Re: [PATCH net] bridge: mrp: reject zero test interval to avoid OOM panic

On 28/03/2026 08:19, Xiang Mei wrote:
> On Fri, Mar 27, 2026 at 01:46:39PM +0200, Nikolay Aleksandrov wrote:
>> On 27/03/2026 13:34, Simon Horman wrote:
>>> On Wed, Mar 25, 2026 at 08:24:38PM -0700, Xiang Mei wrote:
>>>> br_mrp_start_test() and br_mrp_start_in_test() accept the user-supplied
>>>> interval value from netlink without validation. When interval is 0,
>>>> usecs_to_jiffies(0) yields 0, causing the delayed work
>>>> (br_mrp_test_work_expired / br_mrp_in_test_work_expired) to reschedule
>>>> itself with zero delay. This creates a tight loop on system_percpu_wq
>>>> that allocates and transmits MRP test frames at maximum rate, exhausting
>>>> all system memory and causing a kernel panic via OOM deadlock.
>>>
>>> I would suspect the primary outcome of this problem is high CPU consumption
>>> rather than memory exhaustion. Is there a reason to expect that
>>> the transmitted fames can't be consumed as fast as they are created?
>>>
>>
>> +1
>> More so with CAP_NET_ADMIN you can cause all sorts of OOM and high-cpu usage
>> conditions. This is a configuration error and OOM doesn't lead to panic unless
>> instructed to. I don't think this is worth changing at all.
> 
> Thanks for your review. This path is reachable from an unprivileged user
> namespace. The capability check goes through rtnetlink_rcv_msg() ->
> netlink_net_capable() -> netlink_ns_capable(), which checks
> CAP_NET_ADMIN against the network namespace's user_ns, not init_user_ns.
 > An unprivileged user can create a user+net namespace, get CAP_NET_ADMIN> 
within it, set up a bridge with MRP, and trigger the zero-interval loop.
> This is not a privileged misconfiguration scenario.

Technically this is also conditional on configuration. It depends first if users
can create namespaces at all, then on the effective and inheritable caps.

Anyway, as I said in a previous reply, I'm fine either way. Please resubmit
with the fixes tag.

> 
> Also, the PoC can crash a kernel without "oops=panic" with this bug.
> 
>>
>>>>
>>>> The same zero-interval issue applies to br_mrp_start_in_test_parse()
>>>> for interconnect test frames.
>>>>
>>>> Use NLA_POLICY_MIN(NLA_U32, 1) in the nla_policy tables for both
>>>> IFLA_BRIDGE_MRP_START_TEST_INTERVAL and
>>>> IFLA_BRIDGE_MRP_START_IN_TEST_INTERVAL, so zero is rejected at the
>>>> netlink attribute parsing layer before the value ever reaches the
>>>> workqueue scheduling code. This is consistent with how other bridge
>>>> subsystems (br_fdb, br_mst) enforce range constraints on netlink
>>>> attributes.
>>>>
>>>> Fixes: 7ab1748e4ce6 ("bridge: mrp: Extend MRP netlink interface for configuring MRP interconnect")
>>>
>>> I think you also want
>>>
>>> Fixes: 20f6a05ef635 ("bridge: mrp: Rework the MRP netlink interface")
>>>
>>> As highlighted by AI review.
>>>
>>>> Reported-by: Weiming Shi <[email protected]>
>>>> Signed-off-by: Xiang Mei <[email protected]>
>>>
>>> ...
>>