* [PATCH v9 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:34 ` sashiko-bot
2026-07-09 8:16 ` [PATCH v9 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
` (8 subsequent siblings)
9 siblings, 1 reply; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde, Lee Jones, Feng Xue
From: Lee Jones <lee@kernel.org>
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 <feng.xue@outlook.com>
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
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 a4bef2c48a55..bdf53241bd7b 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -56,10 +56,11 @@
#include <linux/can.h>
#include <linux/can/core.h>
#include <linux/can/skb.h>
#include <linux/can/bcm.h>
#include <linux/slab.h>
+#include <linux/workqueue.h>
#include <linux/spinlock.h>
#include <net/can.h>
#include <net/sock.h>
#include <net/net_namespace.h>
@@ -90,10 +91,12 @@ MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Oliver Hartkopp <oliver.hartkopp@volkswagen.de>");
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().
*/
@@ -103,10 +106,11 @@ 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;
@@ -791,23 +795,40 @@ 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);
@@ -1058,10 +1079,11 @@ 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_setup(&op->timer, bcm_tx_timeout_handler, CLOCK_MONOTONIC,
HRTIMER_MODE_REL_SOFT);
@@ -1219,10 +1241,11 @@ 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;
@@ -1837,15 +1860,19 @@ 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 = register_pernet_subsys(&canbcm_pernet_ops);
if (err)
- return err;
+ goto register_pernet_failed;
err = register_netdevice_notifier(&canbcm_notifier);
if (err)
goto register_notifier_failed;
@@ -1859,17 +1886,21 @@ static int __init bcm_module_init(void)
register_proto_failed:
unregister_netdevice_notifier(&canbcm_notifier);
register_notifier_failed:
unregister_pernet_subsys(&canbcm_pernet_ops);
+register_pernet_failed:
+ destroy_workqueue(bcm_wq);
return err;
}
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
^ permalink raw reply related [flat|nested] 16+ messages in thread* Re: [PATCH v9 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
2026-07-09 8:16 ` [PATCH v9 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:34 ` sashiko-bot
0 siblings, 0 replies; 16+ messages in thread
From: sashiko-bot @ 2026-07-09 8:34 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Oliver Hartkopp, Vincent Mailhol, Oleksij Rempel,
Marc Kleine-Budde, linux-can
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Module exit triggers a kmem_cache_destroy warning because the protocol slab cache is destroyed before the deferred workqueue frees the remaining sockets.
--
--- Patch [1]: [PATCH v9 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF ---
commit d847f243125a944d43b2a6970166b528eea27549
Author: Lee Jones <lee@kernel.org>
can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
This commit resolves a use-after-free condition in the broadcast manager
rx operation teardown. It moves the timer cancellation and memory deallocation
to a dedicated unbound workqueue, and ensures the socket reference is held
until the deferred work executes safely in process context.
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index a4bef2c48a559..bdf53241bd7b3 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
[ ... ]
> @@ -1869,6 +1898,8 @@ 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);
> }
[Severity: High]
Will this sequence trigger a kmem_cache_destroy warning on module unload?
Since bcm_module_exit() calls can_proto_unregister() before
destroy_workqueue(), the protocol slab cache is destroyed while deferred
work items that release sockets back to the cache might still be pending in
bcm_wq.
Should destroy_workqueue() be called before can_proto_unregister() to
ensure all pending socket frees are completed prior to the protocol slab
cache destruction?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v9-0-6eebb78ccfb2@hartkopp.net?part=1
^ permalink raw reply [flat|nested] 16+ messages in thread
* [PATCH v9 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
2026-07-09 8:16 ` [PATCH v9 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:36 ` sashiko-bot
2026-07-09 8:16 ` [PATCH v9 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
` (7 subsequent siblings)
9 siblings, 1 reply; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde, Ginger
From: Oliver Hartkopp <socketcan@hartkopp.net>
bcm_sendmsg() reads bo->ifindex and checks bo->bound before taking
lock_sock(), while bcm_notify(), bcm_connect() and bcm_release() all
mutate both fields under that same lock. Because the lockless reads
and the locked writes are unordered with respect to each other, a
racing bcm_notify() (device unregister) or bcm_connect() (concurrent
bind on another thread sharing the socket) can make bcm_sendmsg()
observe an inconsistent combination, e.g. a stale bound=1 together
with the now-cleared ifindex=0, silently turning a socket bound to a
specific CAN interface into one that also matches "any" interface.
Keep the lockless bo->bound check purely as a fast-path reject, and
move the ifindex read (and a bo->bound re-check) into the locked
section, where every writer already serializes. This removes the
possibility of observing the two fields torn against each other,
rather than trying to fix it with more READ_ONCE()/WRITE_ONCE() pairs
on two independently updated fields. Annotate the now-purely-lockless
bo->bound accesses consistently across all its write sites.
Also fix bcm_rx_setup() silently returning success when the target
device disappears concurrently instead of reporting -ENODEV, so a
broken RX op is no longer left registered as if it had succeeded.
Reported-by: Ginger <ginger.jzllee@gmail.com>
Closes: https://lore.kernel.org/linux-can/CAGp+u1aBK8QVjsvAxM2Ldzep4rEbsP9x_pV3At4g=h1kVEtyhA@mail.gmail.com/
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 51 insertions(+), 14 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index bdf53241bd7b..b612135b017d 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1321,10 +1321,15 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
bcm_rx_handler, op,
"bcm", sk);
op->rx_reg_dev = dev;
dev_put(dev);
+ } else {
+ /* the requested device is gone - do not
+ * silently succeed without registering
+ */
+ err = -ENODEV;
}
} else
err = can_rx_register(sock_net(sk), NULL, op->can_id,
REGMASK(op->can_id),
@@ -1394,16 +1399,17 @@ static int bcm_tx_send(struct msghdr *msg, int ifindex, struct sock *sk,
*/
static int bcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
{
struct sock *sk = sock->sk;
struct bcm_sock *bo = bcm_sk(sk);
- int ifindex = bo->ifindex; /* default ifindex for this bcm_op */
+ int ifindex;
struct bcm_msg_head msg_head;
int cfsiz;
int ret; /* read bytes or error codes as return value */
- if (!bo->bound)
+ /* Lockless fast-path check for bound socket */
+ if (!READ_ONCE(bo->bound))
return -ENOTCONN;
/* check for valid message length from userspace */
if (size < MHSIZ)
return -EINVAL;
@@ -1415,43 +1421,65 @@ static int bcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
cfsiz = CFSIZ(msg_head.flags);
if ((size - MHSIZ) % cfsiz)
return -EINVAL;
+ lock_sock(sk);
+
+ /* Re-validate under the socket lock: a concurrent bcm_notify()
+ * may have unbound this socket (device removal) after the
+ * lockless fast-path check above. bo->ifindex is only ever
+ * mutated under lock_sock(), so reading it here - instead of
+ * before taking the lock - guarantees it can't be observed
+ * torn against bo->bound.
+ */
+ if (!bo->bound) {
+ ret = -ENOTCONN;
+ goto out_release;
+ }
+
+ /* default ifindex for this bcm_op */
+ ifindex = bo->ifindex;
+
/* check for alternative ifindex for this bcm_op */
if (!ifindex && msg->msg_name) {
/* no bound device as default => check msg_name */
DECLARE_SOCKADDR(struct sockaddr_can *, addr, msg->msg_name);
- if (msg->msg_namelen < BCM_MIN_NAMELEN)
- return -EINVAL;
+ if (msg->msg_namelen < BCM_MIN_NAMELEN) {
+ ret = -EINVAL;
+ goto out_release;
+ }
- if (addr->can_family != AF_CAN)
- return -EINVAL;
+ if (addr->can_family != AF_CAN) {
+ ret = -EINVAL;
+ goto out_release;
+ }
/* ifindex from sendto() */
ifindex = addr->can_ifindex;
if (ifindex) {
struct net_device *dev;
dev = dev_get_by_index(sock_net(sk), ifindex);
- if (!dev)
- return -ENODEV;
+ if (!dev) {
+ ret = -ENODEV;
+ goto out_release;
+ }
if (dev->type != ARPHRD_CAN) {
dev_put(dev);
- return -ENODEV;
+ ret = -ENODEV;
+ goto out_release;
}
dev_put(dev);
}
}
- lock_sock(sk);
-
switch (msg_head.opcode) {
case TX_SETUP:
ret = bcm_tx_setup(&msg_head, msg, ifindex, sk);
break;
@@ -1497,10 +1525,11 @@ static int bcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
default:
ret = -EINVAL;
break;
}
+out_release:
release_sock(sk);
return ret;
}
@@ -1533,11 +1562,16 @@ static void bcm_notify(struct bcm_sock *bo, unsigned long msg,
if (sock_net(sk)->can.bcmproc_dir && bo->bcm_proc_read) {
remove_proc_entry(bo->procname, sock_net(sk)->can.bcmproc_dir);
bo->bcm_proc_read = NULL;
}
#endif
- bo->bound = 0;
+ /* Paired with the lockless fast-path check in
+ * bcm_sendmsg(); bo->ifindex itself is only ever
+ * accessed under lock_sock() so it needs no
+ * annotation.
+ */
+ WRITE_ONCE(bo->bound, 0);
bo->ifindex = 0;
notify_enodev = 1;
}
release_sock(sk);
@@ -1674,11 +1708,11 @@ static int bcm_release(struct socket *sock)
list_for_each_entry_safe(op, next, &bo->rx_ops, list)
bcm_remove_op(op);
/* remove device reference */
if (bo->bound) {
- bo->bound = 0;
+ WRITE_ONCE(bo->bound, 0);
bo->ifindex = 0;
}
sock_orphan(sk);
sock->sk = NULL;
@@ -1744,11 +1778,14 @@ static int bcm_connect(struct socket *sock, struct sockaddr_unsized *uaddr, int
goto fail;
}
}
#endif /* CONFIG_PROC_FS */
- bo->bound = 1;
+ /* bo->ifindex above is fully assigned before this point; pairs
+ * with the lockless fast-path check in bcm_sendmsg()
+ */
+ WRITE_ONCE(bo->bound, 1);
fail:
release_sock(sk);
return ret;
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread* Re: [PATCH v9 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
2026-07-09 8:16 ` [PATCH v9 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:36 ` sashiko-bot
0 siblings, 0 replies; 16+ messages in thread
From: sashiko-bot @ 2026-07-09 8:36 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Vincent Mailhol, Oliver Hartkopp, linux-can, Marc Kleine-Budde,
Oleksij Rempel
Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
Pre-existing issues:
- [High] Unsafe lockless list traversal and missing memory barriers for tx_ops and rx_ops lists.
