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.
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]>
> >
> > ...
>
