* [PATCH v8 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:26 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:43 ` sashiko-bot
2026-07-08 17:26 ` [PATCH v8 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
` (9 subsequent siblings)
10 siblings, 1 reply; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:26 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] 19+ messages in thread* Re: [PATCH v8 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
2026-07-08 17:26 ` [PATCH v8 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:43 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-08 17:43 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: linux-can, Vincent Mailhol, Oliver Hartkopp, Marc Kleine-Budde,
Oleksij Rempel
Thank you for your contribution! Sashiko AI review found 5 potential issue(s) to consider:
Pre-existing issues:
- [High] Data race and potential memory corruption when updating an existing RX operation's filter frames.
- [High] Unsafe lockless iteration over `bo->tx_ops` in procfs handler.
- [High] TOCTOU data race allowing transmission of unvalidated cf->len, leading to Information Leak.
- [High] Missing validation of cf->len for RX_SETUP messages allows OOB read on RTR replies.
- [High] Unbounded kernel memory allocation in TX_SETUP and RX_SETUP enables local DoS.
--
--- Patch [1]: [PATCH v8 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF ---
commit 57a8040fac83846a436e2754c21b148f177f0ef3
Author: Lee Jones <lee@kernel.org>
can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
This patch defers the teardown and memory deallocation of bcm_op structures
to a dedicated workqueue. This prevents use-after-free issues caused by
timers firing after RCU grace periods, and avoids sleeping in softirq
context. It also adds socket reference counting during the deferred work.
> 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
[ ... ]
> @@ -1060,6 +1081,7 @@ 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 */
[Severity: High]
This is a pre-existing issue, but is there an unsafe lockless iteration
over bo->tx_ops in the procfs handler?
In bcm_tx_setup(), elements are added to the bo->tx_ops list using
list_add(), which lacks the memory barriers of list_add_rcu(). However,
bcm_proc_show() iterates this list using list_for_each_entry() while only
holding rcu_read_lock().
If a user continuously creates TX operations while concurrently reading the
socket's procfs file, could the procfs reader observe an uninitialized next
pointer and cause a crash due to an invalid pointer dereference?
[Severity: High]
This isn't a bug introduced by this patch, but does bcm_tx_setup() contain
a time-of-check to time-of-use (TOCTOU) data race?
If a user updates an existing TX operation while its cyclic timer is firing,
bcm_tx_setup() directly modifies op->frames with user-supplied data before
validating it:
bcm_tx_setup()
err = memcpy_from_msg((u8 *)cf, msg, op->cfsiz);
if (op->flags & CAN_FD_FRAME) {
if (cf->len > 64)
err = -EINVAL;
If the timer concurrently triggers bcm_tx_timeout_handler(), which calls
bcm_can_tx(), it can copy the partially updated frame into an SKB. Could
the CAN driver then read past the SKB data bounds based on an unvalidated
cf->len, leading to an out-of-bounds read and information leak?
[Severity: High]
This isn't a bug introduced by this patch, but do the allocations in
bcm_tx_setup() and bcm_rx_setup() lack memory limits?
A local user can open a CAN_BCM socket (which doesn't require
CAP_NET_ADMIN) and loop sendmsg() with TX_SETUP or RX_SETUP opcodes
using unique CAN IDs.
Since these functions allocate large structures and frame arrays using
kzalloc() and kmalloc_array() without charging the memory against the
socket's limits (for example, via sk_mem_charge()), could an attacker
exhaust kernel memory and cause a local denial of service?
[ ... ]
> @@ -1221,6 +1243,7 @@ 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 */
[Severity: High]
This isn't a bug introduced by this patch, but there is a data race when
updating an existing RX operation's filter frames.
When a user updates an existing RX filter via bcm_sendmsg(), bcm_rx_setup()
copies data directly into op->frames using memcpy_from_msg() and clears
op->last_frames via memset() without holding a lock.
Concurrently, can a packet reception trigger bcm_rx_handler() in softirq
context, causing it to read these arrays locklessly and observe torn or
zeroed state?
[Severity: High]
This is a pre-existing issue, but it looks like bcm_rx_setup() is missing
length validation for the supplied RX configuration frames.