- [High] Unbounded allocation of bcm_op structures allows local users to exhaust kernel memory.
- [Medium] bcm_rx_setup() silently fails to resume frame delivery for an updated RX operation if the target network device was previously unregistered.
- [Medium] Data race on bo->ifindex and bo->bound during NETDEV_DOWN handling risks torn reads and spurious errors.
--
--- Patch [2]: [PATCH v9 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure ---
commit 48dc89358d05a6bfc0097f061749b853a77c5328
Author: Oliver Hartkopp <socketcan@hartkopp.net>
Subject: can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
This commit fixes a data race between lockless reads of bo->bound and
bo->ifindex in bcm_sendmsg() and locked updates in bcm_notify() and other
paths. It also addresses a silent failure in bcm_rx_setup() when the
requested target device concurrently disappears.
Link: Closes: https://lore.kernel.org/linux-can/CAGp+u1aBK8QVjsvAxM2Ldzep4rEbsP9x_pV3At4g=h1kVEtyhA@mail.gmail.com/
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
> @@ -1323,6 +1323,11 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
>
> op->rx_reg_dev = dev;
> dev_put(dev);
> + } else {
> + /* the requested device is gone - do not
> + * silently succeed without registering
> + */
> + err = -ENODEV;
> }
[Severity: High]
This is a pre-existing issue, but does the current iteration logic for
bo->tx_ops and bo->rx_ops in bcm_proc_show() risk wild memory accesses or
infinite loops?
bcm_proc_show() iterates over the operations holding only rcu_read_lock():
net/can/bcm.c:bcm_proc_show() {
...
list_for_each_entry_rcu(op, &bo->rx_ops, list) { ... }
...
list_for_each_entry(op, &bo->tx_ops, list) { ... }
}
Meanwhile, bcm_rx_setup() and bcm_tx_setup() insert new elements without
an RCU write memory barrier:
net/can/bcm.c:bcm_rx_setup() {
...
/* add this bcm_op to the list of the rx_ops */
list_add(&op->list, &bo->rx_ops);
}
Could this allow a local user reading /proc/net/can-bcm to crash the
system while operations are concurrently registered?
[Severity: High]
This isn't a bug introduced by this patch, but is it possible for local
users to exhaust kernel memory by creating a large number of BCM operations?
In bcm_rx_setup() and bcm_tx_setup(), new operation structures and their
associated frame arrays are allocated unboundedly:
net/can/bcm.c:bcm_rx_setup() {
...
op = kzalloc(OPSIZ, GFP_KERNEL);
...
op->frames = kmalloc_array(msg_head->nframes, op->cfsiz, GFP_KERNEL);
}
Since these allocations do not appear to enforce any per-socket limit
or charge the socket's memory quota (sk_rmem_alloc/sk_wmem_alloc), could an
unprivileged user repeatedly call sendmsg() with unique can_ids to trigger
an out-of-memory panic?
[Severity: Medium]
This is a pre-existing issue, but does bcm_rx_setup() silently fail to
resume frame delivery for updated RX operations if the target interface was
cycled?
When an interface is removed, bcm_notify() handles NETDEV_UNREGISTER by
unregistering the filter and setting op->rx_reg_dev = NULL, but leaves the
op in the active bo->rx_ops list:
net/can/bcm.c:bcm_rx_unreg() {
...
/* mark as removed subscription */
op->rx_reg_dev = NULL;
}
If an RX_SETUP request subsequently attempts to update this existing
filter, bcm_rx_setup() skips re-registration:
net/can/bcm.c:bcm_rx_setup() {
...
/* Only an update -> do not call can_rx_register() */
do_rx_register = 0;
}
Should this logic check if the operation is currently unregistered before
clearing do_rx_register?
[ ... ]
> @@ -1535,7 +1564,12 @@ static void bcm_notify(struct bcm_sock *bo, unsigned long msg,
> bo->bcm_proc_read = NULL;
> }
> #endif
> - bo->bound = 0;
> + /* Paired with the lockless fast-path check in
> + * bcm_sendmsg(); bo->ifindex itself is only ever
> + * accessed under lock_sock() so it needs no
> + * annotation.
> + */
> + WRITE_ONCE(bo->bound, 0);
> bo->ifindex = 0;
> notify_enodev = 1;
> }
[Severity: Medium]
This isn't a bug introduced by this patch, but does the handling of
NETDEV_DOWN in bcm_notify() have a data race on bo->ifindex and bo->bound?
While the target patch adds WRITE_ONCE() for bo->bound during device
removal, NETDEV_DOWN appears to read these fields locklessly:
net/can/bcm.c:bcm_notify() {
...
case NETDEV_DOWN:
if (bo->bound && bo->ifindex == dev->ifindex) {
}
If a socket is connecting to a new device while an unrelated device goes
down, could the lack of barriers allow bcm_notify() to observe a new
bo->bound=1 but the old bo->ifindex, leading to a spurious ENETDOWN error?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v9-0-6eebb78ccfb2@hartkopp.net?part=2
^ permalink raw reply [flat|nested] 16+ messages in thread
* [PATCH v9 03/10] can: bcm: add locking when updating filter and timer values
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
2026-07-09 8:16 ` [PATCH v9 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
2026-07-09 8:16 ` [PATCH v9 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:31 ` sashiko-bot
2026-07-09 8:16 ` [PATCH v9 04/10] can: bcm: fix CAN frame rx/tx statistics Oliver Hartkopp via B4 Relay
` (6 subsequent siblings)
9 siblings, 1 reply; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde, syzbot+75e5e4ae00c3b4bb544e
From: Oliver Hartkopp <socketcan@hartkopp.net>
KCSAN detected a simultaneous access to timer values that can be
overwritten in bcm_rx_setup() when updating timer and filter content
while bcm_rx_handler(), bcm_rx_timeout_handler() or bcm_rx_thr_handler()
run concurrently on incoming CAN traffic.
Protect the timer (ival1/ival2/kt_ival1/kt_ival2/kt_lastmsg) and filter
(nframes/flags/frames/last_frames) updates in bcm_rx_setup() with a new
per-op bcm_rx_update_lock, taken with the matching scope in the RX
handlers. memcpy_from_msg() is staged into a temporary buffer before the
lock is taken, since it can sleep and must not run under a spinlock.
hrtimer_cancel() is always called without bcm_rx_update_lock held, since
bcm_rx_timeout_handler()/bcm_rx_thr_handler() take the same lock and a
running callback would otherwise deadlock against the canceller.
Also close a related race: bcm_rx_setup() cleared the RTR flag in the
stored reply frame's can_id as a separate, unprotected step after the
frame content was already installed, so a concurrent bcm_rx_handler()
could transmit a stale reply with CAN_RTR_FLAG still set. Fold that
normalization into the initial frame preparation instead (on the staged
buffer for updates, directly on op->frames pre-registration for new
ops), so the installed frame is always atomically self-consistent.
bcm_rx_handler()'s RX_RTR_FRAME check now takes a lock-protected
snapshot of op->flags before deciding whether to call bcm_can_tx(),
but does not hold the lock across that call.
Also take a lock-protected snapshot of the currframe in bcm_can_tx()
to avoid partly overwrites by content updates in bcm_tx_setup().
Omit calling hrtimer_forward() with zero interval in bcm_rx_thr_handler().
kt_ival2 may have been concurrently cleared by bcm_rx_setup() before it
cancels this timer, so check kt_ival2 inside the bcm_rx_update_lock.
Fixes: c2aba69d0c36 ("can: bcm: add locking for bcm_op runtime updates")
Reported-by: syzbot+75e5e4ae00c3b4bb544e@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-can/6975d5cf.a00a0220.33ccc7.0022.GAE@google.com/
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 136 ++++++++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 104 insertions(+), 32 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index b612135b017d..af4bb4182bc2 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -127,10 +127,11 @@ struct bcm_op {
struct canfd_frame sframe;
struct canfd_frame last_sframe;
struct sock *sk;
struct net_device *rx_reg_dev;
spinlock_t bcm_tx_lock; /* protect currframe/count in runtime updates */
+ spinlock_t bcm_rx_update_lock; /* protect filter/timer data updates */
};
struct bcm_sock {
struct sock sk;
int bound;
@@ -291,26 +292,30 @@ static int bcm_proc_show(struct seq_file *m, void *v)
/*
* bcm_can_tx - send the (next) CAN frame to the appropriate CAN interface
* of the given bcm tx op
*/
-static void bcm_can_tx(struct bcm_op *op)
+static void bcm_can_tx(struct bcm_op *op, struct canfd_frame *cf)
{
struct sk_buff *skb;
struct can_skb_ext *csx;
struct net_device *dev;
- struct canfd_frame *cf;
+ struct canfd_frame cframe;
int err;
/* no target device? => exit */
if (!op->ifindex)
return;
- /* read currframe under lock protection */
- spin_lock_bh(&op->bcm_tx_lock);
- cf = op->frames + op->cfsiz * op->currframe;
- spin_unlock_bh(&op->bcm_tx_lock);
+ if (!cf) {
+ /* read currframe under lock protection */
+ spin_lock_bh(&op->bcm_tx_lock);
+ memcpy(&cframe, op->frames + op->cfsiz * op->currframe,
+ op->cfsiz);
+ cf = &cframe;
+ spin_unlock_bh(&op->bcm_tx_lock);
+ }
dev = dev_get_by_index(sock_net(op->sk), op->ifindex);
if (!dev) {
/* RFC: should this bcm_op remove itself here? */
return;
@@ -459,11 +464,11 @@ static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
{
struct bcm_op *op = container_of(hrtimer, struct bcm_op, timer);
struct bcm_msg_head msg_head;
if (op->kt_ival1 && (op->count > 0)) {
- bcm_can_tx(op);
+ bcm_can_tx(op, NULL);
if (!op->count && (op->flags & TX_COUNTEVT)) {
/* create notification to user */
memset(&msg_head, 0, sizeof(msg_head));
msg_head.opcode = TX_EXPIRED;
@@ -476,11 +481,11 @@ static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
bcm_send_to_user(op, &msg_head, NULL, 0);
}
} else if (op->kt_ival2) {
- bcm_can_tx(op);
+ bcm_can_tx(op, NULL);
}
return bcm_tx_set_expiry(op, &op->timer) ?
