+		if (subopt == OPTION_MPTCP_MPC_ACK) {
+			if ((mp_opt->suboptions & ~OPTION_MPTCP_RM_ADDR) != 0)
+				break;
+		} else if (mp_opt->suboptions != 0) {
+			break;
+		}
+
 		/* Cfr RFC 8684 Section 3.3.0:
 		 * If a checksum is present but its use had
 		 * not been negotiated in the MP_CAPABLE handshake, the receiver MUST
@@ -122,6 +130,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_MP_JOIN:
+		/* Can be used with a restricted number of other options */
+		if ((mp_opt->suboptions & ~(OPTION_MPTCP_RM_ADDR |
+					    OPTION_MPTCP_PRIO)) != 0)
+			break;
+
 		if (opsize == TCPOLEN_MPTCP_MPJ_SYN) {
 			mp_opt->suboptions |= OPTION_MPTCP_MPJ_SYN;
 			mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
@@ -153,6 +166,14 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_DSS:
+		/* Can be used with a restricted number of other options */
+		if ((mp_opt->suboptions & ~(OPTION_MPTCP_ADD_ADDR |
+					    OPTION_MPTCP_RM_ADDR |
+					    OPTION_MPTCP_PRIO |
+					    OPTION_MPTCP_FASTCLOSE |
+					    OPTION_MPTCP_FAIL)) != 0)
+			break;
+
 		pr_debug("DSS\n");
 		ptr++;
 
@@ -240,6 +261,12 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_ADD_ADDR:
+		/* Can be used with a restricted number of other options */
+		if ((mp_opt->suboptions & ~(OPTIONS_MPTCP_DSS |
+					    OPTION_MPTCP_RM_ADDR |
+					    OPTION_MPTCP_PRIO)) != 0)
+			break;
+
 		mp_opt->echo = (*ptr++) & MPTCP_ADDR_ECHO;
 		if (!mp_opt->echo) {
 			if (opsize == TCPOLEN_MPTCP_ADD_ADDR ||
@@ -299,6 +326,14 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_RM_ADDR:
+		/* Can be used with a restricted number of other options */
+		if ((mp_opt->suboptions & ~(OPTION_MPTCP_MPC_ACK |
+					    OPTIONS_MPTCP_MPJ |
+					    OPTIONS_MPTCP_DSS |
+					    OPTION_MPTCP_ADD_ADDR |
+					    OPTION_MPTCP_PRIO)) != 0)
+			break;
+
 		if (opsize < TCPOLEN_MPTCP_RM_ADDR_BASE + 1 ||
 		    opsize > TCPOLEN_MPTCP_RM_ADDR_BASE + MPTCP_RM_IDS_MAX)
 			break;
@@ -313,6 +348,13 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_MP_PRIO:
+		/* Can be used with a restricted number of other options */
+		if ((mp_opt->suboptions & ~(OPTIONS_MPTCP_MPJ |
+					    OPTIONS_MPTCP_DSS |
+					    OPTION_MPTCP_ADD_ADDR |
+					    OPTION_MPTCP_RM_ADDR)) != 0)
+			break;
+
 		if (opsize != TCPOLEN_MPTCP_PRIO)
 			break;
 
@@ -322,6 +364,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_MP_FASTCLOSE:
+		/* Can be used with a restricted number of other options */
+		if ((mp_opt->suboptions & ~(OPTIONS_MPTCP_DSS |
+					    OPTION_MPTCP_RST)) != 0)
+			break;
+
 		if (opsize != TCPOLEN_MPTCP_FASTCLOSE)
 			break;
 
@@ -333,6 +380,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_RST:
+		/* Can be used with a restricted number of other options */
+		if ((mp_opt->suboptions & ~(OPTION_MPTCP_FAIL |
+					    OPTION_MPTCP_FASTCLOSE)) != 0)
+			break;
+
 		if (opsize != TCPOLEN_MPTCP_RST)
 			break;
 
