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mptcp: pm: fix data race in add_addr timer callback

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[ Upstream commit a7aad5b69d ]

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: 348d5c1dec ("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 to mptcp_pm_add_timer() in pm_netlink.c instead of pm.c and collapsed the adaptive backoff branch to `if (!retransmit) timeout = 0;` since the tree lacks exponential ADD_ADDR retransmission timeouts ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Qing Luo
2026-08-27 14:29:47 +02:00
committed by Greg Kroah-Hartman
parent 48b76879f5
commit 13aa13ce3d
1 changed files with 4 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/mptcp/pm_netlink.c
+4 -2
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@@ -297,6 +297,7 @@ 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);
@@ -334,12 +335,13 @@ 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: