From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A2B7B41A4EA for ; Mon, 27 Jul 2026 13:39:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785159573; cv=none; b=Ce7nsbS5UO9CZ7+kB2SVF8kah/qMYM0PeuBmH60ha/ZYSJGX5m96i5pV3QKHSUsideIgl//wy2AMB5bRd7z40b4LVl7y2/fhsjB+Fd+zALre1nxIGuvDFqcOpyDBTX7foW1BnnVZQ20+7XtIN7I8JvDtzL19TMJPeJ4nmN4BHmg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785159573; c=relaxed/simple; bh=deJ+CL6XSZlVpoXfwS9TnQ5ZRgL/lrZlV+yQFRfIsg8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VyFteAw0XyzUFSbBiTgiOyCOzFM5ZHkyiG7aTkOJd3zvZkSF33sGxkupv8Cynx6FBH879t6goKhySPz6ZXZvw/25ooSH9nwistfkWRy/nQf0CEUFYidPZoNq3yCEimIOl7H3IWKm378r5ZQu3BN/SEh7MCgjW66+T0cW/2DxMqw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DVS1dykj; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DVS1dykj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B4DF91F00A3E; Mon, 27 Jul 2026 13:39:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785159571; bh=//dP1qkVjIQNb0QPMTU6JCkOaT5rlmsi2vz0B45qckM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=DVS1dykje4bXPl1os8twL/mjd38Wo2nsckOOBW1CuNcYQy9S6zDRKgk9JsRWG4U39 PnQF5/14wazGcRARZJ58GMrW44RVfYUbsK6Iu922fwQYf4S+L0BqzYf6P1Dm6U+rlW hnC288ALNryclOdsnVYZ3Gtuf/ZbsycW8sT3r6ghQ2/37flIyROgYC+J3iqsrS4545 71E/nj+1G0ybkLVpfZpmFqH6F2gheCUh5gnTTgTEm9Abf+5WmiKgmlwJI+mPOWLSEr PjLAvCAHQP2fLNr2xprvGbhpNX6Yti7fk+T7z1q+jVA20sgJXEjvssSnI+DTpol1lT dHklmZLUmfPOA== From: Sasha Levin To: stable@vger.kernel.org Cc: Lee Jones , Feng Xue , Oliver Hartkopp , stable@kernel.org, Marc Kleine-Budde , Sasha Levin Subject: [PATCH 5.10.y 2/2] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Date: Mon, 27 Jul 2026 09:39:28 -0400 Message-ID: <20260727133928.582256-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260727133928.582256-1-sashal@kernel.org> References: <2026072027-showroom-maggot-c452@gregkh> <20260727133928.582256-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Lee Jones [ Upstream commit 68973f9db76144825e4f35dfdc80fb8279eb2d57 ] Commit f1b4e32aca08 ("can: bcm: use call_rcu() instead of costly synchronize_rcu()") replaced synchronize_rcu() in bcm_delete_rx_op() with call_rcu() and introduced the RX_NO_AUTOTIMER flag. However, this flag check was omitted for thrtimer in the packet rx fast-path. During BCM RX operation teardown, a concurrent RCU reader (bcm_rx_handler) can race and re-arm thrtimer via bcm_rx_update_and_send() after call_rcu() has been scheduled. Once the RCU grace period elapses, bcm_op is freed. The subsequently firing thrtimer then dereferences the deallocated op, causing a UAF. Adding flag checks to the rx fast-path (bcm_rx_update_and_send) does not fully close the TOCTOU race and introduces latency for every CAN frame. Conversely, calling hrtimer_cancel() directly inside the RCU callback (softirq context) is fatal as hrtimer_cancel() can sleep, triggering a "scheduling while atomic" panic. Resolve this by deferring the timer cancellation and memory free to a dedicated unbound workqueue (bcm_wq). The RCU callback now queues a work item to bcm_wq, which safely cancels both timers and deallocates memory in sleepable process context. A dedicated workqueue is used to prevent system-wide WQ saturation and is cleanly flushed/destroyed on module unload to avoid rmmod page faults. Since the deferred work can now outlive the calling context by an unbounded amount, also take a reference on op->sk when it is assigned and drop it only once the deferred work has cancelled both timers, so a socket can no longer be freed out from under a still-armed timer whose callback (bcm_send_to_user()) dereferences op->sk. Fixes: f1b4e32aca08 ("can: bcm: use call_rcu() instead