@@ -348,6 +400,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 		break;
 
 	case MPTCPOPT_MP_FAIL:
+		/* Can be used with a restricted number of other options */
+		if ((mp_opt->suboptions & ~(OPTIONS_MPTCP_DSS |
+					    OPTION_MPTCP_RST)) != 0)
+			break;
+
 		if (opsize != TCPOLEN_MPTCP_FAIL)
 			break;
 
@@ -1406,7 +1463,7 @@ void mptcp_write_options(struct tcphdr *th, __be32 *ptr, struct tcp_sock *tp,
 	 *  RM   |  C   |  C   |  C   |  P   |------|------|------|------|
 	 *  PRIO |  X   |  C   |  C   |  C   |  C   |------|------|------|
 	 *  FAIL |  X   |  X   |  C   |  X   |  X   |  X   |------|------|
-	 *  FC   |  X   |  X   |  X   |  X   |  X   |  X   |  X   |------|
+	 *  FC   |  X   |  X   |  P   |  X   |  X   |  X   |  X   |------|
 	 *  RST  |  X   |  X   |  X   |  X   |  X   |  X   |  O   |  O   |
 	 * ------|------|------|------|------|------|------|------|------|
 	 *
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 4a2d40cd7b13..c13680d18994 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -37,6 +37,7 @@
 				 OPTION_MPTCP_MPC_ACK)
 #define OPTIONS_MPTCP_MPJ	(OPTION_MPTCP_MPJ_SYN | OPTION_MPTCP_MPJ_SYNACK | \
 				 OPTION_MPTCP_MPJ_ACK)
+#define OPTIONS_MPTCP_DSS	(OPTION_MPTCP_DSS | OPTION_MPTCP_CSUMREQD)
 
 /* MPTCP option subtypes */
 #define MPTCPOPT_MP_CAPABLE	0

-- 
2.53.0

[PATCH net v2 3/8] mptcp: remove MPC && MPJ check

[Matthieu Baerts (NGI0)]

After the parent commit ("mptcp: avoid combining some incoming
suboptions"), the parsing step no longer allow to have both the
MP_CAPABLE and MP_JOIN suboptions set together.

These chunks are now unreachable, these checks can then be removed.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
v2: New. Added here for consistency, and to reduce comments from AI
    reviews. This patch doesn't need to be backported, but it can if it
    helps backporting other patches. (Clashiko)
---
 net/mptcp/subflow.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 8e386899ceb9..e1f20ff8fdb4 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -174,8 +174,6 @@ static int subflow_check_req(struct request_sock *req,
 
 		if (unlikely(listener->pm_listener))
 			return subflow_reset_req_endp(req, skb);
-		if (opt_mp_join)
-			return 0;
 	} else if (opt_mp_join) {
 		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINSYNRX);
 
@@ -277,9 +275,6 @@ int mptcp_subflow_init_cookie_req(struct request_sock *req,
 
 	opt_mp_capable = !!(mp_opt.suboptions & OPTION_MPTCP_MPC_ACK);
 	opt_mp_join = !!(mp_opt.suboptions & OPTION_MPTCP_MPJ_ACK);
-	if (opt_mp_capable && opt_mp_join)
-		return -EINVAL;
-
 	if (opt_mp_capable && listener->request_mptcp) {
 		if (mp_opt.sndr_key == 0)
 			return -EINVAL;

-- 
2.53.0

[PATCH net v2 4/8] mptcp: pm: fix data race in add_addr timer callback

[Matthieu Baerts (NGI0)]

From: Qing Luo <luoqing@kylinos.cn>

The timer callback reads entry->retrans_times outside pm.lock to decide
whether to call mptcp_pm_subflow_established(). Since
mptcp_pm_announced_del_timer() can concurrently set retrans_times =
ADD_ADDR_RETRANS_MAX under pm.lock, a race condition exists.

I discovered this issue while studying the code. AI tools helped me to
verify the issue can potentially happen under race conditions.

Use a local 'retransmit' flag set inside pm.lock to capture whether
retransmission is still possible when the lock is taken. This allows to
call mptcp_pm_subflow_established() accordingly, and not depending on
the situation that can be different when checked outside the pm.lock.

