FAILED: patch "[PATCH] mptcp: pm: fix data race in add_addr timer callback" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] mptcp: pm: fix data race in add_addr timer callback" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x a7aad5b69d3bdaec20a3ed9284e184502450c0cd
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026082026-treble-stylized-d851@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a7aad5b69d3bdaec20a3ed9284e184502450c0cd Mon Sep 17 00:00:00 2001
From: Qing Luo <luoqing@kylinos.cn>
Date: Mon, 3 Aug 2026 18:16:36 +0200
Subject: [PATCH] mptcp: pm: fix data race in add_addr timer callback

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>
Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-4-b8f496d71664@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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:

[PATCH 5.15.y 1/4] mptcp: pm: ADD_ADDR rtx: allow ID 0

[Sasha Levin]

From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>

[ Upstream commit 03f324f3f1f7619a47b9c91282cb12775ab0a2f1 ]

ADD_ADDR can be sent for the ID 0, which corresponds to the local
address and port linked to the initial subflow.

Indeed, this address could be removed, and re-added later on, e.g. what
is done in the "delete re-add signal" MPTCP Join selftests. So no reason
to ignore it.

Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260505-net-mptcp-pm-fixes-7-1-rc3-v1-2-fca8091060a4@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: a7aad5b69d3b ("mptcp: pm: fix data race in add_addr timer callback")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/mptcp/pm_netlink.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 87321d545564e..efdea351895d2 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -326,9 +326,6 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 	if (inet_sk_state_load(sk) == TCP_CLOSE)
 		return;
 
-	if (!entry->addr.id)
-		return;
-
 	bh_lock_sock(sk);
 	if (sock_owned_by_user(sk)) {
 		/* Try again later. */
-- 
2.53.0

[PATCH 5.15.y 2/4] mptcp: pm: ADD_ADDR rtx: always decrease sk refcount

[Sasha Levin]

From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>

[ Upstream commit 9634cb35af17019baec21ca648516ce376fa10e6 ]

When an ADD_ADDR is retransmitted, the sk is held in sk_reset_timer().
It should then be released in all cases at the end.

Some (unlikely) checks were returning directly instead of calling
sock_put() to decrease the refcount. Jump to a new 'exit' label to call
__sock_put() (which will become sock_put() in the next commit) to fix
this potential leak.

While at it, drop the '!msk' check which cannot happen because it is
never reset, and explicitly mark the remaining one as "unlikely".

Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260505-net-mptcp-pm-fixes-7-1-rc3-v1-4-fca8091060a4@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: a7aad5b69d3b ("mptcp: pm: fix data race in add_addr timer callback")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/mptcp/pm_netlink.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index efdea351895d2..171d1542f2a4f 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -320,11 +320,8 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 
 	pr_debug("msk=%p\n", msk);
 
-	if (!msk)
-		return;
-
-	if (inet_sk_state_load(sk) == TCP_CLOSE)
-		return;
+	if (unlikely(inet_sk_state_load(sk) == TCP_CLOSE))
+		goto exit;
 
 	bh_lock_sock(sk);
 	if (sock_owned_by_user(sk)) {
@@ -368,6 +365,7 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 
 out:
 	bh_unlock_sock(sk);
+exit:
 	__sock_put(sk);
 }
 
-- 
2.53.0

[PATCH 5.15.y 3/4] mptcp: pm: ADD_ADDR rtx: free sk if last

[Sasha Levin]

From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>

[ Upstream commit b7b9a461569734d33d3259d58d2507adfac107ed ]

When an ADD_ADDR is retransmitted, the sk is held in sk_reset_timer(),
and released at the end.

If at that moment, it was the last reference being held, the sk would
not be freed. sock_put() should then be called instead of __sock_put().

But that's not enough: if it is the last reference, sock_put() will call
sk_free(), which will end up calling sk_stop_timer_sync() on the same
timer, and waiting indefinitely to finish. So it is needed to mark that
the timer is done at the end of the timer handler when it has not been
rescheduled, not to call sk_stop_timer_sync() on "itself".

Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260505-net-mptcp-pm-fixes-7-1-rc3-v1-5-fca8091060a4@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: a7aad5b69d3b ("mptcp: pm: fix data race in add_addr timer callback")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/mptcp/pm_netlink.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 171d1542f2a4f..70170fbbc38d5 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -36,6 +36,7 @@ struct mptcp_pm_add_entry {
 	struct timer_list	add_timer;
 	struct mptcp_sock	*sock;
 	u8			retrans_times;
+	bool			timer_done;
 	struct rcu_head		rcu;
 };
 
@@ -316,22 +317,22 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 	struct mptcp_pm_add_entry *entry = from_timer(entry, timer, add_timer);
 	struct mptcp_sock *msk = entry->sock;
 	struct sock *sk = (struct sock *)msk;
-	unsigned int timeout;
+	unsigned int timeout = 0;
 
 	pr_debug("msk=%p\n", msk);
 
+	bh_lock_sock(sk);
 	if (unlikely(inet_sk_state_load(sk) == TCP_CLOSE))
-		goto exit;
+		goto out;
 
-	bh_lock_sock(sk);
 	if (sock_owned_by_user(sk)) {
 		/* Try again later. */
-		sk_reset_timer(sk, timer, jiffies + HZ / 20);
+		timeout = HZ / 20;
 		goto out;
 	}
 
 	if (mptcp_pm_should_add_signal_addr(msk)) {
-		sk_reset_timer(sk, timer, jiffies + HZ);
+		timeout = HZ;
 		goto out;
 	}
 
@@ -354,9 +355,8 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 		entry->retrans_times++;
 	}
 
-	if (entry->retrans_times < ADD_ADDR_RETRANS_MAX)
-		sk_reset_timer(sk, timer,
-			       jiffies + timeout);
+	if (entry->retrans_times >= ADD_ADDR_RETRANS_MAX)
+		timeout = 0;
 
 	spin_unlock_bh(&msk->pm.lock);
 
@@ -364,9 +364,13 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 		mptcp_pm_subflow_established(msk);
 
 out:
+	if (timeout)
+		sk_reset_timer(sk, timer, jiffies + timeout);
+	else
+		/* if sock_put calls sk_free: avoid waiting for this timer */
+		entry->timer_done = true;
 	bh_unlock_sock(sk);
-exit:
-	__sock_put(sk);
+	sock_put(sk);
 }
 
 struct mptcp_pm_add_entry *
@@ -427,6 +431,7 @@ static bool mptcp_pm_alloc_anno_list(struct mptcp_sock *msk,
 	add_entry->retrans_times = 0;
 
 	timer_setup(&add_entry->add_timer, mptcp_pm_add_timer, 0);
+	add_entry->timer_done = false;
 	timeout = mptcp_get_add_addr_timeout(net);
 	if (timeout)
 		sk_reset_timer(sk, &add_entry->add_timer, jiffies + timeout);
@@ -447,7 +452,8 @@ void mptcp_pm_free_anno_list(struct mptcp_sock *msk)
 	spin_unlock_bh(&msk->pm.lock);
 
 	list_for_each_entry_safe(entry, tmp, &free_list, list) {
-		sk_stop_timer_sync(sk, &entry->add_timer);
+		if (!entry->timer_done)
+			sk_stop_timer_sync(sk, &entry->add_timer);
 		kfree_rcu(entry, rcu);
 	}
 }
-- 
2.53.0

[PATCH 5.15.y 4/4] mptcp: pm: fix data race in add_addr timer callback

[Sasha Levin]

From: Qing Luo <luoqing@kylinos.cn>

[ Upstream commit a7aad5b69d3bdaec20a3ed9284e184502450c0cd ]

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>
Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-4-b8f496d71664@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ applied hunk to mptcp_pm_add_timer() in net/mptcp/pm_netlink.c instead of pm.c, dropping the absent adaptive-timeout shift line ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/mptcp/pm_netlink.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 70170fbbc38d5..e912615e008f3 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -318,6 +318,7 @@ static void mptcp_pm_add_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);
 
@@ -355,12 +356,13 @@ static void mptcp_pm_add_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 = 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