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

On Fri, Mar 27, 2026 at 01:46:39PM +0200, Nikolay Aleksandrov wrote:

On 27/03/2026 13:34, Simon Horman wrote:

quoted

On Wed, Mar 25, 2026 at 08:24:38PM -0700, Xiang Mei wrote:

quoted

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.

Also, the PoC can crash a kernel without "oops=panic" with this bug.

quoted

quoted

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.

quoted

Reported-by: Weiming Shi <redacted>
Signed-off-by: Xiang Mei <redacted>

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