Fixes: 348d5c1dec60 ("mptcp: move to next addr when timeout")
Cc: stable@vger.kernel.org
Signed-off-by: Qing Luo <luoqing@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
v2: clarify commit message to avoid possible confusion. (Clashiko)
---
 net/mptcp/pm.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index 6afd39aea110..c71dcf887683 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -380,6 +380,7 @@ static void mptcp_pm_add_addr_timer(struct timer_list *timer)
 	struct mptcp_sock *msk = entry->sock;
 	struct sock *sk = (struct sock *)msk;
 	unsigned int timeout = 0;
+	bool retransmit;
 
 	pr_debug("msk=%p\n", msk);
 
@@ -412,14 +413,15 @@ static void mptcp_pm_add_addr_timer(struct timer_list *timer)
 		entry->retrans_times++;
 	}
 
-	if (entry->retrans_times < ADD_ADDR_RETRANS_MAX)
+	retransmit = entry->retrans_times < ADD_ADDR_RETRANS_MAX;
+	if (retransmit)
 		timeout <<= entry->retrans_times;
 	else
 		timeout = 0;
 
 	spin_unlock_bh(&msk->pm.lock);
 
-	if (entry->retrans_times == ADD_ADDR_RETRANS_MAX)
+	if (!retransmit)
 		mptcp_pm_subflow_established(msk);
 
 out:

-- 
2.53.0

[PATCH net v2 5/8] selftests: mptcp: join: mark tests with data corruption as failed

[Matthieu Baerts (NGI0)]

From: Gang Yan <yangang@kylinos.cn>

check_transfer() compares the input and output files byte-by-byte using
`cmp -l "$in" "$out" | while read ...`. Because the while-loop body runs
in a subshell (the script sets neither lastpipe nor pipefail), the
fail_test call inside it -- which sets the global ret/last_test_failed --
and the `return 1` both act on the subshell, not on check_transfer().

check_transfer() thus always falls through to `return 0`, and any data
corruption affecting only the payload (leaving the subflow/PM counters
untouched) is silently reported as PASS.

Fixes: 8117dac3e7c3 ("selftests: mptcp: add invert check in check_transfer")
Cc: stable@vger.kernel.org
Assisted-by: Codex:GLM-5.2
Signed-off-by: Gang Yan <yangang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index c0aeffd5cb71..7dc91fac4917 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -584,7 +584,7 @@ check_transfer()
 		mv "$tmpfile" "$out"
 		tmpfile=""
 	fi
-	cmp -l "$in" "$out" | while read -r i a b; do
+	while read -r i a b; do
 		local sum=$((0${a} + 0${b}))
 		if [ $check_invert -eq 0 ] || [ $sum -ne $((0xff)) ]; then
 			fail_test "$what does not match (in, out):"
@@ -595,7 +595,7 @@ check_transfer()
 		else
 			print_info "$what has inverted byte at ${i}"
 		fi
-	done
+	done < <(cmp -l "$in" "$out")
 
 	return 0
 }

-- 
2.53.0

[PATCH net v2 6/8] mptcp: pm: fix memory leak from alloc-during-teardown race

[Matthieu Baerts (NGI0)]

From: Shardul Bankar <shardul.b@mpiricsoftware.com>

mptcp_pm_destroy() empties msk->pm.anno_list and
msk->pm.userspace_pm_local_addr_list under msk->pm.lock during socket
teardown, dropping the lock between the two.

A concurrent userspace PM genl ANNOUNCE on the same msk holds a sock
reference via mptcp_token_get_sock() and, in
mptcp_pm_nl_announce_doit(), calls
mptcp_userspace_pm_append_new_local_addr() and
mptcp_pm_announced_alloc(). Both take msk->pm.lock briefly to add to
their respective lists. Because the genl handler holds a sock reference,
mptcp_pm_destroy() may run on the same msk via mptcp_disconnect(), which
invokes mptcp_destroy_common() without dropping the sock refcount,
before the handler completes.