When a user configures an RX operation with the RX_RTR_FRAME flag and
supplies a frame with a large cf->len, bcm_rx_setup() copies it via
memcpy_from_msg() but fails to validate the length.
When a matching RTR request is received, bcm_rx_handler() invokes
bcm_can_tx() to reply. Could the CAN driver then blindly trust cf->len
and read out of bounds on the SKB buffer, exposing adjacent kernel heap
memory on the CAN bus?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260708-bcm_fixes-v8-0-8c2f5f3bc212@hartkopp.net?part=1
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v8 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
2026-07-08 17:26 ` [PATCH v8 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:26 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:43 ` sashiko-bot
2026-07-08 17:27 ` [PATCH v8 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
` (8 subsequent siblings)
10 siblings, 1 reply; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:26 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] 19+ messages in thread* Re: [PATCH v8 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
2026-07-08 17:26 ` [PATCH v8 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:43 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-08 17:43 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Oliver Hartkopp, Vincent Mailhol, Marc Kleine-Budde,
Oleksij Rempel, linux-can
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues:
- [Critical] Data race between lockless /proc readers and socket list modification due to missing RCU protections.
--
--- Patch [2]: [PATCH v8 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure ---
commit 2478889b563324c073bf7ec2b2aeeb796709e2ce
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
The patch fixes a race condition where lockless reads of bo->bound and
bo->ifindex could tear against concurrent locked updates. It also fixes a
silent failure in bcm_rx_setup() when the target device disappears.
Link: 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
> index bdf53241bd7b3..b612135b017d1 100644
> --- 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: Critical]
This is a pre-existing issue, but does this code have a data race between
lockless /proc readers and socket list modifications?
In bcm_proc_show(), bo->rx_ops and bo->tx_ops are traversed locklessly under
rcu_read_lock(). However, bcm_rx_setup() and bcm_tx_setup() use the non-RCU
list_add() function to insert elements, omitting the required 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);
...
}
net/can/bcm.c:bcm_tx_setup() {
...
/* add this bcm_op to the list of the tx_ops */
list_add(&op->list, &bo->tx_ops);
...
}
Additionally, while rx_ops is traversed with list_for_each_entry_rcu(), tx_ops
is traversed without RCU primitives entirely:
net/can/bcm.c:bcm_proc_show() {
...
rcu_read_lock();
list_for_each_entry_rcu(op, &bo->rx_ops, list) {
...
list_for_each_entry(op, &bo->tx_ops, list) {
...
}
Can an unprivileged local user trigger a kernel panic by opening the
/proc/net/can-bcm/<inode> file while concurrently adding operations via
RX_SETUP or TX_SETUP? Should list_add_rcu() and list_for_each_entry_rcu() be
used instead to ensure list integrity?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260708-bcm_fixes-v8-0-8c2f5f3bc212@hartkopp.net?part=2
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v8 03/10] can: bcm: add locking when updating filter and timer values
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
2026-07-08 17:26 ` [PATCH v8 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
2026-07-08 17:26 ` [PATCH v8 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:27 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:44 ` sashiko-bot
2026-07-08 17:27 ` [PATCH v8 04/10] can: bcm: fix CAN frame rx/tx statistics Oliver Hartkopp via B4 Relay
` (7 subsequent siblings)
10 siblings, 1 reply; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:27 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] 19+ messages in thread* Re: [PATCH v8 03/10] can: bcm: add locking when updating filter and timer values
2026-07-08 17:27 ` [PATCH v8 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:44 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-08 17:44 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Vincent Mailhol, linux-can, Marc Kleine-Budde, Oliver Hartkopp,
Oleksij Rempel
Thank you for your contribution! Sashiko AI review found 6 potential issue(s) to consider:
Pre-existing issues:
- [High] Torn read data races on timer values in the TX path.
- [High] The lock added in bcm_can_tx() is ineffective against torn reads because the writer (bcm_tx_setup) does not hold the lock.
- [High] Timer armed on freed bcm_op due to race between bcm_rx_handler and bcm_delete_rx_op.
- [High] Missing list_add_rcu() for BCM operations accessed locklessly via RCU.
- [High] Unsafe lockless traversal of tx_ops list in procfs handler.
- [Medium] op->rx_stamp, op->rx_ifindex, and op->frames_abs are updated locklessly in bcm_rx_handler().