of costly synchronize_rcu()") Tested-by: Feng Xue Tested-by: Oliver Hartkopp Signed-off-by: Lee Jones Signed-off-by: Oliver Hartkopp Link: https://patch.msgid.link/20260714-bcm_fixes-v15-1-562f7e3e42da@hartkopp.net Cc: stable@kernel.org Signed-off-by: Marc Kleine-Budde Signed-off-by: Sasha Levin --- net/can/bcm.c | 37 ++++++++++++++++++++++++++++++++++--- 1 file changed, 34 insertions(+), 3 deletions(-) diff --git a/net/can/bcm.c b/net/can/bcm.c index 334a5105a4532c..473e5715da3407 100644 --- a/net/can/bcm.c +++ b/net/can/bcm.c @@ -58,6 +58,7 @@ #include #include #include +#include #include #include #include @@ -89,6 +90,8 @@ MODULE_ALIAS("can-proto-2"); #define BCM_MIN_NAMELEN CAN_REQUIRED_SIZE(struct sockaddr_can, can_ifindex) +static struct workqueue_struct *bcm_wq; + /* * easy access to the first 64 bit of can(fd)_frame payload. cp->data is * 64 bit aligned so the offset has to be multiples of 8 which is ensured @@ -102,6 +105,7 @@ static inline u64 get_u64(const struct canfd_frame *cp, int offset) struct bcm_op { struct list_head list; struct rcu_head rcu; + struct work_struct work; int ifindex; canid_t can_id; u32 flags; @@ -740,9 +744,12 @@ static struct bcm_op *bcm_find_op(struct list_head *ops, return NULL; } -static void bcm_free_op_rcu(struct rcu_head *rcu_head) +static void bcm_free_op_work(struct work_struct *work) { - struct bcm_op *op = container_of(rcu_head, struct bcm_op, rcu); + struct bcm_op *op = container_of(work, struct bcm_op, work); + + hrtimer_cancel(&op->timer); + hrtimer_cancel(&op->thrtimer); if ((op->frames) && (op->frames != &op->sframe)) kfree(op->frames); @@ -750,9 +757,23 @@ static void bcm_free_op_rcu(struct rcu_head *rcu_head) if ((op->last_frames) && (op->last_frames != &op->last_sframe)) kfree(op->last_frames); + /* the last possible access to op->timer/op->thrtimer has now + * happened above via hrtimer_cancel() - op->sk is no longer + * needed by any pending timer callback, so drop our reference + */ + sock_put(op->sk); + kfree(op); } +static void bcm_free_op_rcu(struct rcu_head *rcu_head) +{ + struct bcm_op *op = container_of(rcu_head, struct bcm_op, rcu); + + INIT_WORK(&op->work, bcm_free_op_work); + queue_work(bcm_wq, &op->work); +} + static void bcm_remove_op(struct bcm_op *op) { hrtimer_cancel(&op->timer); @@ -1008,6 +1029,7 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg, /* bcm_can_tx / bcm_tx_timeout_handler needs this */ op->sk = sk; + sock_hold(sk); op->ifindex = ifindex; /* initialize uninitialized (kzalloc) structure */ @@ -1173,6 +1195,7 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg, /* bcm_can_tx / bcm_tx_timeout_handler needs this */ op->sk = sk; + sock_hold(sk); op->ifindex = ifindex; /* ifindex for timeout events w/o previous frame reception */ @@ -1830,11 +1853,15 @@ static int __init bcm_module_init(void) { int err; + bcm_wq = alloc_workqueue("can-bcm-wq", WQ_UNBOUND, 0); + if (!bcm_wq) + return -ENOMEM; + pr_info("can: broadcast manager protocol\n"); err = register_pernet_subsys(&canbcm_pernet_ops); if (err) - return err; + goto register_pernet_failed; err = register_netdevice_notifier(&canbcm_notifier); if (err) @@ -1852,6 +1879,8 @@ static int __init bcm_module_init(void) unregister_netdevice_notifier(&canbcm_notifier); register_notifier_failed: unregister_pernet_subsys(&canbcm_pernet_ops); +register_pernet_failed: + destroy_workqueue(bcm_wq); return err; } @@ -1860,6 +1889,8 @@ static void __exit bcm_module_exit(void) can_proto_unregister(&bcm_can_proto); unregister_netdevice_notifier(&canbcm_notifier); unregister_pernet_subsys(&canbcm_pernet_ops); + rcu_barrier(); + destroy_workqueue(bcm_wq); } module_init(bcm_module_init); -- 2.53.0