If the lock acquisitions interleave such that mptcp_pm_destroy() empties
a list first, the later alloc adds its entry to a list head that nothing
else iterates for this msk, and the entry leaks. kmemleak reports both
mptcp_pm_add_addr objects (from mptcp_pm_announced_alloc()) and
mptcp_pm_addr_entry objects (from
mptcp_userspace_pm_append_new_local_addr()) under sustained concurrent
ANNOUNCE + close load against the userspace PM.

Add an MPTCP_PM_DESTROYING bit in msk->pm.status, set by
mptcp_pm_destroy() under pm.lock before the lists are emptied and
checked under pm.lock by the alloc paths. Either the alloc takes pm.lock
first, in which case its entry is on the list when mptcp_pm_destroy()
frees it; or mptcp_pm_destroy() takes pm.lock first, in which case the
later alloc observes the bit and refuses.

Found by an MPTCP protocol-flow harness extending BRF (arXiv:2305.08782).

Fixes: 9ab4807c84a4 ("mptcp: netlink: Add MPTCP_PM_CMD_ANNOUNCE")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Shardul Bankar <shardul.b@mpiricsoftware.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Cc: Kishen Maloor <kishen.maloor@intel.com>
v2: New.
---
 net/mptcp/pm.c           | 13 +++++++++++--
 net/mptcp/pm_userspace.c |  4 ++++
 net/mptcp/protocol.h     |  7 ++++---
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index c71dcf887683..64a1236aabee 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -443,6 +443,9 @@ bool mptcp_pm_announced_alloc(struct mptcp_sock *msk,
 
 	lockdep_assert_held(&msk->pm.lock);
 
+	if (msk->pm.status & BIT(MPTCP_PM_DESTROYING))
+		return false;
+
 	add_entry = mptcp_pm_announced_lookup(msk, addr);
 	if (add_entry) {
 		if (WARN_ON_ONCE(mptcp_pm_is_kernel(msk)))
@@ -1145,10 +1148,16 @@ void mptcp_pm_worker(struct mptcp_sock *msk)
 
 void mptcp_pm_destroy(struct mptcp_sock *msk)
 {
+	spin_lock_bh(&msk->pm.lock);
+	msk->pm.status |= BIT(MPTCP_PM_DESTROYING);
+	spin_unlock_bh(&msk->pm.lock);
+
 	mptcp_pm_free_announced_list(msk);
 
-	if (mptcp_pm_is_userspace(msk))
-		mptcp_userspace_pm_free_local_addr_list(msk);
+	/* Free the userspace local address list unconditionally: the socket
+	 * can be reused (mptcp_disconnect()) and re-selected to a different PM
+	 */
+	mptcp_userspace_pm_free_local_addr_list(msk);
 }
 
 void mptcp_pm_data_reset(struct mptcp_sock *msk)
diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index 945aa5afc2dd..2203cc2d2748 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -54,6 +54,10 @@ static int mptcp_userspace_pm_append_new_local_addr(struct mptcp_sock *msk,
 	bitmap_zero(id_bitmap, MPTCP_PM_MAX_ADDR_ID + 1);
 
 	spin_lock_bh(&msk->pm.lock);
+	if (msk->pm.status & BIT(MPTCP_PM_DESTROYING)) {
+		ret = -EINVAL;
+		goto append_err;
+	}
 	mptcp_for_each_userspace_pm_addr(msk, e) {
 		addr_match = mptcp_addresses_equal(&e->addr, &entry->addr, true);
 		if (addr_match && entry->addr.id == 0 && needs_id)
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index c13680d18994..1b80f2d6ec5a 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -190,9 +190,10 @@ enum mptcp_pm_status {
 	MPTCP_PM_ESTABLISHED,
 	MPTCP_PM_SUBFLOW_ESTABLISHED,
 	MPTCP_PM_ALREADY_ESTABLISHED,	/* persistent status, set after ESTABLISHED event */
-	MPTCP_PM_MPC_ENDPOINT_ACCOUNTED /* persistent status, set after MPC local address is
-					 * accounted int id_avail_bitmap
-					 */
+	MPTCP_PM_MPC_ENDPOINT_ACCOUNTED, /* persistent status, set after MPC local address is
+					  * accounted int id_avail_bitmap
+					  */
+	MPTCP_PM_DESTROYING,		/* To fence out PM list allocs */
 };
 
 enum mptcp_pm_type {

-- 
2.53.0

[PATCH net v2 7/8] mptcp: fastopen: only mark MPTFO subflows with SYN data

[Matthieu Baerts (NGI0)]