--
--- Patch [3]: [PATCH v8 03/10] can: bcm: add locking when updating filter and timer values ---
commit ae43444642bccb605ce6673ee360da9626ce6a3b
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: add locking when updating filter and timer values
This commit adds a new bcm_rx_update_lock to protect timer and filter data
updates in bcm_rx_setup() against concurrent execution of RX handlers.
It also modifies the transmit paths and timer handlers to attempt to close
several synchronization races.
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
[ ... ]
> -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;
[ ... ]
> + 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);
> + }
[Severity: High]
This isn't a bug introduced by this patch, but is this lock effective
against torn reads here?
The writer in bcm_tx_setup() modifies op->frames locklessly via
memcpy_from_msg():
bcm_tx_setup()
err = memcpy_from_msg((u8 *)cf, msg, op->cfsiz);
Since the writer mutates the buffer without holding bcm_tx_lock, does the
reader's lock in bcm_can_tx() prevent a concurrently firing timer callback
from reading and transmitting a corrupted, partially-overwritten CAN frame?
[ ... ]
> @@ -461,7 +466,7 @@ static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
> struct bcm_msg_head msg_head;
>
> if (op->kt_ival1 && (op->count > 0)) {
> - bcm_can_tx(op);
> + bcm_can_tx(op, NULL);
[Severity: High]
This is a pre-existing issue, but can we experience torn reads on these
timer values?
In bcm_tx_setup(), the timer fields are updated locklessly:
bcm_tx_setup()
op->kt_ival1 = bcm_timeval_to_ktime(msg_head->ival1);
op->kt_ival2 = bcm_timeval_to_ktime(msg_head->ival2);
Concurrently, bcm_tx_timeout_handler() and bcm_tx_set_expiry() read these
fields locklessly.
On 32-bit systems, reading or writing a 64-bit ktime_t is not atomic.
Could a torn read (where half of the old ktime and half of the new one
are read) result in a corrupted timer expiration time being programmed?
[ ... ]
> @@ -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 isn't a bug introduced by this patch, but does the lockless update of
metadata before taking bcm_rx_update_lock cause mismatched data?
Right before this snippet, bcm_rx_handler() updates metadata locklessly:
bcm_rx_handler()
op->rx_stamp = skb->tstamp;
op->rx_ifindex = skb->dev->ifindex;
op->frames_abs++;
For a socket bound to all interfaces (ifindex == 0), bcm_rx_handler() can
execute concurrently on multiple CPUs for the same bcm_op.
Since bcm_send_to_user() reads these values inside the lock, could it bundle
a CAN frame from one CPU with the timestamp or ifindex metadata from another?
[ ... ]
> @@ -778,6 +811,8 @@ 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);
> }
[Severity: High]
This is a pre-existing issue, but can this arm the timer on a freed object?
The teardown path in bcm_delete_rx_op() sets the flag locklessly and
cancels the timer:
bcm_delete_rx_op()
op->flags |= RX_NO_AUTOTIMER;
...
hrtimer_cancel(&op->timer);
Since bcm_delete_rx_op() doesn't take bcm_rx_update_lock, it can cancel
the timer before the handler arms it.
If bcm_rx_handler() reads op->flags before it is set, and then reaches
bcm_rx_starttimer(), could it start the timer on an object that will be
freed after the RCU grace period, causing a use-after-free?
[ ... ]
> @@ -1116,7 +1151,7 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
> }
>
> if (op->flags & TX_ANNOUNCE)
> - bcm_can_tx(op);
> + bcm_can_tx(op, NULL);
[Severity: High]
This is a pre-existing issue, but is the lockless traversal of tx_ops safe?
bcm_tx_setup() adds operations to the list using list_add():
bcm_tx_setup()
list_add(&op->list, &bo->tx_ops);
However, bcm_proc_show() iterates this list locklessly using the non-RCU
macro list_for_each_entry() while holding only rcu_read_lock().
Since the procfs reader does not use the proper RCU primitives for tx_ops,
could it follow corrupted pointers if the list is modified concurrently?
