[PATCH] net: mctp: hold route device before source address lookup
From: Yiqi Sun <hidden>
Date: 2026-07-31 02:30:57
Also in:
lkml
Subsystem:
management component transport protocol (mctp), networking [general], the rest · Maintainers:
Jeremy Kerr, Matt Johnston, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
mctp_route_lookup() walks the route table under RCU and may find a direct
route whose route-table reference to rt->dev is being removed concurrently
by NETDEV_UNREGISTER.
Since commit 22cb45afd221 ("net: mctp: perform source address lookups
when we populate our dst"), the direct-route lookup path reads the source
address with mctp_dev_saddr(rt->dev) before mctp_dst_from_route() takes the
dst's own mctp_dev reference. If device teardown wins that race,
mctp_route_remove_dev() can delete the route and mctp_route_release() can
drop the route's mctp_dev reference to zero. mctp_dev_put() frees
mdev->addrs synchronously, while only the mctp_dev body is deferred with
kfree_rcu().
That leaves the lookup side able to read freed mdev->addrs in
mctp_dev_saddr(), or later increment a zero refcount in mctp_dev_hold().
Add a try-hold helper for mctp_dev and use it before reading the source
address from a direct route. mctp_dst_from_route() now consumes that held
reference when it populates dst. If no dst is requested, drop the temporary
reference in mctp_route_lookup(). Do the same when the route cannot be used
for a gateway path without a source address.
Fixes: 22cb45afd221 ("net: mctp: perform source address lookups when we populate our dst")
Signed-off-by: Yiqi Sun <redacted>
---
include/net/mctpdevice.h | 1 +
net/mctp/device.c | 5 +++++
net/mctp/route.c | 28 ++++++++++++++++++++--------
3 files changed, 26 insertions(+), 8 deletions(-)
diff --git a/include/net/mctpdevice.h b/include/net/mctpdevice.h
index 957d9ef924c5..1d052f11127c 100644
--- a/include/net/mctpdevice.h
+++ b/include/net/mctpdevice.h@@ -50,6 +50,7 @@ int mctp_register_netdev(struct net_device *dev, void mctp_unregister_netdev(struct net_device *dev); void mctp_dev_hold(struct mctp_dev *mdev); +bool mctp_dev_try_hold(struct mctp_dev *mdev); void mctp_dev_put(struct mctp_dev *mdev); void mctp_dev_set_key(struct mctp_dev *dev, struct mctp_sk_key *key);
diff --git a/net/mctp/device.c b/net/mctp/device.c
index 2c84df674669..18b192bbfaa7 100644
--- a/net/mctp/device.c
+++ b/net/mctp/device.c@@ -303,6 +303,11 @@ void mctp_dev_hold(struct mctp_dev *mdev) refcount_inc(&mdev->refs); } +bool mctp_dev_try_hold(struct mctp_dev *mdev) +{ + return mdev && refcount_inc_not_zero(&mdev->refs); +} + void mctp_dev_put(struct mctp_dev *mdev) { if (mdev && refcount_dec_and_test(&mdev->refs)) {
diff --git a/net/mctp/route.c b/net/mctp/route.c
index 1f3dccbb7aed..3d0737030917 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c@@ -897,15 +897,16 @@ static mctp_eid_t mctp_dev_saddr(struct mctp_dev *dev) return addr; } -/* must only be called on a direct route, as the final output hop */ +/* must only be called on a direct route, as the final output hop, with a + * reference already held on route->dev. + */ static void mctp_dst_from_route(struct mctp_dst *dst, mctp_eid_t eid, mctp_eid_t saddr, unsigned int mtu, - struct mctp_route *route) + struct mctp_route *route, struct mctp_dev *dev) { - mctp_dev_hold(route->dev); dst->nexthop = eid; - dst->dev = route->dev; - dst->mtu = READ_ONCE(dst->dev->dev->mtu); + dst->dev = dev; + dst->mtu = READ_ONCE(dev->dev->mtu); if (mtu) dst->mtu = min(dst->mtu, mtu); dst->halen = 0;
@@ -998,14 +999,25 @@ int mctp_route_lookup(struct net *net, unsigned int dnet, mtu = mtu ?: rt->mtu; if (rt->dst_type == MCTP_ROUTE_DIRECT) { - mctp_eid_t saddr = mctp_dev_saddr(rt->dev); + struct mctp_dev *dev = rt->dev; + mctp_eid_t saddr; + + if (!mctp_dev_try_hold(dev)) + break; + + saddr = mctp_dev_saddr(dev); /* cannot do gateway-ed routes without a src */ - if (saddr == MCTP_ADDR_NULL && depth != 0) + if (saddr == MCTP_ADDR_NULL && depth != 0) { + mctp_dev_put(dev); break; + } if (dst) - mctp_dst_from_route(dst, daddr, saddr, mtu, rt); + mctp_dst_from_route(dst, daddr, saddr, mtu, rt, + dev); + else + mctp_dev_put(dev); rc = 0; break;
--
2.34.1