HRTIMER_RESTART : HRTIMER_NORESTART;
}
@@ -620,10 +625,12 @@ static void bcm_rx_starttimer(struct bcm_op *op)
static enum hrtimer_restart bcm_rx_timeout_handler(struct hrtimer *hrtimer)
{
struct bcm_op *op = container_of(hrtimer, struct bcm_op, timer);
struct bcm_msg_head msg_head;
+ spin_lock_bh(&op->bcm_rx_update_lock);
+
/* if user wants to be informed, when cyclic CAN-Messages come back */
if ((op->flags & RX_ANNOUNCE_RESUME) && op->last_frames) {
/* clear received CAN frames to indicate 'nothing received' */
memset(op->last_frames, 0, op->nframes * op->cfsiz);
}
@@ -636,10 +643,12 @@ static enum hrtimer_restart bcm_rx_timeout_handler(struct hrtimer *hrtimer)
msg_head.ival1 = op->ival1;
msg_head.ival2 = op->ival2;
msg_head.can_id = op->can_id;
msg_head.nframes = 0;
+ spin_unlock_bh(&op->bcm_rx_update_lock);
+
bcm_send_to_user(op, &msg_head, NULL, 0);
return HRTIMER_NORESTART;
}
@@ -684,30 +693,43 @@ static int bcm_rx_thr_flush(struct bcm_op *op)
* Check for throttled data and send it to the userspace
*/
static enum hrtimer_restart bcm_rx_thr_handler(struct hrtimer *hrtimer)
{
struct bcm_op *op = container_of(hrtimer, struct bcm_op, thrtimer);
+ enum hrtimer_restart ret;
+
+ spin_lock_bh(&op->bcm_rx_update_lock);
- if (bcm_rx_thr_flush(op)) {
+ /* kt_ival2 may have been concurrently cleared by bcm_rx_setup()
+ * before it cancels this timer - never forward with a zero
+ * interval in that case.
+ */
+ if (bcm_rx_thr_flush(op) && op->kt_ival2) {
hrtimer_forward_now(hrtimer, op->kt_ival2);
- return HRTIMER_RESTART;
+ ret = HRTIMER_RESTART;
} else {
/* rearm throttle handling */
op->kt_lastmsg = 0;
- return HRTIMER_NORESTART;
+ ret = HRTIMER_NORESTART;
}
+
+ spin_unlock_bh(&op->bcm_rx_update_lock);
+
+ return ret;
}
/*
* bcm_rx_handler - handle a CAN frame reception
*/
static void bcm_rx_handler(struct sk_buff *skb, void *data)
{
struct bcm_op *op = (struct bcm_op *)data;
const struct canfd_frame *rxframe = (struct canfd_frame *)skb->data;
+ struct canfd_frame rtrframe;
unsigned int i;
unsigned char traffic_flags;
+ bool rtr_frame;
if (op->can_id != rxframe->can_id)
return;
/* make sure to handle the correct frame type (CAN / CAN FD) */
@@ -727,13 +749,22 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
/* save originator for recvfrom() */
op->rx_ifindex = skb->dev->ifindex;
/* update statistics */
op->frames_abs++;
- if (op->flags & RX_RTR_FRAME) {
+ /* snapshot the flag under lock: op->flags/op->frames may be updated
+ * concurrently by bcm_rx_setup().
+ */
+ spin_lock_bh(&op->bcm_rx_update_lock);
+ rtr_frame = op->flags & RX_RTR_FRAME;
+ if (rtr_frame)
+ memcpy(&rtrframe, op->frames, op->cfsiz);
+ spin_unlock_bh(&op->bcm_rx_update_lock);
+
+ if (rtr_frame) {
/* send reply for RTR-request (placed in op->frames[0]) */
- bcm_can_tx(op);
+ bcm_can_tx(op, &rtrframe);
return;
}
/* compute flags to distinguish between own/local/remote CAN traffic */
traffic_flags = 0;
@@ -741,10 +772,12 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
traffic_flags |= RX_LOCAL;
if (skb->sk == op->sk)
traffic_flags |= RX_OWN;
}
+ spin_lock_bh(&op->bcm_rx_update_lock);
+
if (op->flags & RX_FILTER_ID) {
/* the easiest case */
bcm_rx_update_and_send(op, op->last_frames, rxframe,
traffic_flags);
goto rx_starttimer;
@@ -776,10 +809,12 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
}
}
rx_starttimer:
bcm_rx_starttimer(op);
+
+ spin_unlock_bh(&op->bcm_rx_update_lock);
}
/*
* helpers for bcm_op handling: find & delete bcm [rx|tx] op elements
*/
@@ -1114,11 +1149,11 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
/* spec: send CAN frame when starting timer */
op->flags |= TX_ANNOUNCE;
}
if (op->flags & TX_ANNOUNCE)
- bcm_can_tx(op);
+ bcm_can_tx(op, NULL);
if (op->flags & STARTTIMER)
bcm_tx_start_timer(op);
return msg_head->nframes * op->cfsiz + MHSIZ;
@@ -1128,10 +1163,28 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
kfree(op->frames);
kfree(op);
return err;
}
+static void bcm_rx_setup_rtr_check(struct bcm_msg_head *msg_head,
+ struct bcm_op *op, void *new_frames)
+{
+ /* funny feature in RX(!)_SETUP only for RTR-mode:
+ * copy can_id into frame BUT without RTR-flag to
+ * prevent a full-load-loopback-test ... ;-]
+ * normalize this on the staged buffer, before it is
+ * ever installed into op->frames.
+ */
+ if (msg_head->flags & RX_RTR_FRAME) {
+ struct canfd_frame *frame0 = new_frames;
+
+ if ((msg_head->flags & TX_CP_CAN_ID) ||
+ frame0->can_id == op->can_id)
+ frame0->can_id = op->can_id & ~CAN_RTR_FLAG;
+ }
+}
+
/*
* bcm_rx_setup - create or update a bcm rx op (for bcm_sendmsg)
*/
static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
int ifindex, struct sock *sk)
@@ -1162,10 +1215,12 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
return -EINVAL;
/* check the given can_id */
op = bcm_find_op(&bo->rx_ops, msg_head, ifindex);
if (op) {
+ void *new_frames = NULL;
+
/* update existing BCM operation */
/*
* Do we need more space for the CAN frames than currently
* allocated? -> This is a _really_ unusual use-case and
@@ -1173,33 +1228,55 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
*/
if (msg_head->nframes > op->nframes)
return -E2BIG;
if (msg_head->nframes) {
- /* update CAN frames content */
- err = memcpy_from_msg(op->frames, msg,
+ /* get new CAN frames content before locking */
+ new_frames = kmalloc(msg_head->nframes * op->cfsiz,
+ GFP_KERNEL);
+ if (!new_frames)
+ return -ENOMEM;
+
+ err = memcpy_from_msg(new_frames, msg,
msg_head->nframes * op->cfsiz);
- if (err < 0)
+ if (err < 0) {
+ kfree(new_frames);
return err;
+ }
- /* clear last_frames to indicate 'nothing received' */
- memset(op->last_frames, 0, msg_head->nframes * op->cfsiz);
+ bcm_rx_setup_rtr_check(msg_head, op, new_frames);
}
+ spin_lock_bh(&op->bcm_rx_update_lock);
op->nframes = msg_head->nframes;
op->flags = msg_head->flags;
+ if (msg_head->nframes) {
+ /* update CAN frames content */
+ memcpy(op->frames, new_frames,
+ msg_head->nframes * op->cfsiz);
+
+ /* clear last_frames to indicate 'nothing received' */
+ memset(op->last_frames, 0,
+ msg_head->nframes * op->cfsiz);
+ }
+ spin_unlock_bh(&op->bcm_rx_update_lock);
+
+ /* free temporary frames / kfree(NULL) is safe */
+ kfree(new_frames);
+
/* Only an update -> do not call can_rx_register() */
do_rx_register = 0;
} else {
/* insert new BCM operation for the given can_id */
op = kzalloc(OPSIZ, GFP_KERNEL);
if (!op)
return -ENOMEM;
spin_lock_init(&op->bcm_tx_lock);
+ spin_lock_init(&op->bcm_rx_update_lock);
op->can_id = msg_head->can_id;
op->nframes = msg_head->nframes;
op->cfsiz = CFSIZ(msg_head->flags);
op->flags = msg_head->flags;
@@ -1237,10 +1314,12 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
if (op->last_frames != &op->last_sframe)
kfree(op->last_frames);
kfree(op);
return err;
}
+
+ bcm_rx_setup_rtr_check(msg_head, op, op->frames);
}
/* bcm_can_tx / bcm_tx_timeout_handler needs this */
op->sk = sk;
sock_hold(sk);
@@ -1264,45 +1343,38 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
} /* if ((op = bcm_find_op(&bo->rx_ops, msg_head->can_id, ifindex))) */
/* check flags */
if (op->flags & RX_RTR_FRAME) {
- struct canfd_frame *frame0 = op->frames;
-
/* no timers in RTR-mode */
hrtimer_cancel(&op->thrtimer);
hrtimer_cancel(&op->timer);
-
- /*
- * funny feature in RX(!)_SETUP only for RTR-mode:
- * copy can_id into frame BUT without RTR-flag to
- * prevent a full-load-loopback-test ... ;-]
- */
- if ((op->flags & TX_CP_CAN_ID) ||
- (frame0->can_id == op->can_id))
- frame0->can_id = op->can_id & ~CAN_RTR_FLAG;
-
} else {
if (op->flags & SETTIMER) {
/* set timer value */
+ spin_lock_bh(&op->bcm_rx_update_lock);
op->ival1 = msg_head->ival1;
op->ival2 = msg_head->ival2;
op->kt_ival1 = bcm_timeval_to_ktime(msg_head->ival1);
op->kt_ival2 = bcm_timeval_to_ktime(msg_head->ival2);
+ op->kt_lastmsg = 0;
+ spin_unlock_bh(&op->bcm_rx_update_lock);
/* disable an active timer due to zero value? */
if (!op->kt_ival1)
hrtimer_cancel(&op->timer);
/*
* In any case cancel the throttle timer, flush
* potentially blocked msgs and reset throttle handling
*/
- op->kt_lastmsg = 0;
hrtimer_cancel(&op->thrtimer);
+
+ spin_lock_bh(&op->bcm_rx_update_lock);
bcm_rx_thr_flush(op);
+ spin_unlock_bh(&op->bcm_rx_update_lock);
}
if ((op->flags & STARTTIMER) && op->kt_ival1)
hrtimer_start(&op->timer, op->kt_ival1,
HRTIMER_MODE_REL_SOFT);
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread* Re: [PATCH v9 03/10] can: bcm: add locking when updating filter and timer values
2026-07-09 8:16 ` [PATCH v9 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:31 ` sashiko-bot
0 siblings, 0 replies; 16+ messages in thread
From: sashiko-bot @ 2026-07-09 8:31 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Vincent Mailhol, Marc Kleine-Budde, Oliver Hartkopp, linux-can,
Oleksij Rempel
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues:
- [Medium] Lockless updates of RX metadata (`rx_stamp`, `rx_ifindex`, `frames_abs`) lead to torn reads, lost increments, and corrupted timestamps.
