From: Tao Cui <cuitao@kylinos.cn>
Hi,
Following up on issue #629, here is a fix series for the issues
reported against e99c1ca871 ("mptcp: pm: add WARN_ON_ONCE guards
on extra_subflows underflow").
Patch 1 bounds the userspace PM admission at U8_MAX, so the u8 can
no longer be wrapped by a peer establishing more than 255 subflows.
Patch 2 addresses the disconnect() vs MP_JOIN race: as discussed,
the decrement sites now check the msk state first and skip the
accounting when the msk is already in TCP_CLOSE, as the state is set
before mptcp_pm_data_reset() clears the counters, and once the msk
is closed the accounting is not relevant anymore. No new lock is
involved. The guards themselves are downgraded to a clamp with a
rate-limited pr_warn(), as the warn was reachable and turned into a
remotely triggerable panic on panic_on_warn kernels.
Patch 3, from Quanye, applies the same bound to the Netlink subflow
creation path.
Changes since v2:
- Patch 3: label moved inside the if-statement, a note about the
pre-existing unconditional local address deletion in the reused
error path, and the spurious empty line before the SoBs dropped
Changes since v1 [1]:
- Patch 1: re-use "ret" instead of a new variable, drop the
comment, Co-developed-by added for Quanye, who sent the same fix
independently
- issue reference: Link: on patches 1 and 2, Closes: on the last one
- New patch 3 from Quanye for the Netlink path, per the discussion
with Matt [2]
Validated with the virtme CI (mptcp selftests), and with a stress
repro comparing the base kernel and the patched one: on the base
kernel the server accepts 256 MP_JOINs and the counter wraps to 0,
with the patches admission stops at 255 and the leftover imbalance
only shows up as a rate-limited warning.
[1] https://lore.kernel.org/20260831093206.689827-1-cui.tao@linux.dev/
[2] https://lore.kernel.org/all/c8c4f667-5d25-4d94-8627-387d4091c8c4@kernel.org/
Quanye Yang (1):
mptcp: pm: userspace: cap extra_subflows on Netlink subflow creation
Tao Cui (2):
mptcp: pm: bound extra_subflows admission on userspace PM
mptcp: pm: skip extra_subflows accounting on disconnected msk
net/mptcp/pm.c | 17 ++++++++++++++---
net/mptcp/pm_userspace.c | 7 +++++++
net/mptcp/protocol.h | 14 ++++++++++++--
3 files changed, 33 insertions(+), 5 deletions(-)
--
2.43.0