[ ... ]
> @@ -1164,6 +1217,8 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
> /* check the given can_id */
> op = bcm_find_op(&bo->rx_ops, msg_head, ifindex);
> if (op) {
> + void *new_frames = NULL;
> +
[Severity: High]
This is a pre-existing issue, but does rx_ops require list_add_rcu()?
Later in bcm_rx_setup(), it inserts the struct into the rx_ops list without
RCU memory barriers:
bcm_rx_setup()
list_add(&op->list, &bo->rx_ops);
Meanwhile, bcm_proc_show() iterates the list expecting RCU protection:
bcm_proc_show()
list_for_each_entry_rcu(op, &bo->rx_ops, list) { ... }
Because list_add() lacks the smp_store_release() semantics of
list_add_rcu(), could an RCU reader observe the new list node before its
memory contents are fully visible across cores?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260708-bcm_fixes-v8-0-8c2f5f3bc212@hartkopp.net?part=3
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v8 04/10] can: bcm: fix CAN frame rx/tx statistics
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
` (2 preceding siblings ...)
2026-07-08 17:27 ` [PATCH v8 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:27 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:39 ` sashiko-bot
2026-07-08 17:27 ` [PATCH v8 05/10] can: bcm: add missing rcu list annotations and operations Oliver Hartkopp via B4 Relay
` (6 subsequent siblings)
10 siblings, 1 reply; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:27 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 a separate bcm_update_stats() function and
put this function under bcm_rx_update_lock to prevent races when resetting
the counters.
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 47 ++++++++++++++++++++++++++++++-----------------
1 file changed, 30 insertions(+), 17 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index af4bb4182bc2..340b7fc89744 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 +281,30 @@ 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_stats(struct bcm_op *op)
+{
+ /* prevent statistics overflow */
+ 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);
+ }
+}
+
/*
* 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 +355,11 @@ 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_stats(op);
op->currframe++;
/* reached last frame? */
if (op->currframe >= op->nframes)
@@ -495,16 +508,13 @@ 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 +756,23 @@ 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_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] 19+ messages in thread* Re: [PATCH v8 04/10] can: bcm: fix CAN frame rx/tx statistics
2026-07-08 17:27 ` [PATCH v8 04/10] can: bcm: fix CAN frame rx/tx statistics Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:39 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-08 17:39 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Marc Kleine-Budde, Vincent Mailhol, Oleksij Rempel,
Oliver Hartkopp, linux-can
Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
New issues:
- [Medium] `bcm_update_stats()` can be executed concurrently from different lock domains, contradicting the commit's claim of preventing races during counter reset.
- [Medium] TX operations incorrectly inherit the RX-specific statistics cap, causing premature zeroing of the TX frame counter.
Pre-existing issues:
- [High] Unprotected modifications of `op->rx_stamp` and `op->rx_ifindex` in `bcm_rx_handler()` lead to data races and torn writes of 64-bit metadata.
--
--- Patch [4]: [PATCH v8 04/10] can: bcm: fix CAN frame rx/tx statistics ---
commit 7e13c48f66a83858015c68aa3f0ac7aba6688936
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: fix CAN frame rx/tx statistics
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. Additionally simplify the update and check of
statistics overflow by using the atomic operations in a separate
bcm_update_stats() function and put this function under bcm_rx_update_lock
to prevent races when resetting the counters.
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index af4bb4182bc29..340b7fc89744e 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
[ ... ]
> @@ -344,7 +357,7 @@ 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_stats(op);
[Severity: Medium]
Does this inadvertently inherit the RX-specific limit for the TX path?
TX operations don't use frames_filtered or calculate a reduction percentage,
so the LONG_MAX / 100 limit enforced inside bcm_update_stats() seems logically
unnecessary here. On 32-bit systems, does this artificially cap the TX sent
counter to 21.4 million frames before abruptly resetting to zero, whereas
prior to this patch it safely counted up to ULONG_MAX?
[Severity: Medium]
The commit message mentions putting bcm_update_stats() under
bcm_rx_update_lock to prevent races when resetting the counters. However,
is it possible for bcm_update_stats() to be called concurrently from
different lock domains?
