Re: [PATCH mptcp-net v4] mptcp: pm: fix userspace PM address ID overflow when all IDs are exhausted

[Matthieu Baerts <matttbe@kernel.org>]

Hi luoqing,

On 07/08/2026 09:41, luoqing wrote:
> From: Qing Luo <luoqing@kylinos.cn>
> 
> When all MPTCP address IDs (1-255) are exhausted in the userspace PM,
> find_next_zero_bit() returns MPTCP_PM_MAX_ADDR_ID + 1 (256). This value
> overflows when stored in the u8 field e->addr.id, resulting in ID 0
> being stored and the entry being incorrectly added to the list.
> 
> ID 0 is reserved for the initial connection in MPTCP, so this overflow
> can cause address conflicts.
> 
> Note: the in-kernel PM already has an 'endpoints == MPTCP_PM_MAX_ADDR_ID'
> check in mptcp_pm_nl_append_new_local_addr() that returns -ERANGE before
> reaching find_next_zero_bit(), preventing this overflow. So this fix only
> addresses the userspace PM path.
> 
> Check the find_next_zero_bit() result against MPTCP_PM_MAX_ADDR_ID and
> return -ENOSPC if all IDs are truly exhausted. Move the ID allocation
> check before the memory allocation so that the error path does not need
> to free the allocated entry.
> 
> Fixes: 4638de5aefe5 ("mptcp: handle local addrs announced by userspace PMs")
> Assisted-by: LLM
> Signed-off-by: Qing Luo <luoqing@kylinos.cn>
> ---
> v4: Move the ID allocation check before the memory allocation so that the error path 
>     does not need to free the allocated entry
Thanks, now in our tree:

New patches for t/upstream-net and t/upstream:
- b57c0c6fddb3: mptcp: pm: fix userspace PM address ID overflow when all
IDs are exhausted
- Results: 4439056e6ccd..d0562342cb80 (export-net)
- Results: e8891858656d..f393de6a43c3 (export)

Tests are now in progress:

- export-net:
https://github.com/multipath-tcp/mptcp_net-next/commit/1f6dc25f039e11595558280af68c916da4e86f71/checks
- export:
https://github.com/multipath-tcp/mptcp_net-next/commit/3601198557ef7a1d08e411ac4ca4aa5e636d4e3e/checks

Cheers,
Matt
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