--
--- Patch [3]: [PATCH v9 03/10] can: bcm: add locking when updating filter and timer values ---
commit 10b4ca432b89b6bdfb7aab7948a13f81a6bc41ed
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: add locking when updating filter and timer values
This commit introduces bcm_rx_update_lock to protect the filter and timer
configurations of a bcm_op structure from concurrent accesses. It ensures
that updates via bcm_rx_setup and usages in Rx and timeout handlers do not
race.
Link: https://lore.kernel.org/linux-can/6975d5cf.a00a0220.33ccc7.0022.GAE@google.com/
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index b612135b017d1..af4bb4182bc29 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
[ ... ]
> @@ -729,9 +751,18 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
> /* update statistics */
> op->frames_abs++;
>
> - if (op->flags & RX_RTR_FRAME) {
> + /* snapshot the flag under lock: op->flags/op->frames may be updated
> + * concurrently by bcm_rx_setup().
> + */
> + spin_lock_bh(&op->bcm_rx_update_lock);
[Severity: Medium]
This is a pre-existing issue, but should the update to op->frames_abs be
protected by the new bcm_rx_update_lock?
If a bcm_op is configured to listen on all interfaces (ifindex == 0) and
receives frames concurrently on multiple CAN interfaces, bcm_rx_handler()
can execute simultaneously on different CPUs.
Because op->frames_abs is updated outside the lock, concurrent writes can
occur, potentially leading to lost statistical increments. Additionally, on
32-bit systems, concurrent writes to 64-bit metadata fields like
op->rx_stamp could lead to torn reads when userspace retrieves them.
Could these metadata fields be moved inside the lock to prevent data
races?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v9-0-6eebb78ccfb2@hartkopp.net?part=3
^ permalink raw reply [flat|nested] 16+ messages in thread
* [PATCH v9 04/10] can: bcm: fix CAN frame rx/tx statistics
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
` (2 preceding siblings ...)
2026-07-09 8:16 ` [PATCH v9 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:31 ` sashiko-bot
2026-07-09 8:16 ` [PATCH v9 05/10] can: bcm: add missing rcu list annotations and operations Oliver Hartkopp via B4 Relay
` (5 subsequent siblings)
9 siblings, 1 reply; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde
From: Oliver Hartkopp <socketcan@hartkopp.net>
KCSAN detected a data race within the bcm_rx_handler() when two CAN frames
have been simultaneously received and processed in a single rx op by two
different CPUs.
Use atomic operations with (signed) long data types to access the
statistics in the hot path to fix the KCSAN complaint.
Additionally simplify the update and check of statistics overflow by
using the atomic operations in separate bcm_update_[rx|tx]_stats()
functions. The rx variant runs under bcm_rx_update_lock to prevent
races when resetting the two rx counters; the tx variant runs under
bcm_tx_lock and only needs to guard its own counter's overflow.
As the rx path resets its values already at LONG_MAX / 100, there is
no conflict between the two locking domains (bcm_rx_update_lock vs.
bcm_tx_lock) even for ops that use both paths.
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 56 +++++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 39 insertions(+), 17 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index af4bb4182bc2..1623a402600c 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -110,11 +110,11 @@ struct bcm_op {
struct rcu_head rcu;
struct work_struct work;
int ifindex;
canid_t can_id;
u32 flags;
- unsigned long frames_abs, frames_filtered;
+ atomic_long_t frames_abs, frames_filtered;
struct bcm_timeval ival1, ival2;
struct hrtimer timer, thrtimer;
ktime_t rx_stamp, kt_ival1, kt_ival2, kt_lastmsg;
int rx_ifindex;
int cfsiz;
@@ -227,14 +227,17 @@ static int bcm_proc_show(struct seq_file *m, void *v)
rcu_read_lock();
list_for_each_entry_rcu(op, &bo->rx_ops, list) {
- unsigned long reduction;
+ long reduction, frames_filtered, frames_abs;
+
+ frames_filtered = atomic_long_read(&op->frames_filtered);
+ frames_abs = atomic_long_read(&op->frames_abs);
/* print only active entries & prevent division by zero */
- if (!op->frames_abs)
+ if (!frames_abs)
continue;
seq_printf(m, "rx_op: %03X %-5s ", op->can_id,
bcm_proc_getifname(net, ifname, op->ifindex));
@@ -252,13 +255,13 @@ static int bcm_proc_show(struct seq_file *m, void *v)
if (op->kt_ival2)
seq_printf(m, "thr=%lld ",
(long long)ktime_to_us(op->kt_ival2));
seq_printf(m, "# recv %ld (%ld) => reduction: ",
- op->frames_filtered, op->frames_abs);
+ frames_filtered, frames_abs);
- reduction = 100 - (op->frames_filtered * 100) / op->frames_abs;
+ reduction = 100 - (frames_filtered * 100) / frames_abs;
seq_printf(m, "%s%ld%%\n",
(reduction == 100) ? "near " : "", reduction);
}
@@ -278,20 +281,39 @@ static int bcm_proc_show(struct seq_file *m, void *v)
if (op->kt_ival2)
seq_printf(m, "t2=%lld ",
(long long)ktime_to_us(op->kt_ival2));
- seq_printf(m, "# sent %ld\n", op->frames_abs);
+ seq_printf(m, "# sent %ld\n",
+ atomic_long_read(&op->frames_abs));
}
seq_putc(m, '\n');
rcu_read_unlock();
return 0;
}
#endif /* CONFIG_PROC_FS */
+static void bcm_update_rx_stats(struct bcm_op *op)
+{
+ /* prevent overflow of the reduction% calculation in bcm_proc_show() */
+ if (atomic_long_inc_return(&op->frames_abs) > LONG_MAX / 100) {
+ atomic_long_set(&op->frames_filtered, 0);
+ atomic_long_set(&op->frames_abs, 0);
+ }
+}
+
+static void bcm_update_tx_stats(struct bcm_op *op)
+{
+ /* tx_op has no reduction% calculation - use the full range and
+ * just keep the displayed counter non-negative on overflow
+ */
+ if (atomic_long_inc_return(&op->frames_abs) == LONG_MAX)
+ atomic_long_set(&op->frames_abs, 0);
+}
+
/*
* bcm_can_tx - send the (next) CAN frame to the appropriate CAN interface
* of the given bcm tx op
*/
static void bcm_can_tx(struct bcm_op *op, struct canfd_frame *cf)
@@ -342,11 +364,11 @@ static void bcm_can_tx(struct bcm_op *op, struct canfd_frame *cf)
/* update currframe and count under lock protection */
spin_lock_bh(&op->bcm_tx_lock);
if (!err)
- op->frames_abs++;
+ bcm_update_tx_stats(op);
op->currframe++;
/* reached last frame? */
if (op->currframe >= op->nframes)
@@ -495,16 +517,13 @@ static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
*/
static void bcm_rx_changed(struct bcm_op *op, struct canfd_frame *data)
{
struct bcm_msg_head head;
- /* update statistics */
- op->frames_filtered++;
-
- /* prevent statistics overflow */
- if (op->frames_filtered > ULONG_MAX/100)
- op->frames_filtered = op->frames_abs = 0;
+ /* update statistics (frames_filtered <= frames_abs) */
+ if (atomic_long_read(&op->frames_abs))
+ atomic_long_inc(&op->frames_filtered);
/* this element is not throttled anymore */
data->flags &= ~RX_THR;
memset(&head, 0, sizeof(head));
@@ -746,20 +765,23 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
/* save rx timestamp */
op->rx_stamp = skb->tstamp;
/* save originator for recvfrom() */
op->rx_ifindex = skb->dev->ifindex;
- /* update statistics */
- op->frames_abs++;
- /* snapshot the flag under lock: op->flags/op->frames may be updated
- * concurrently by bcm_rx_setup().
+ /* snapshot RTR content under lock: op->flags/op->frames may be
+ * updated concurrently by bcm_rx_setup().
*/
spin_lock_bh(&op->bcm_rx_update_lock);
+
+ /* update statistics with lock analogue to bcm_rx_changed() callers */
+ bcm_update_rx_stats(op);
+
rtr_frame = op->flags & RX_RTR_FRAME;
if (rtr_frame)
memcpy(&rtrframe, op->frames, op->cfsiz);
+
spin_unlock_bh(&op->bcm_rx_update_lock);
if (rtr_frame) {
/* send reply for RTR-request (placed in op->frames[0]) */
bcm_can_tx(op, &rtrframe);
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread* Re: [PATCH v9 04/10] can: bcm: fix CAN frame rx/tx statistics
2026-07-09 8:16 ` [PATCH v9 04/10] can: bcm: fix CAN frame rx/tx statistics Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:31 ` sashiko-bot
0 siblings, 0 replies; 16+ messages in thread
From: sashiko-bot @ 2026-07-09 8:31 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Vincent Mailhol, Oliver Hartkopp, Marc Kleine-Budde, linux-can,
Oleksij Rempel
Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
New issues:
- [Medium] Lock dropping in bcm_rx_handler() allows frames_filtered to temporarily exceed frames_abs, breaking the invariant and causing negative reduction percentage calculations.
