From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mo4-p02-ob.smtp.rzone.de (mo4-p02-ob.smtp.rzone.de [85.215.255.84]) (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 B8D2F3AD51E for ; Fri, 24 Jul 2026 08:38:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=85.215.255.84 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784882299; cv=pass; b=cgiNuD3Z7psFE6Y8uQsW3qsQEnP61Q+6XvJl/rEeGnxYkENDm/AOsE89fLIDGJccrwBzi+dEbBbR6BCQAxKSNRb0hmGG7ebIwks1vtDNjCj/lrbFoY3dORRufDfk40HwbMHbuvmBI+IlmhIlMJs6FS2HXIZYGHI1VtBBQ8p4eWM= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784882299; c=relaxed/simple; bh=Ikmf1ngB/fGVYj1gu2ECeq275kxS8FxaL1rAdHeEFoo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=AOIIpOFTfFXGOsQzXX3IJI2RTeBQ2+1dAKYk5d04uEBzmvCGjKHr3n0ONR/Kaltz3BTZlYhCJwkjjzwkiSYNNmg4qq1L/WiE1joBabV9nuHTEAX87n1/DXGwDCUL784dkwnsZkoP7iTk2xTHDBsk3wpHPay0DfY9S/FeMl2/5kk= 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=N1b3O7Kx; dkim=permerror (0-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b=1Nogy3oL; arc=pass smtp.client-ip=85.215.255.84 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="N1b3O7Kx"; dkim=permerror (0-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b="1Nogy3oL" ARC-Seal: i=1; a=rsa-sha256; t=1784882287; cv=none; d=strato.com; s=strato-dkim-0002; b=sGMPYM+rERqidhajXZoVL0dPcdCoCB0fdGbQjPC9ze8LyeDHgpsv5zaRC3IPPAPS8V q/GPwUFE1D4SF6fwftIKiOlsnnT9CfgsZKBqOZn9XTMSlffPzFhmifXePHHDukBiK8zH UstHRdWOnH2O6FO63rrrKIvzF5rbU3u9B7zPwifzcakj0PGqn8lhFmf3CdNRkucjnp10 oEDyawRuOANuHv5yyMlVAdg6SHPHnWfFwzGfbWZaHK6Y7SqNRGSi3vSAf1ia87j/CROs ZppUbnjbJ9UYhbklZXvYz4xe7GfjehMJ9Qnq3ba09AtpVhIGc8kcmggjtygnNzLwgonw jgUA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; t=1784882287; 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=NKGY9n0Dgtal55ynXjPcFt9y0bl/A04ngI4Sgi4egXU=; b=W7Pq4j+wo7boTkHz8B++AmsMVnaYwFDyffSt2WvqwGByUU2BtHkLJPlW5N8O/7aAiD Xg6UPCR2+rfBIvpTZ89QsR1YVsibh/F/3tSbTizAk3Tjg55hGOLLP1vPhGfOKGD2obFf 6cypoD7JGq2qWCS8Psw/H9vmW6kwCcmntbKNIMav5bDKsbL+oeV8LLagt/Trve8u3BYL Fodrv7S7rgAkGvrkIOqKi0u/RBWcSMye1R29C4qFCLvi0kPlWL6QVzrgk5ef88YHP3LW R+c5JrZH/TLn/tmiDQf476PUAVllVnGpiwykzxX3/Lej/gmE9B46chMS2EPmPA8glAf5 /XLw== ARC-Authentication-Results: i=1; strato.com; arc=none; dkim=none X-RZG-CLASS-ID: mo02 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; t=1784882287; 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=NKGY9n0Dgtal55ynXjPcFt9y0bl/A04ngI4Sgi4egXU=; b=N1b3O7Kx2cKOiBNLFAAbpj6MwNepjh9juuPXXMqAaGNvVzr4onwQ0AMA4zFnzAtBu6 erM9Bz9bHP3wj6nz+X+QuwJAoz/DNmL880ERiHFam+NqEUzJXT2fgq9b5immqYeoD0zS 36IBW9t89ErRjkZMaugEa2yF76c3ducMs+UuCxvf0+v4hH4Y+ScBJbzvDOKR9o93EV+Y rZUU6VCRgKCKp8JMlMRo3XCsogs6GvvQ7+SB3AVwOB3ODQifju3Ysboa/B01itMQF9a3 jt9LX592OdKJBV0po5TkoJ3b2jVH8U+p9Eo83KcO7NO3IacyrUCTt1hR/cfOzYSliXbB NuNw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; t=1784882287; 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=NKGY9n0Dgtal55ynXjPcFt9y0bl/A04ngI4Sgi4egXU=; b=1Nogy3oLH8fvQDmPbT9Iff+H9XntpHlFrbwuTli36mh04Brdm7H6VkIsHO6cJlCOsa yB5fiyY7hmHOUx5Z6xBw== X-RZG-AUTH: ":P2MHfkW8eP4Mre39l357AZT/I7AY/7nT2yrDxb8mjH4JKvMdQv2tRkI16oOSW1Ti/f4PoH8=" Received: from vivo.lan by smtp.strato.de (RZmta 55.5.6 SBL|AUTH) with ESMTPSA id K5281926O8c6rQ0 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits)) (Client did not present a certificate); Fri, 24 Jul 2026 10:38:06 +0200 (CEST) From: Oliver Hartkopp To: stable@vger.kernel.org Cc: Oliver Hartkopp , Marc Kleine-Budde Subject: [PATCH 1/9] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Date: Fri, 24 Jul 2026 10:37:48 +0200 Message-ID: <20260724083756.12430-2-socketcan@hartkopp.net> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026072036-giving-knee-3a33@gregkh> References: <2026072036-giving-knee-3a33@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 | 36 +++++++++++++++++++++++++++++++++--- 1 file changed, 33 insertions(+), 3 deletions(-) diff --git a/net/can/bcm.c b/net/can/bcm.c index 317cd4c..05ef139 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 */ @@ -1699,7 +1722,7 @@ static int bcm_connect(struct socket *sock, struct sockaddr *uaddr, int len, #if IS_ENABLED(CONFIG_PROC_FS) if (net->can.bcmproc_dir) { /* unique socket address as filename */ - sprintf(bo->procname, "%lu", sock_i_ino(sk)); + sprintf(bo->procname, "%llu", sock_i_ino(sk)); bo->bcm_proc_read = proc_create_net_single(bo->procname, 0644, net->can.bcmproc_dir, bcm_proc_show, sk); @@ -1830,11 +1853,16 @@ 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; } @@ -1848,6 +1876,8 @@ 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); -- 2.43.0