If an RX operation is configured with RX_RTR_FRAME, it can receive multiple
RTR frames concurrently. bcm_rx_handler() calls bcm_update_stats() while
holding bcm_rx_update_lock. It then invokes bcm_can_tx() to send the reply,
which calls bcm_update_stats() right here while holding a DIFFERENT lock,
bcm_tx_lock:
bcm_rx_handler()
spin_lock_bh(&op->bcm_rx_update_lock);
bcm_update_stats(op);
spin_unlock_bh(&op->bcm_rx_update_lock);
...
bcm_can_tx()
spin_lock_bh(&op->bcm_tx_lock);
bcm_update_stats(op);
Could this allow the reset logic inside bcm_update_stats() to run
concurrently across two CPUs, leading to an inconsistent counter reset?
[ ... ]
> @@ -748,16 +758,19 @@ 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;
> - /* 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);
[Severity: High]
This isn't a bug introduced by this patch, but while fixing the KCSAN data
race in bcm_rx_handler(), are op->rx_stamp and op->rx_ifindex still
vulnerable to concurrent torn writes?
These fields are written without any lock protection just before
bcm_rx_update_lock is acquired. If multiple CAN frames for the same RX
operation are received simultaneously on different CPUs, could the 64-bit
ktime_t timestamp tear on 32-bit systems? This might result in a wildly
incorrect timestamp value being passed to userspace via bcm_send_to_user()
along with misattributed network interfaces in the metadata.
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260708-bcm_fixes-v8-0-8c2f5f3bc212@hartkopp.net?part=4
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v8 05/10] can: bcm: add missing rcu list annotations and operations
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
` (3 preceding siblings ...)
2026-07-08 17:27 ` [PATCH v8 04/10] can: bcm: fix CAN frame rx/tx statistics Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:27 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:43 ` sashiko-bot
2026-07-08 17:27 ` [PATCH v8 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates Oliver Hartkopp via B4 Relay
` (5 subsequent siblings)
10 siblings, 1 reply; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:27 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 340b7fc89744..fca7c714cc52 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)
@@ -997,10 +997,11 @@ 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)
@@ -1138,12 +1139,11 @@ 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 */
@@ -1161,10 +1161,14 @@ 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);
@@ -1345,13 +1349,10 @@ 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))) */
@@ -1419,14 +1420,16 @@ 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;
}
@@ -1756,12 +1759,14 @@ 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.
@@ -1788,12 +1793,14 @@ 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] 19+ messages in thread* Re: [PATCH v8 05/10] can: bcm: add missing rcu list annotations and operations
2026-07-08 17:27 ` [PATCH v8 05/10] can: bcm: add missing rcu list annotations and operations Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:43 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-08 17:43 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Oliver Hartkopp, linux-can, Vincent Mailhol, Oleksij Rempel,
Marc Kleine-Budde
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues:
- [High] The timer callback `bcm_tx_timeout_handler()` reads `op->kt_ival1`, `op->kt_ival2`, and `op->count` locklessly, risking torn reads and inconsistent state.
--
--- Patch [5]: [PATCH v8 05/10] can: bcm: add missing rcu list annotations and operations ---
commit 328ac2042a77c92625995c774ca6b37b5d654ec7
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: add missing rcu list annotations and operations
This commit fixes missing RCU list annotations for bcm_op additions and
removals to ensure procfs safely traverses the structures under
rcu_read_lock(). It also moves list additions to the end of the setup code
and fixes the removal path in bcm_release().
Closes: https://lore.kernel.org/linux-can/20260610094654.A1FFE1F00893@smtp.kernel.org/
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index 340b7fc89744e..fca7c714cc52f 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
[ ... ]
> @@ -1163,6 +1163,10 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
> 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);
> +
[Severity: High]
This isn't a bug introduced by this patch, but while looking at the context
around bcm_tx_setup(), I noticed a potential problem with how the timer
variables are synchronized.
Although bcm_tx_setup() safely updates op->kt_ival1, op->kt_ival2, and
op->count under op->bcm_tx_lock, the timer callback bcm_tx_timeout_handler()
and bcm_tx_set_expiry() appear to read them locklessly:
net/can/bcm.c:bcm_tx_timeout_handler() {
...
if (op->kt_ival1 && (op->count > 0)) {
bcm_can_tx(op, NULL);
...