Pre-existing issues:
- [High] bcm_tx_setup modifies ktime_t timers, flags, and frames without holding bcm_tx_lock, allowing concurrent timers to read torn or corrupted data.
- [High] bcm_rx_handler races on op->rx_stamp and op->rx_ifindex updates outside bcm_rx_update_lock.
- [High] list_add() is used instead of list_add_rcu() when adding newly initialized bcm_op elements to the RCU-protected lists bo->tx_ops and bo->rx_ops.
--
--- Patch [4]: [PATCH v9 04/10] can: bcm: fix CAN frame rx/tx statistics ---
commit fe57f26f76b6c7f7c4b5702be973bf0265c694f1
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: fix CAN frame rx/tx statistics
This commit fixes a KCSAN data race complaint in the broadcast manager
receive handler when two CAN frames are processed simultaneously. It
switches to atomic types for statistics and refactors overflow handling.
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index af4bb4182bc29..1623a402600ce 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
[ ... ]
> @@ -229,10 +229,13 @@ static int bcm_proc_show(struct seq_file *m, void *v)
>
> list_for_each_entry_rcu(op, &bo->rx_ops, list) {
[Severity: High]
This isn't a bug introduced by this patch, but is it safe for bcm_rx_setup()
and bcm_tx_setup() to use list_add() when inserting new elements into these
lists?
Since bcm_proc_show() iterates over bo->rx_ops and bo->tx_ops using
list_for_each_entry_rcu(), using list_add() instead of list_add_rcu() during
insertion lacks the necessary memory barriers. Could this allow concurrent
RCU readers on weakly ordered architectures to observe uninitialized fields?
[ ... ]
> @@ -344,7 +366,7 @@ static void bcm_can_tx(struct bcm_op *op, struct canfd_frame *cf)
> spin_lock_bh(&op->bcm_tx_lock);
>
> if (!err)
> - op->frames_abs++;
> + bcm_update_tx_stats(op);
>
> op->currframe++;
[Severity: High]
This is a pre-existing issue, but does bcm_tx_setup() need to hold this same
bcm_tx_lock when modifying op->frames, op->flags, and the ktime_t timers?
When a user calls bcm_sendmsg() to update an existing TX op, these values are
modified without the lock. If a concurrent timer fires bcm_tx_timeout_handler()
or transmission occurs here via bcm_can_tx(), could it result in torn reads of
64-bit ktime_t timers on 32-bit systems, or the transmission of partially
updated CAN frames?
[ ... ]
> @@ -748,16 +767,19 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
> op->rx_stamp = skb->tstamp;
> /* save originator for recvfrom() */
> op->rx_ifindex = skb->dev->ifindex;
[Severity: High]
This is a pre-existing issue, but can these unprotected assignments cause a
metadata race?
If a socket is subscribed to all interfaces (ifindex == 0) and two frames are
received simultaneously on different interfaces, couldn't different CPUs
concurrently overwrite op->rx_stamp and op->rx_ifindex outside of
bcm_rx_update_lock? This might result in corrupted stream metadata when the
frames are eventually sent to userspace.
> - /* update statistics */
> - op->frames_abs++;
>
> - /* snapshot the flag under lock: op->flags/op->frames may be updated
> - * concurrently by bcm_rx_setup().
> + /* snapshot RTR content under lock: op->flags/op->frames may be
> + * updated concurrently by bcm_rx_setup().
> */
> spin_lock_bh(&op->bcm_rx_update_lock);
> +
> + /* update statistics with lock analogue to bcm_rx_changed() callers */
> + bcm_update_rx_stats(op);
> +
> rtr_frame = op->flags & RX_RTR_FRAME;
> if (rtr_frame)
> memcpy(&rtrframe, op->frames, op->cfsiz);
> +
> spin_unlock_bh(&op->bcm_rx_update_lock);
[Severity: Medium]
Can dropping the lock here allow frames_filtered to exceed frames_abs?
CPU 1 could increment frames_abs past the limit (LONG_MAX / 100) and reset
both counters to 0 inside bcm_update_rx_stats(), then drop the lock.
CPU 2 could then process a packet, acquire the lock, increment frames_abs to
1, and drop the lock.
Both CPUs would then proceed to their second lock section where
bcm_rx_changed() is called. Both would increment frames_filtered because
frames_abs is non-zero, leaving frames_filtered at 2 while frames_abs is 1.
Wouldn't this break the invariant and cause a negative reduction percentage to
be displayed in procfs?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v9-0-6eebb78ccfb2@hartkopp.net?part=4
^ permalink raw reply [flat|nested] 16+ messages in thread
* [PATCH v9 05/10] can: bcm: add missing rcu list annotations and operations
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
` (3 preceding siblings ...)
2026-07-09 8:16 ` [PATCH v9 04/10] can: bcm: fix CAN frame rx/tx statistics Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:16 ` [PATCH v9 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates Oliver Hartkopp via B4 Relay
` (4 subsequent siblings)
9 siblings, 0 replies; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde, sashiko-reviews
From: Oliver Hartkopp <socketcan@hartkopp.net>
sashiko-bot remarked the missing use of list_add_rcu() in
bcm_[rx|tx]_setup() to have a proper initialized bcm_op structure
when bcm_proc_show() traverses the bcm_op's under rcu_read_lock().
To cover all initial settings of the bcm_op's the list_add_rcu() calls
are moved to the end of the setup code.
While at it, also fix the mirroring removal side: bcm_release() called
bcm_remove_op() - which frees the op via call_rcu() - on ops that were
still linked in bo->tx_ops/bo->rx_ops, without list_del_rcu() first.
Unlink each op with list_del_rcu() before handing it to bcm_remove_op(),
matching the existing pattern in bcm_delete_tx_op()/bcm_delete_rx_op().
Reported-by: sashiko-reviews@lists.linux.dev
Closes: https://lore.kernel.org/linux-can/20260610094654.A1FFE1F00893@smtp.kernel.org/
Fixes: dac5e6249159 ("can: bcm: add missing rcu read protection for procfs content")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index 1623a402600c..0a7819bc891f 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -263,11 +263,11 @@ static int bcm_proc_show(struct seq_file *m, void *v)
seq_printf(m, "%s%ld%%\n",
(reduction == 100) ? "near " : "", reduction);
}
- list_for_each_entry(op, &bo->tx_ops, list) {
+ list_for_each_entry_rcu(op, &bo->tx_ops, list) {
seq_printf(m, "tx_op: %03X %s ", op->can_id,
bcm_proc_getifname(net, ifname, op->ifindex));
if (op->flags & CAN_FD_FRAME)
@@ -1006,10 +1006,11 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
int ifindex, struct sock *sk)
{
struct bcm_sock *bo = bcm_sk(sk);
struct bcm_op *op;
struct canfd_frame *cf;
+ bool add_op_to_list = false;
unsigned int i;
int err;
/* we need a real device to send frames */
if (!ifindex)
@@ -1147,12 +1148,11 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
/* currently unused in tx_ops */
hrtimer_setup(&op->thrtimer, hrtimer_dummy_timeout, CLOCK_MONOTONIC,
HRTIMER_MODE_REL_SOFT);
- /* add this bcm_op to the list of the tx_ops */
- list_add(&op->list, &bo->tx_ops);
+ add_op_to_list = true;
} /* if ((op = bcm_find_op(&bo->tx_ops, msg_head->can_id, ifindex))) */
if (op->flags & SETTIMER) {
/* set timer values */
@@ -1170,10 +1170,14 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
hrtimer_cancel(&op->timer);
/* spec: send CAN frame when starting timer */
op->flags |= TX_ANNOUNCE;
}
+ /* add this bcm_op to the list of the tx_ops? */
+ if (add_op_to_list)
+ list_add_rcu(&op->list, &bo->tx_ops);
+
if (op->flags & TX_ANNOUNCE)
bcm_can_tx(op, NULL);
if (op->flags & STARTTIMER)
bcm_tx_start_timer(op);
@@ -1354,13 +1358,10 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
hrtimer_setup(&op->timer, bcm_rx_timeout_handler, CLOCK_MONOTONIC,
HRTIMER_MODE_REL_SOFT);
hrtimer_setup(&op->thrtimer, bcm_rx_thr_handler, CLOCK_MONOTONIC,
HRTIMER_MODE_REL_SOFT);
- /* add this bcm_op to the list of the rx_ops */
- list_add(&op->list, &bo->rx_ops);
-
/* call can_rx_register() */
do_rx_register = 1;
} /* if ((op = bcm_find_op(&bo->rx_ops, msg_head->can_id, ifindex))) */
@@ -1428,14 +1429,16 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
err = can_rx_register(sock_net(sk), NULL, op->can_id,
REGMASK(op->can_id),
bcm_rx_handler, op, "bcm", sk);
if (err) {
/* this bcm rx op is broken -> remove it */
- list_del_rcu(&op->list);
bcm_remove_op(op);
return err;
}
+
+ /* add this bcm_op to the list of the rx_ops */
+ list_add_rcu(&op->list, &bo->rx_ops);
}
return msg_head->nframes * op->cfsiz + MHSIZ;
}
@@ -1765,12 +1768,14 @@ static int bcm_release(struct socket *sock)
/* remove procfs entry */
if (net->can.bcmproc_dir && bo->bcm_proc_read)
remove_proc_entry(bo->procname, net->can.bcmproc_dir);
#endif /* CONFIG_PROC_FS */
- list_for_each_entry_safe(op, next, &bo->tx_ops, list)
+ list_for_each_entry_safe(op, next, &bo->tx_ops, list) {
+ list_del_rcu(&op->list);
bcm_remove_op(op);
+ }
list_for_each_entry_safe(op, next, &bo->rx_ops, list) {
/*
* Don't care if we're bound or not (due to netdev problems)
* can_rx_unregister() is always a save thing to do here.
@@ -1797,12 +1802,14 @@ static int bcm_release(struct socket *sock)
}
synchronize_rcu();
- list_for_each_entry_safe(op, next, &bo->rx_ops, list)
+ list_for_each_entry_safe(op, next, &bo->rx_ops, list) {
+ list_del_rcu(&op->list);
bcm_remove_op(op);
+ }
/* remove device reference */
if (bo->bound) {
WRITE_ONCE(bo->bound, 0);
bo->ifindex = 0;
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread* [PATCH v9 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
` (4 preceding siblings ...)
2026-07-09 8:16 ` [PATCH v9 05/10] can: bcm: add missing rcu list annotations and operations Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:16 ` [PATCH v9 07/10] can: bcm: validate frame length in bcm_rx_setup() for RTR replies Oliver Hartkopp via B4 Relay
` (3 subsequent siblings)
9 siblings, 0 replies; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde
From: Oliver Hartkopp <socketcan@hartkopp.net>
Stage new CAN frame content for an existing tx op into a kmalloc()'d
buffer and validate it there, mirroring the approach already used in
bcm_rx_setup(). Only copy the validated data into op->frames while
holding op->bcm_tx_lock, so bcm_can_tx() and bcm_tx_timeout_handler()
can no longer observe a partially updated or unvalidated frame.
Add a missing error path for memcpy_from_msg() when copying CAN frame
data from userspace.
Also move the kt_ival1/kt_ival2/ival1/ival2 updates in bcm_tx_setup()
under op->bcm_tx_lock, and read kt_ival1/kt_ival2/count under the same
lock in bcm_tx_set_expiry() and bcm_tx_timeout_handler(), closing the
torn 64-bit ktime_t read on 32-bit platforms.
Fixes: c2aba69d0c36 ("can: bcm: add locking for bcm_op runtime updates")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 81 +++++++++++++++++++++++++++++++++++++++++------------------
1 file changed, 57 insertions(+), 24 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index 0a7819bc891f..de4ce01bdd04 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -126,11 +126,11 @@ struct bcm_op {
void *last_frames;
struct canfd_frame sframe;
struct canfd_frame last_sframe;
struct sock *sk;
struct net_device *rx_reg_dev;
- spinlock_t bcm_tx_lock; /* protect currframe/count in runtime updates */
+ spinlock_t bcm_tx_lock; /* protect tx data and timer updates */
spinlock_t bcm_rx_update_lock; /* protect filter/timer data updates */
};
struct bcm_sock {
struct sock sk;
@@ -462,16 +462,22 @@ static void bcm_send_to_user(struct bcm_op *op, struct bcm_msg_head *head,
static bool bcm_tx_set_expiry(struct bcm_op *op, struct hrtimer *hrt)
{
ktime_t ival;
+ spin_lock_bh(&op->bcm_tx_lock);
+
if (op->kt_ival1 && op->count)
ival = op->kt_ival1;
- else if (op->kt_ival2)
+ else if (op->kt_ival2) {
ival = op->kt_ival2;
- else
+ } else {
+ spin_unlock_bh(&op->bcm_tx_lock);
return false;
+ }
+
+ spin_unlock_bh(&op->bcm_tx_lock);
hrtimer_set_expires(hrt, ktime_add(ktime_get(), ival));
return true;
}
@@ -484,12 +490,21 @@ static void bcm_tx_start_timer(struct bcm_op *op)
/* bcm_tx_timeout_handler - performs cyclic CAN frame transmissions */
static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
{
struct bcm_op *op = container_of(hrtimer, struct bcm_op, timer);
struct bcm_msg_head msg_head;
+ bool tx_ival1, tx_ival2;
- if (op->kt_ival1 && (op->count > 0)) {
+ /* snapshot kt_ival1/kt_ival2/count under lock to avoid torn
+ * ktime_t reads racing with concurrent bcm_tx_setup() updates
+ */
+ spin_lock_bh(&op->bcm_tx_lock);
+ tx_ival1 = op->kt_ival1 && (op->count > 0);
+ tx_ival2 = !!op->kt_ival2;
+ spin_unlock_bh(&op->bcm_tx_lock);
+
+ if (tx_ival1) {
bcm_can_tx(op, NULL);
if (!op->count && (op->flags & TX_COUNTEVT)) {
/* create notification to user */
memset(&msg_head, 0, sizeof(msg_head));
@@ -502,11 +517,11 @@ static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
msg_head.nframes = 0;
bcm_send_to_user(op, &msg_head, NULL, 0);
}
- } else if (op->kt_ival2) {
+ } else if (tx_ival2) {
bcm_can_tx(op, NULL);
}
return bcm_tx_set_expiry(op, &op->timer) ?
HRTIMER_RESTART : HRTIMER_NORESTART;
@@ -1025,64 +1040,80 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
return -EINVAL;
/* check the given can_id */
op = bcm_find_op(&bo->tx_ops, msg_head, ifindex);
if (op) {
+ void *new_frames;
+
/* update existing BCM operation */
/*
* Do we need more space for the CAN frames than currently
* allocated? -> This is a _really_ unusual use-case and
* therefore (complexity / locking) it is not supported.
*/
if (msg_head->nframes > op->nframes)
return -E2BIG;
- /* update CAN frames content */
+ /* get new CAN frames content into a staging buffer before
+ * locking: validate and normalize the frames there so that
+ * bcm_can_tx() / bcm_tx_timeout_handler() never observe a
+ * partially updated or unvalidated frame in op->frames
+ */
+ new_frames = kmalloc(msg_head->nframes * op->cfsiz, GFP_KERNEL);
+ if (!new_frames)
+ return -ENOMEM;
+
for (i = 0; i < msg_head->nframes; i++) {
- cf = op->frames + op->cfsiz * i;
+ cf = new_frames + op->cfsiz * i;
err = memcpy_from_msg((u8 *)cf, msg, op->cfsiz);
+ if (err < 0) {
+ kfree(new_frames);
+ return err;
+ }
if (op->flags & CAN_FD_FRAME) {
if (cf->len > 64)
err = -EINVAL;
} else {
if (cf->len > 8)
err = -EINVAL;
}
- if (err < 0)
+ if (err < 0) {
+ kfree(new_frames);
return err;
+ }
if (msg_head->flags & TX_CP_CAN_ID) {
/* copy can_id into frame */
cf->can_id = msg_head->can_id;
}
}
+
+ spin_lock_bh(&op->bcm_tx_lock);
+
+ /* update CAN frames content */
+ memcpy(op->frames, new_frames, msg_head->nframes * op->cfsiz);
+
op->flags = msg_head->flags;
- /* only lock for unlikely count/nframes/currframe changes */
if (op->nframes != msg_head->nframes ||
- op->flags & TX_RESET_MULTI_IDX ||
- op->flags & SETTIMER) {
-
- spin_lock_bh(&op->bcm_tx_lock);
+ op->flags & TX_RESET_MULTI_IDX) {
+ /* potentially update changed nframes */
+ op->nframes = msg_head->nframes;
+ /* restart multiple frame transmission */
+ op->currframe = 0;
+ }
- if (op->nframes != msg_head->nframes ||
- op->flags & TX_RESET_MULTI_IDX) {
- /* potentially update changed nframes */
- op->nframes = msg_head->nframes;
- /* restart multiple frame transmission */
- op->currframe = 0;
- }
+ if (op->flags & SETTIMER)
+ op->count = msg_head->count;
- if (op->flags & SETTIMER)
- op->count = msg_head->count;
+ spin_unlock_bh(&op->bcm_tx_lock);
- spin_unlock_bh(&op->bcm_tx_lock);
- }
+ kfree(new_frames);
} else {
/* insert new BCM operation for the given can_id */
op = kzalloc(OPSIZ, GFP_KERNEL);
@@ -1154,14 +1185,16 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
} /* if ((op = bcm_find_op(&bo->tx_ops, msg_head->can_id, ifindex))) */
if (op->flags & SETTIMER) {
/* set timer values */
+ spin_lock_bh(&op->bcm_tx_lock);
op->ival1 = msg_head->ival1;
op->ival2 = msg_head->ival2;
op->kt_ival1 = bcm_timeval_to_ktime(msg_head->ival1);
op->kt_ival2 = bcm_timeval_to_ktime(msg_head->ival2);
+ spin_unlock_bh(&op->bcm_tx_lock);
/* disable an active timer due to zero values? */
if (!op->kt_ival1 && !op->kt_ival2)
hrtimer_cancel(&op->timer);
}
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread* [PATCH v9 07/10] can: bcm: validate frame length in bcm_rx_setup() for RTR replies
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
` (5 preceding siblings ...)
2026-07-09 8:16 ` [PATCH v9 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:16 ` [PATCH v9 08/10] can: bcm: add missing device refcount for CAN filter removal Oliver Hartkopp via B4 Relay
` (2 subsequent siblings)
9 siblings, 0 replies; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde
From: Oliver Hartkopp <socketcan@hartkopp.net>
bcm_tx_setup() validates cf->len against the CAN/CAN FD DLC limits
before installing frames for TX_SETUP, but bcm_rx_setup() never did
the same for the RTR-reply frame configured via RX_SETUP with
RX_RTR_FRAME.
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 59 +++++++++++++++++++++++++++++++++++++++++------------------
1 file changed, 41 insertions(+), 18 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index de4ce01bdd04..6668c1c25d92 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1222,26 +1222,41 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
kfree(op->frames);
kfree(op);
return err;
}
-static void bcm_rx_setup_rtr_check(struct bcm_msg_head *msg_head,
- struct bcm_op *op, void *new_frames)
+static int bcm_rx_setup_rtr_check(struct bcm_msg_head *msg_head,
+ struct bcm_op *op, void *new_frames)
{
+ struct canfd_frame *frame0 = new_frames;
+
+ if (!(msg_head->flags & RX_RTR_FRAME))
+ return 0;
+
+ /* this frame is sent out as-is by bcm_can_tx() whenever a matching
+ * remote request is received, so validate its length the same way
+ * bcm_tx_setup() validates TX_SETUP frames before installing it
+ */
+ if (msg_head->flags & CAN_FD_FRAME) {
+ if (frame0->len > 64)
+ return -EINVAL;
+ } else {
+ if (frame0->len > 8)
+ return -EINVAL;
+ }
+
/* funny feature in RX(!)_SETUP only for RTR-mode:
* copy can_id into frame BUT without RTR-flag to
* prevent a full-load-loopback-test ... ;-]
* normalize this on the staged buffer, before it is
* ever installed into op->frames.
