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Thu, 30 Jul 2026 19:30:56 -0700 (PDT) Received: from localhost.localdomain ([189.1.242.96]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d047abbf6csm416545ad.39.2026.07.30.19.30.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jul 2026 19:30:56 -0700 (PDT) From: Yiqi Sun To: jk@codeconstruct.com.au, matt@codeconstruct.com.au Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Yiqi Sun Subject: [PATCH] net: mctp: hold route device before source address lookup Date: Fri, 31 Jul 2026 10:29:26 +0800 Message-Id: <20260731022926.913865-1-sunyiqixm@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 pop= ulate our dst") Signed-off-by: Yiqi Sun --- 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); =20 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); =20 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); } =20 +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; } =20 -/* 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 =3D eid; - dst->dev =3D route->dev; - dst->mtu =3D READ_ONCE(dst->dev->dev->mtu); + dst->dev =3D dev; + dst->mtu =3D READ_ONCE(dev->dev->mtu); if (mtu) dst->mtu =3D min(dst->mtu, mtu); dst->halen =3D 0; @@ -998,14 +999,25 @@ int mctp_route_lookup(struct net *net, unsigned int d= net, mtu =3D mtu ?: rt->mtu; =20 if (rt->dst_type =3D=3D MCTP_ROUTE_DIRECT) { - mctp_eid_t saddr =3D mctp_dev_saddr(rt->dev); + struct mctp_dev *dev =3D rt->dev; + mctp_eid_t saddr; + + if (!mctp_dev_try_hold(dev)) + break; + + saddr =3D mctp_dev_saddr(dev); =20 /* cannot do gateway-ed routes without a src */ - if (saddr =3D=3D MCTP_ADDR_NULL && depth !=3D 0) + if (saddr =3D=3D MCTP_ADDR_NULL && depth !=3D 0) { + mctp_dev_put(dev); break; + } =20 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 =3D 0; break; =20 --=20 2.34.1