From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mo4-p00-ob.smtp.rzone.de (mo4-p00-ob.smtp.rzone.de [85.215.255.20]) (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 276223806B4 for ; Tue, 28 Jul 2026 16:40:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=85.215.255.20 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785256806; cv=pass; b=Z5QT/x9bm8LuunM6k9pbr44+4oR5f6cwxz2tv8r+51tp+DQm6yYIR1qJ4Xt/Hq/Jo1D26ewFldrYiCtr9ccZJSJhBNK1hWk9KPGust530oM9RFYess+SZsGLD6W85wkynP8Fhmpo+Gsd/JfzjUrQzNe/7Goq0Ln2K8g0J7zJL74= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785256806; c=relaxed/simple; bh=dt+gezqxxyzrYaLABvm1618ph3WI4l5bDxfUqpetC/A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=QDllwlmjqGtuvdfwQpDqGYnZQoXt9h2D3Rs4dKZbPc4pMUPVY9iXmdYiLN9qEpsvsBe2vXWXsa0TR3/G1hmFYY40iFvDNP28dZ/kI/ZgNTb4c6TidlZiB5CzYtkWFijU0Esg+S0veYoLr3cE+yJKNiB3CSN39Nte0mEqJ/rSxm8= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=hartkopp.net; spf=fail smtp.mailfrom=hartkopp.net; dkim=pass (2048-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b=UF7uHKCa; dkim=permerror (0-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b=hCJeYvjT; arc=pass smtp.client-ip=85.215.255.20 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=hartkopp.net Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=hartkopp.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b="UF7uHKCa"; dkim=permerror (0-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b="hCJeYvjT" ARC-Seal: i=1; a=rsa-sha256; t=1785256796; cv=none; d=strato.com; s=strato-dkim-0002; b=s3y9x4f5o9NvmlUsbF0yo4EIuifCYg2G/W6v3MxGYGk9bQ4ePrmqv88AV+Uo2bbOQ+ /pwmmfO3QrUHwgaX5i5lfjy1xyoBb8XJODlgFojpwApa2krynDJzBsjLVbNmfeSyj9oa 2ZlmhcH89vC+Fv7YY1QeFdiDTSTJS6PhxpLQ6fX/HQzzCVsGJyIzUQFp6LBludPL6NqI Mx83ekcPWRSz0YFNiXHlpv9fpUwgV193HDriXIZvdqz6TWt4lCHAz7LpUgc2K00sstEj qycYAs8jJXJLDMv79w0DlmMRJly7ME3inH1vss0ItD2vWPb4OZJdJDsnL/exTbeVsIgo q9Cg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; t=1785256796; s=strato-dkim-0002; d=strato.com; h=References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Cc:Date: From:Subject:Sender; bh=cAhJ+NpdgmmhEB13cZgXgFdvmlgPaZMHercypbU1aSc=; b=FH4ue115Nv4YEvLeGsxOFDXE/ejM6Q1ZmkUhIuzw5uH2i2R9q9rL01wUdstMnDwIVG fC0fe0/bP7MuYbasvP001CcPqHx+C/D0xD/qaYO1Tdt1CfGPRAboDKwvhJhAf1aX2mxd 0X7a2Esx1lDizeY2dL0P8ij2lbHQGsS42ku/4hHyREdqrtu2OoQ9M6AUIT+UWbsezSIB yt6uRQh2yitESov8FE9yI1d2ud0rm70aZAFHDTJlDFYQonq9EPV7DbWYotO5ieB1B7YL 3BrSDoa2O6kW+yzBojnEoUQ454paIZ7uv5qe0PsTRgfoWe4sr7aCTaQls1dyWlWFAJRk fzKw== ARC-Authentication-Results: i=1; strato.com; arc=none; dkim=none X-RZG-CLASS-ID: mo00 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; t=1785256796; s=strato-dkim-0002; d=hartkopp.net; h=References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Cc:Date: From:Subject:Sender; bh=cAhJ+NpdgmmhEB13cZgXgFdvmlgPaZMHercypbU1aSc=; b=UF7uHKCatJ7IU03zsNbR4mpIfHCabxGp18YC30rVMIcYbu/HZKk1BZqW4TMyD+amPB mcog83/lXX0sjZLsSJhoI6e//kVy5Ys8dP2D9m+TCu9lRyz6KIXT5S3HrzeasvdnUYhE 1Ma3He7xxLGUgncBVKeMLAfiCZFHAbeecoPhlNK4go20fUldVZ+9hQkkGiKmGp4yCPZP A/AXJb/279kja8WAjESZn0QHycCh3NhVxu6OuDTtTuFliWSbpDq/mVo/LYfKuBPGfnnW 8XttSW+7009EJ4db44pdGvbZmszPdVcvDpKabLXC8rWES6yF7EHlPwkNTDAQbd0iRz5a