*/
- if (msg_head->flags & RX_RTR_FRAME) {
- struct canfd_frame *frame0 = new_frames;
+ if ((msg_head->flags & TX_CP_CAN_ID) ||
+ frame0->can_id == op->can_id)
+ frame0->can_id = op->can_id & ~CAN_RTR_FLAG;
- if ((msg_head->flags & TX_CP_CAN_ID) ||
- frame0->can_id == op->can_id)
- frame0->can_id = op->can_id & ~CAN_RTR_FLAG;
- }
+ return 0;
}
/*
* bcm_rx_setup - create or update a bcm rx op (for bcm_sendmsg)
*/
@@ -1300,11 +1315,15 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
if (err < 0) {
kfree(new_frames);
return err;
}
- bcm_rx_setup_rtr_check(msg_head, op, new_frames);
+ err = bcm_rx_setup_rtr_check(msg_head, op, new_frames);
+ if (err < 0) {
+ kfree(new_frames);
+ return err;
+ }
}
spin_lock_bh(&op->bcm_rx_update_lock);
op->nframes = msg_head->nframes;
op->flags = msg_head->flags;
@@ -1365,20 +1384,16 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
}
if (msg_head->nframes) {
err = memcpy_from_msg(op->frames, msg,
msg_head->nframes * op->cfsiz);
- if (err < 0) {
- if (op->frames != &op->sframe)
- kfree(op->frames);
- if (op->last_frames != &op->last_sframe)
- kfree(op->last_frames);
- kfree(op);
- return err;
- }
+ if (err < 0)
+ goto free_op;
- bcm_rx_setup_rtr_check(msg_head, op, op->frames);
+ err = bcm_rx_setup_rtr_check(msg_head, op, op->frames);
+ if (err < 0)
+ goto free_op;
}
/* bcm_can_tx / bcm_tx_timeout_handler needs this */
op->sk = sk;
sock_hold(sk);
@@ -1471,10 +1486,18 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
/* add this bcm_op to the list of the rx_ops */
list_add_rcu(&op->list, &bo->rx_ops);
}
return msg_head->nframes * op->cfsiz + MHSIZ;
+
+free_op:
+ if (op->frames != &op->sframe)
+ kfree(op->frames);
+ if (op->last_frames != &op->last_sframe)
+ kfree(op->last_frames);
+ kfree(op);
+ return err;
}
/*
* bcm_tx_send - send a single CAN frame to the CAN interface (for bcm_sendmsg)
*/
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread* [PATCH v9 08/10] can: bcm: add missing device refcount for CAN filter removal
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
` (6 preceding siblings ...)
2026-07-09 8:16 ` [PATCH v9 07/10] can: bcm: validate frame length in bcm_rx_setup() for RTR replies Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:39 ` sashiko-bot
2026-07-09 8:16 ` [PATCH v9 09/10] can: bcm: fix stale rx/tx ops after device removal Oliver Hartkopp via B4 Relay
2026-07-09 8:16 ` [PATCH v9 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() Oliver Hartkopp via B4 Relay
9 siblings, 1 reply; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde, sashiko-bot
From: Oliver Hartkopp <socketcan@hartkopp.net>
sashiko-bot remarked a problem with a concurrent device unregistration
in isotp.c which also is present in the bcm.c code. A former fix for raw.c
commit c275a176e4b6 ("can: raw: add missing refcount for memory leak fix")
introduced a netdevice_tracker which solves the issue for bcm.c too.
bcm_release(), bcm_delete_rx_op() and bcm_notifier() relied on
dev_get_by_index(ifindex) to re-find the device for an rx_op before
unregistering its filter. If a concurrent NETDEV_UNREGISTER has already
unlisted the device from the ifindex table, that lookup fails and
can_rx_unregister() is silently skipped, leaving a stale CAN filter
pointing at the soon-to-be-freed bcm_op/socket.
Hold a netdev_hold()/netdev_put() tracked reference on op->rx_reg_dev
from the moment the rx filter is registered in bcm_rx_setup() until it
is unregistered in bcm_rx_unreg(), and use that reference directly in
bcm_release() and bcm_delete_rx_op() instead of re-looking the device
up by ifindex.
Reported-by: sashiko-bot@kernel.org
Link: https://sashiko.dev/#/patchset/20260707094716.63578-1-socketcan@hartkopp.net
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 47 +++++++++++++++++++++++++++--------------------
1 file changed, 27 insertions(+), 20 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index 6668c1c25d92..61725c20f087 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -126,10 +126,11 @@ struct bcm_op {
void *last_frames;
struct canfd_frame sframe;
struct canfd_frame last_sframe;
struct sock *sk;
struct net_device *rx_reg_dev;
+ netdevice_tracker rx_reg_dev_tracker;
spinlock_t bcm_tx_lock; /* protect tx data and timer updates */
spinlock_t bcm_rx_update_lock; /* protect filter/timer data updates */
};
struct bcm_sock {
@@ -913,10 +914,11 @@ static void bcm_rx_unreg(struct net_device *dev, struct bcm_op *op)
can_rx_unregister(dev_net(dev), dev, op->can_id,
REGMASK(op->can_id), bcm_rx_handler, op);
/* mark as removed subscription */
op->rx_reg_dev = NULL;
+ netdev_put(dev, &op->rx_reg_dev_tracker);
} else
printk(KERN_ERR "can-bcm: bcm_rx_unreg: registered device "
"mismatch %p %p\n", op->rx_reg_dev, dev);
}
@@ -943,21 +945,18 @@ static int bcm_delete_rx_op(struct list_head *ops, struct bcm_msg_head *mh,
if (op->ifindex) {
/*
* Only remove subscriptions that had not
* been removed due to NETDEV_UNREGISTER
* in bcm_notifier()
+ *
+ * op->rx_reg_dev is a tracked reference taken
+ * when the subscription was registered, so it
+ * stays valid here even if a concurrent
+ * NETDEV_UNREGISTER already unlisted the dev.
*/
- if (op->rx_reg_dev) {
- struct net_device *dev;
-
- dev = dev_get_by_index(sock_net(op->sk),
- op->ifindex);
- if (dev) {
- bcm_rx_unreg(dev, op);
- dev_put(dev);
- }
- }
+ if (op->rx_reg_dev)
+ bcm_rx_unreg(op->rx_reg_dev, op);
} else
can_rx_unregister(sock_net(op->sk), NULL,
op->can_id,
REGMASK(op->can_id),
bcm_rx_handler, op);
@@ -1462,11 +1461,21 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
op->can_id,
REGMASK(op->can_id),
bcm_rx_handler, op,
"bcm", sk);
- op->rx_reg_dev = dev;
+ /* keep a tracked reference so that a later
+ * unregister can safely reach the device even
+ * if a concurrent NETDEV_UNREGISTER has
+ * already unlisted it by ifindex
+ */
+ if (!err) {
+ op->rx_reg_dev = dev;
+ netdev_hold(dev,
+ &op->rx_reg_dev_tracker,
+ GFP_KERNEL);
+ }
dev_put(dev);
} else {
/* the requested device is gone - do not
* silently succeed without registering
*/
@@ -1839,20 +1848,18 @@ static int bcm_release(struct socket *sock)
if (op->ifindex) {
/*
* Only remove subscriptions that had not
* been removed due to NETDEV_UNREGISTER
* in bcm_notifier()
+ *
+ * op->rx_reg_dev is a tracked reference taken
+ * when the subscription was registered, so it
+ * stays valid here even if a concurrent
+ * NETDEV_UNREGISTER already unlisted the device.
*/
- if (op->rx_reg_dev) {
- struct net_device *dev;
-
- dev = dev_get_by_index(net, op->ifindex);
- if (dev) {
- bcm_rx_unreg(dev, op);
- dev_put(dev);
- }
- }
+ if (op->rx_reg_dev)
+ bcm_rx_unreg(op->rx_reg_dev, op);
} else
can_rx_unregister(net, NULL, op->can_id,
REGMASK(op->can_id),
bcm_rx_handler, op);
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread* Re: [PATCH v9 08/10] can: bcm: add missing device refcount for CAN filter removal
2026-07-09 8:16 ` [PATCH v9 08/10] can: bcm: add missing device refcount for CAN filter removal Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:39 ` sashiko-bot
0 siblings, 0 replies; 16+ messages in thread
From: sashiko-bot @ 2026-07-09 8:39 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Oleksij Rempel, linux-can, Oliver Hartkopp, Vincent Mailhol,
Marc Kleine-Budde
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues:
- [High] An existing BCM RX filter silently fails to re-register if its bound device is unregistered and later replaced, or if the socket is bound to 'any' interface and the device is recreated.
--
--- Patch [8]: [PATCH v9 08/10] can: bcm: add missing device refcount for CAN filter removal ---
commit 1ad23d1877e2e80147338573cbaebed867d37fc0
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: add missing device refcount for CAN filter removal
This commit fixes a missing device refcount issue in bcm.c when unregistering
a CAN filter. It introduces a netdevice_tracker to hold a reference on
op->rx_reg_dev from filter registration until unregistration, preventing
lookups on a stale device index.
Link: https://sashiko.dev/#/patchset/20260707094716.63578-1-socketcan@hartkopp.net
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index 6668c1c25d923..61725c20f087e 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
[ ... ]
> @@ -1464,7 +1463,17 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
> bcm_rx_handler, op,
> "bcm", sk);
>
> - op->rx_reg_dev = dev;
[Severity: High]
This isn't a bug introduced by this patch, but is there a scenario where an
existing BCM RX filter silently fails to re-register?
If a BCM socket is bound to interface 0, an RX_SETUP creates an operation
for a specific interface and sets op->rx_reg_dev. If that interface is then
unregistered, bcm_notify() unregisters the filter and clears op->rx_reg_dev
but leaves the operation in bo->rx_ops.
When the device is recreated and another RX_SETUP is sent for the same id
and ifindex, bcm_find_op() in bcm_rx_setup() finds the existing operation.
Because it is found, do_rx_register remains 0. The setup then returns
success but bypasses the can_rx_register() phase entirely.
Does this sequence result in the filter remaining inactive on the newly
created device and silently dropping expected CAN frames?
> + /* keep a tracked reference so that a later
> + * unregister can safely reach the device even
> + * if a concurrent NETDEV_UNREGISTER has
> + * already unlisted it by ifindex
> + */
> + if (!err) {
> + op->rx_reg_dev = dev;
> + netdev_hold(dev,
> + &op->rx_reg_dev_tracker,
> + GFP_KERNEL);
> + }
> dev_put(dev);
> } else {
> /* the requested device is gone - do not
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v9-0-6eebb78ccfb2@hartkopp.net?part=8
^ permalink raw reply [flat|nested] 16+ messages in thread
* [PATCH v9 09/10] can: bcm: fix stale rx/tx ops after device removal
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
` (7 preceding siblings ...)
2026-07-09 8:16 ` [PATCH v9 08/10] can: bcm: add missing device refcount for CAN filter removal Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
2026-07-09 8:16 ` [PATCH v9 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() Oliver Hartkopp via B4 Relay
9 siblings, 0 replies; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde, sashiko-bot
From: Oliver Hartkopp <socketcan@hartkopp.net>
RX: an RX_SETUP update(!) for an existing op skipped can_rx_register()
unconditionally, even when a concurrent NETDEV_UNREGISTER had already
torn down its registration (op->rx_reg_dev == NULL). This silently
did not re-enable frame delivery for that updated filter. bcm_rx_setup()
now re-registers in that case, while leaving rx_ops with ifindex = 0
(all CAN devices) which never carry a tracked rx_reg_dev registered as-is.
TX: bcm_notify() only handled bo->rx_ops on NETDEV_UNREGISTER, leaving
tx_ops with an active cyclic transmission re-arming its hrtimer
indefinitely to execute bcm_tx_timeout_handler(). Cancelling the hrtimer
prevents the runaway timer and any injection into a later reused ifindex,
since nothing else calls bcm_can_tx() for the op until an explicit
TX_SETUP update re-arms it.
Unlike bcm_rx_unreg(), which clears the tracked rx_reg_dev for rx_ops,
the ifindex is intentionally left unchanged for tx_ops. bcm_tx_setup()
always rejects ifindex 0, so clearing it would strand the op: neither a
later TX_SETUP (bcm_find_op()) nor TX_DELETE (bcm_delete_tx_op()) could
ever find it again, since both require an exact ifindex match.
Reported-by: sashiko-bot@kernel.org
Link: https://lore.kernel.org/linux-can/20260708094536.DDF821F00A3A@smtp.kernel.org/
Link: https://lore.kernel.org/linux-can/20260708154039.347ED1F000E9@smtp.kernel.org/
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 47 ++++++++++++++++++++++++++++++++++++++---------
1 file changed, 38 insertions(+), 9 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index 61725c20f087..19e10b0d729b 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1263,10 +1263,11 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
int ifindex, struct sock *sk)
{
struct bcm_sock *bo = bcm_sk(sk);
struct bcm_op *op;
int do_rx_register;
+ int new_op = 0;
int err = 0;
if ((msg_head->flags & RX_FILTER_ID) || (!(msg_head->nframes))) {
/* be robust against wrong usage ... */
msg_head->flags |= RX_FILTER_ID;
@@ -1339,12 +1340,19 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
spin_unlock_bh(&op->bcm_rx_update_lock);
/* free temporary frames / kfree(NULL) is safe */
kfree(new_frames);
- /* Only an update -> do not call can_rx_register() */
- do_rx_register = 0;
+ /* Don't register a new CAN filter for the rx_op update unless
+ * a concurrent NETDEV_UNREGISTER notifier already tore down
+ * the previous registration. In this case the receiver needs
+ * to be re-registered here so that this update doesn't
+ * silently stop delivering frames for the given ifindex.
+ * Ops with ifindex = 0 (all CAN interfaces) never carry a
+ * tracked rx_reg_dev and stay registered as-is.
+ */
+ do_rx_register = (ifindex && !op->rx_reg_dev) ? 1 : 0;
} else {
/* insert new BCM operation for the given can_id */
op = kzalloc(OPSIZ, GFP_KERNEL);
if (!op)
@@ -1407,10 +1415,11 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
hrtimer_setup(&op->thrtimer, bcm_rx_thr_handler, CLOCK_MONOTONIC,
HRTIMER_MODE_REL_SOFT);
/* call can_rx_register() */
do_rx_register = 1;
+ new_op = 1;
} /* if ((op = bcm_find_op(&bo->rx_ops, msg_head->can_id, ifindex))) */
/* check flags */
@@ -1448,11 +1457,14 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
if ((op->flags & STARTTIMER) && op->kt_ival1)
hrtimer_start(&op->timer, op->kt_ival1,
HRTIMER_MODE_REL_SOFT);
}
- /* now we can register for can_ids, if we added a new bcm_op */
+ /* now we can register for can_ids, if we added a new bcm_op
+ * or need to re-register after a NETDEV_UNREGISTER tore down
+ * the previous registration of an existing op
+ */
if (do_rx_register) {
if (ifindex) {
struct net_device *dev;
dev = dev_get_by_index(sock_net(sk), ifindex);
@@ -1480,22 +1492,31 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
* silently succeed without registering
*/
err = -ENODEV;
}
- } else
+ } else {
err = can_rx_register(sock_net(sk), NULL, op->can_id,
REGMASK(op->can_id),
bcm_rx_handler, op, "bcm", sk);
+ }
+
if (err) {
- /* this bcm rx op is broken -> remove it */
- bcm_remove_op(op);
+ /* newly created bcm rx op is broken -> remove it */
+ if (new_op)
+ bcm_remove_op(op);
+
+ /* an existing op just stays unregistered until the
+ * next successful RX_SETUP - it is already part of
+ * bo->rx_ops and must not be freed here
+ */
return err;
}
- /* add this bcm_op to the list of the rx_ops */
- list_add_rcu(&op->list, &bo->rx_ops);
+ /* add a new bcm_op to the list of the rx_ops */
+ if (new_op)
+ list_add_rcu(&op->list, &bo->rx_ops);
}
return msg_head->nframes * op->cfsiz + MHSIZ;
free_op:
@@ -1711,15 +1732,23 @@ static void bcm_notify(struct bcm_sock *bo, unsigned long msg,
switch (msg) {
case NETDEV_UNREGISTER:
lock_sock(sk);
- /* remove device specific receive entries */
+ /* rx_ops: remove device specific receive entries */
list_for_each_entry(op, &bo->rx_ops, list)
if (op->rx_reg_dev == dev)
bcm_rx_unreg(dev, op);
+ /* tx_ops: stop device specific cyclic transmissions on the
+ * vanishing ifindex. Cancelling the timer is enough to stop
+ * cyclic bcm_can_tx() calls as there is no re-arming.
+ */
+ list_for_each_entry(op, &bo->tx_ops, list)
+ if (op->ifindex == dev->ifindex)
+ hrtimer_cancel(&op->timer);
+
/* remove device reference, if this is our bound device */
if (bo->bound && bo->ifindex == dev->ifindex) {
#if IS_ENABLED(CONFIG_PROC_FS)
if (sock_net(sk)->can.bcmproc_dir && bo->bcm_proc_read) {
remove_proc_entry(bo->procname, sock_net(sk)->can.bcmproc_dir);
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread* [PATCH v9 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
2026-07-09 8:16 [PATCH v9 00/10] can: bcm: collected fixes - final4 :-O Oliver Hartkopp via B4 Relay
` (8 preceding siblings ...)
2026-07-09 8:16 ` [PATCH v9 09/10] can: bcm: fix stale rx/tx ops after device removal Oliver Hartkopp via B4 Relay
@ 2026-07-09 8:16 ` Oliver Hartkopp via B4 Relay
9 siblings, 0 replies; 16+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 8:16 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde, sashiko-bot
From: Oliver Hartkopp <socketcan@hartkopp.net>
For an rx op subscribed on all interfaces (ifindex == 0), the same op
is registered once in the shared per-netns wildcard filter list, so
bcm_rx_handler() can run concurrently on different CPUs for frames
arriving on different net devices.
op->rx_stamp and op->rx_ifindex were written before bcm_rx_update_lock was
taken, allowing concurrent writers to race each other - including a torn
store of the 64-bit rx_stamp on 32-bit platforms.
Beyond a torn store bcm_send_to_user() must report the timestamp/ifindex
of the very same frame whose content it is delivering. So the assignment
is placed in the same unbroken bcm_rx_update_lock section as the content
comparison.
As a side effect, the RTR-request frame feature (which never reach
bcm_send_to_user()) no longer updates rx_stamp/rx_ifindex, since only
the notification path needs them.
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Reported-by: sashiko-bot@kernel.org
Link: https://lore.kernel.org/linux-can/20260707145135.5BC831F00A3A@smtp.kernel.org/
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index 19e10b0d729b..4bdae37781bc 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -777,15 +777,10 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
}
/* disable timeout */
hrtimer_cancel(&op->timer);
- /* save rx timestamp */
- op->rx_stamp = skb->tstamp;
- /* save originator for recvfrom() */
- op->rx_ifindex = skb->dev->ifindex;
-
/* snapshot RTR content under lock: op->flags/op->frames may be
* updated concurrently by bcm_rx_setup().
*/
spin_lock_bh(&op->bcm_rx_update_lock);
@@ -812,10 +807,18 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
traffic_flags |= RX_OWN;
}
spin_lock_bh(&op->bcm_rx_update_lock);
+ /* save rx timestamp and originator for recvfrom() under lock.
+ * For an op subscribed on all interfaces (ifindex == 0)
+ * bcm_rx_handler() can run concurrently on different CPUs so
+ * the CAN content and the meta data must be bundled correctly.
+ */
+ op->rx_stamp = skb->tstamp;
+ op->rx_ifindex = skb->dev->ifindex;
+
if (op->flags & RX_FILTER_ID) {
/* the easiest case */
bcm_rx_update_and_send(op, op->last_frames, rxframe,
traffic_flags);
goto rx_starttimer;
--
2.53.0
^ permalink raw reply related [flat|nested] 16+ messages in thread