From: Wyatt Feng <bronzed_45_vested@icloud.com>

Passive TCP Fast Open accepts a valid-cookie SYN even when it carries
no data. In that case the child socket's receive queue is intentionally
left empty.

mptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking
for queued SYN data. That made data-less TFO SYNs hit a WARN and, if
the warning was non-fatal, left stale MPTFO state behind. The stale
flag could later trigger a state-confusion bug in
check_fully_established().

Only mark the subflow as MPTFO after confirming that an SKB was queued.
Return quietly when the receive queue is empty.

Note that mptcp_subflow_context's is_mptfo field is now not just about
subflows where the TFO was present, but about MPTFO subflow that
consumed SYN data. Only having a valid cookie but not carrying data is
not really "doing TFO".

Fixes: 36b122baf6a8 ("mptcp: add subflow_v(4,6)_send_synack()")
Cc: stable@vger.kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Zhengchuan Liang <zcliangcn@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Wyatt Feng <bronzed_45_vested@icloud.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Cc: Dmytro Shytyi <dmytro@shytyi.net>
Note: a v1 has already been shared alone on the netdev ML:
  https://patch.msgid.link/81f26b8fddd59ebb6cecc417fb138d9ff5214e08.1780458440.git.bronzed_45_vested@icloud.com
v2: update commit message to reply to AI reviews. (Clashiko)
---
 net/mptcp/fastopen.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/fastopen.c b/net/mptcp/fastopen.c
index 082c46c0f50e..f717750906ff 100644
--- a/net/mptcp/fastopen.c
+++ b/net/mptcp/fastopen.c
@@ -24,12 +24,13 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf
 	sk = subflow->conn;
 	tp = tcp_sk(ssk);
 
-	subflow->is_mptfo = 1;
-
+	/* A valid TFO cookie does not guarantee SYN data. */
 	skb = skb_peek(&ssk->sk_receive_queue);
-	if (WARN_ON_ONCE(!skb))
+	if (!skb)
 		return;
 
+	subflow->is_mptfo = 1;
+
 	/* dequeue the skb from sk receive queue */
 	__skb_unlink(skb, &ssk->sk_receive_queue);
 	skb_ext_reset(skb);

-- 
2.53.0

[PATCH net v2 8/8] mptcp: reclaim forward-allocated memory on RX path errors

[Matthieu Baerts (NGI0)]

From: Paolo Abeni <pabeni@redhat.com>

After commit 9db5b3cec4ec ("mptcp: borrow forward memory from subflow"),
errors in the receive path prior to queueing skbs into the receive
queue do not trigger forward-allocated memory reclaiming.

Prevent forward memory from growing unboundedly in pathological drop
scenarios by explicitly reclaiming memory when skbs are dropped.

Fixes: 9db5b3cec4ec ("mptcp: borrow forward memory from subflow")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
v2: Start comment on the same line as the opening /*, like in most
    places in the code. (Clashiko)
---
 net/mptcp/protocol.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index ca644ec53eed..7c8180d8d5ef 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -149,6 +149,12 @@ struct sock *__mptcp_nmpc_sk(struct mptcp_sock *msk)
 
 static void mptcp_drop(struct sock *sk, struct sk_buff *skb)
 {
+	/* The skb forward memory was already transferred to sk by
+	 * mptcp_borrow_fwdmem(), even before setting the destructor.
+	 */
+	if (!skb->destructor)
+		sk_mem_reclaim(sk);
+
 	sk_drops_skbadd(sk, skb);
 	__kfree_skb(skb);
 }

-- 
2.53.0

Re: [PATCH net v2 0/8] mptcp: misc fixes for v7.2-rc6

[Matthieu Baerts]

Hello,

Regarding the "funny" Clashiko's (long) comments [1]:

TL;DR: I think this series can be applied as it is.

On 03/08/2026 18:16, Matthieu Baerts (NGI0) wrote:
> Here are various unrelated fixes:
> 
> - Patches 1-3: harden incoming MPTCP suboptions parsing by rejecting
>   non-combinable ones. Patch 3 removes unreachable code after patch 2
>   added here for consistency, and to reduce comments from AI reviews.
>   Fixes for v5.6.

- Patch 1: indeed, there is another existing issue to fix. This will be
done in a follow-up patch.

- Patch 2:
 - Yes, combining some options is wrong, even if the RFC doesn't
explicitly mention that, and if there is space. As I explained in the
commit message when this happens, it is likely a buggy or bad behaviour
from the other peer, no need to try to get things working in this case.
 - No I'm not going to mention all possible wrong combinations, it is
enough to explain the pattern and give the list of allowed combined options.
 - Also, no need to insist about the same existing issue...

- Patch 3: wow, no comments :-O

> - Patch 4: fix a data race in the ADD_ADDR timer callback. A fix for
>   v5.13.

- An existing issue to fix, this will be done in a follow-up patch.

> - Patch 5: correctly catch data corruption during the MPTCP join
>   selftest by marking tests as failed, instead of only printing a
>   warning. A fix for v5.18.
> 
> - Patch 6: fix a leak with the userspace ADD_ADDR list in case of race
>   condition during teardown. A fix for v5.19.

I don't think the mentioned existing race is possible: I would need a
reproducer. Also, I don't think the commit message needs to be even
longer, and no need to change the error for the userspace daemon: it
will get the notification about the close, and it depends on how the
userspace daemon handle that, possibly in an async way, so no need to
get something better for this race case on the close side.

Also, no need to add a BUILD_BUG_ON(). This can be dealt next time a
flag is added (or on next).

> - Patch 7: deal with MPTFO with a valid token, but no data in the SYN. A
>   fix for v6.2.

Same answer as on v1 (despite the new comment in the commit message):
getting a more precise comment there doesn't have a lot of value: "doing
TFO" means having data in the SYN there. If the comment is modified,
that will certainly cause troubles during the backports.

> - Patch 8: reclaim forward-allocated memory in case of error on the
>   receive side. A fix for v6.19.
Existing issue that will be addressed by the "mptcp: out-of-order queue
pruning" series.

[1]
https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-0-b8f496d71664%40kernel.org

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.

Re: [PATCH net v2 0/8] mptcp: misc fixes for v7.2-rc6

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 03 Aug 2026 18:16:32 +0200 you wrote:
> Here are various unrelated fixes:
> 
> - Patches 1-3: harden incoming MPTCP suboptions parsing by rejecting
>   non-combinable ones. Patch 3 removes unreachable code after patch 2
>   added here for consistency, and to reduce comments from AI reviews.
>   Fixes for v5.6.
> 
> [...]

Here is the summary with links:
  - [net,v2,1/8] mptcp: options: reset DSS fields in case of unexpected size
    https://git.kernel.org/netdev/net/c/35772b4981f3
  - [net,v2,2/8] mptcp: avoid combining some incoming suboptions
    https://git.kernel.org/netdev/net/c/b6ee36152464
  - [net,v2,3/8] mptcp: remove MPC && MPJ check
    https://git.kernel.org/netdev/net/c/900e6d80548e
  - [net,v2,4/8] mptcp: pm: fix data race in add_addr timer callback
    https://git.kernel.org/netdev/net/c/a7aad5b69d3b
  - [net,v2,5/8] selftests: mptcp: join: mark tests with data corruption as failed
    https://git.kernel.org/netdev/net/c/ca318e7bbb77
  - [net,v2,6/8] mptcp: pm: fix memory leak from alloc-during-teardown race
    https://git.kernel.org/netdev/net/c/efc33b5102ff
  - [net,v2,7/8] mptcp: fastopen: only mark MPTFO subflows with SYN data
    https://git.kernel.org/netdev/net/c/e00b63056fb4
  - [net,v2,8/8] mptcp: reclaim forward-allocated memory on RX path errors
    https://git.kernel.org/netdev/net/c/41b49a8b914e

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
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