Vmmg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; t=1785256796; s=strato-dkim-0003; d=hartkopp.net; h=References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Cc:Date: From:Subject:Sender; bh=cAhJ+NpdgmmhEB13cZgXgFdvmlgPaZMHercypbU1aSc=; b=hCJeYvjTo+uu4RFj+I4ZJJMezzuDMQmsU+57HLS9AM+nGEo3BXBAgHokfmtamslc21 1isoZLNTJLZmfo8jXLAQ== X-RZG-AUTH: ":P2MHfkW8eP4Mre39l357AZT/I7AY/7nT2yrDxb8mjH4JKvMdQv2tRkI16oOSW1Ti/f4PoH8=" Received: from vivo.lan by smtp.strato.de (RZmta 55.5.6 SBL|AUTH) with ESMTPSA id K5281926SGduNDe (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits)) (Client did not present a certificate); Tue, 28 Jul 2026 18:39:56 +0200 (CEST) From: Oliver Hartkopp To: stable@vger.kernel.org Cc: Oliver Hartkopp , Marc Kleine-Budde Subject: [PATCH 5.15.y v2 1/9] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Date: Tue, 28 Jul 2026 18:39:44 +0200 Message-ID: <20260728163944.24110-1-socketcan@hartkopp.net> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026072013-groggily-broker-cca7@gregkh> References: <2026072013-groggily-broker-cca7@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" From: Lee Jones commit 68973f9db76144825e4f35dfdc80fb8279eb2d57 upstream. 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: Oliver Hartkopp --- net/can/bcm.c | 34 ++++++++++++++++++++++++++++++++-- 1 file changed, 32 insertions(+), 2 deletions(-) diff --git a/net/can/bcm.c b/net/can/bcm.c index 317cd4c415ba..ca0f5d0c4e9b 100644 --- a/net/can/bcm.c +++ b/net/can/bcm.c @@ -56,10 +56,11 @@ #include #include #include #include #include +#include #include #include #include /* @@ -87,10 +88,12 @@ MODULE_LICENSE("Dual BSD/GPL"); MODULE_AUTHOR("Oliver Hartkopp "); 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 * by the only callers in bcm_rx_cmp_to_index() bcm_rx_handler(). */ @@ -100,10 +103,11 @@ 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; unsigned long frames_abs, frames_filtered; struct bcm_timeval ival1, ival2; @@ -738,23 +742,40 @@ 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); 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); hrtimer_cancel(&op->thrtimer); @@ -1006,10 +1027,11 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg, /* tx_ops never compare with previous received messages */ op->last_frames = NULL; /* bcm_can_tx / bcm_tx_timeout_handler needs this */ op->sk = sk; + sock_hold(sk); op->ifindex = ifindex; /* initialize uninitialized (kzalloc) structure */ hrtimer_init(&op->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT); @@ -1171,10 +1193,11 @@ 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 */ op->rx_ifindex = ifindex; @@ -1828,15 +1851,20 @@ static struct notifier_block canbcm_notifier = { 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 = can_proto_register(&bcm_can_proto); if (err < 0) { printk(KERN_ERR "can: registration of bcm protocol failed\n"); + destroy_workqueue(bcm_wq); return err; } register_pernet_subsys(&canbcm_pernet_ops); register_netdevice_notifier(&canbcm_notifier); @@ -1846,9 +1874,11 @@ static int __init bcm_module_init(void) 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); module_exit(bcm_module_exit); -- 2.53.0