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mptcp: pm: fix extra_subflows underflow on userspace PM subflow creation

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The userspace PM increments extra_subflows after __mptcp_subflow_connect()
succeeds, but __mptcp_subflow_connect() calls mptcp_pm_close_subflow()
on failure to roll back the pre-increment done by the kernel PM's fill_*()
helpers. Because the userspace PM hasn't incremented yet at that point,
this decrement is spurious and causes extra_subflows to underflow.

Fix it by aligning the userspace PM with the kernel PM: increment
extra_subflows before calling __mptcp_subflow_connect(), so the existing
error path in subflow.c correctly rolls it back on failure. Also simplify
the error handling by taking pm.lock only when needed for cleanup.

Fixes: 77e4b94a3d ("mptcp: update userspace pm infos")
Cc: stable@vger.kernel.org
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260602-net-mptcp-misc-fixes-7-1-rc7-v2-5-856831229976@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Tao Cui 2026-06-02 22:14:12 +10:00 committed by Jakub Kicinski
parent da23be77e1
commit 14e9fea30b
1 changed files with 8 additions and 6 deletions
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14
net/mptcp/pm_userspace.c
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@ -408,19 +408,21 @@ int mptcp_pm_nl_subflow_create_doit(struct sk_buff *skb, struct genl_info *info)
local.flags = entry.flags;
local.ifindex = entry.ifindex;
spin_lock_bh(&msk->pm.lock);
msk->pm.extra_subflows++;
spin_unlock_bh(&msk->pm.lock);
lock_sock(sk);
err = __mptcp_subflow_connect(sk, &local, &addr_r);
release_sock(sk);
if (err)
if (err) {
GENL_SET_ERR_MSG_FMT(info, "connect error: %d", err);
spin_lock_bh(&msk->pm.lock);
if (err)
spin_lock_bh(&msk->pm.lock);
mptcp_userspace_pm_delete_local_addr(msk, &entry);
else
msk->pm.extra_subflows++;
spin_unlock_bh(&msk->pm.lock);
spin_unlock_bh(&msk->pm.lock);
}
create_err:
sock_put(sk);