}
net/can/bcm.c:bcm_tx_set_expiry() {
...
if (op->kt_ival1 && op->count)
ival = op->kt_ival1;
else if (op->kt_ival2)
ival = op->kt_ival2;
...
}
Could this result in torn reads of the 64-bit ktime_t variables on 32-bit
platforms, or reading an inconsistent combination of count and interval
values?
If a user calls sendmsg() with SETTIMER (but without STARTTIMER) on an
active cyclic TX operation, could the already-running hrtimer execute
concurrently in softirq context and be rearmed with an incorrect
expiration time?
> if (op->flags & TX_ANNOUNCE)
> bcm_can_tx(op, NULL);
>
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260708-bcm_fixes-v8-0-8c2f5f3bc212@hartkopp.net?part=5
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v8 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
` (4 preceding siblings ...)
2026-07-08 17:27 ` [PATCH v8 05/10] can: bcm: add missing rcu list annotations and operations Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:27 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:27 ` [PATCH v8 07/10] can: bcm: validate frame length in bcm_rx_setup() for RTR replies Oliver Hartkopp via B4 Relay
` (4 subsequent siblings)
10 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:27 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 fca7c714cc52..fefa77045253 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;
@@ -453,16 +453,22 @@ 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;
}
@@ -475,12 +481,21 @@ 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));
@@ -493,11 +508,11 @@ 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;
@@ -1016,64 +1031,80 @@ 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);
@@ -1145,14 +1176,16 @@ 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] 19+ messages in thread* [PATCH v8 07/10] can: bcm: validate frame length in bcm_rx_setup() for RTR replies
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
` (5 preceding siblings ...)
2026-07-08 17:27 ` [PATCH v8 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:27 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:27 ` [PATCH v8 08/10] can: bcm: add missing device refcount for CAN filter removal Oliver Hartkopp via B4 Relay
` (3 subsequent siblings)
10 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:27 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 fefa77045253..300f1f88c4d2 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1213,26 +1213,41 @@ 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)
*/
@@ -1291,11 +1306,15 @@ 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;
@@ -1356,20 +1375,16 @@ 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);
@@ -1462,10 +1477,18 @@ 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] 19+ messages in thread* [PATCH v8 08/10] can: bcm: add missing device refcount for CAN filter removal
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
` (6 preceding siblings ...)
2026-07-08 17:27 ` [PATCH v8 07/10] can: bcm: validate frame length in bcm_rx_setup() for RTR replies Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:27 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:27 ` [PATCH v8 09/10] can: bcm: fix stale rx/tx ops after device removal Oliver Hartkopp via B4 Relay
` (2 subsequent siblings)
10 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:27 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 300f1f88c4d2..4bdca72f9327 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 {
@@ -904,10 +905,11 @@ 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);
}
@@ -934,21 +936,18 @@ 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);
@@ -1453,11 +1452,21 @@ 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
*/
@@ -1830,20 +1839,18 @@ 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] 19+ messages in thread* [PATCH v8 09/10] can: bcm: fix stale rx/tx ops after device removal
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
` (7 preceding siblings ...)
2026-07-08 17:27 ` [PATCH v8 08/10] can: bcm: add missing device refcount for CAN filter removal Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:27 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:27 ` [PATCH v8 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() Oliver Hartkopp via B4 Relay
2026-07-08 21:23 ` [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Marc Kleine-Budde
10 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:27 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 4bdca72f9327..66dd8789843b 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1254,10 +1254,11 @@ 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;
@@ -1330,12 +1331,19 @@ 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)
@@ -1398,10 +1406,11 @@ 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 */
@@ -1439,11 +1448,14 @@ 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);
@@ -1471,22 +1483,31 @@ 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:
@@ -1702,15 +1723,23 @@ 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] 19+ messages in thread* [PATCH v8 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
` (8 preceding siblings ...)
2026-07-08 17:27 ` [PATCH v8 09/10] can: bcm: fix stale rx/tx ops after device removal Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:27 ` Oliver Hartkopp via B4 Relay
2026-07-08 17:47 ` sashiko-bot
2026-07-08 21:23 ` [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Marc Kleine-Budde
10 siblings, 1 reply; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-08 17:27 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 66dd8789843b..1986d33a7d27 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -768,15 +768,10 @@ 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);
@@ -803,10 +798,18 @@ 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] 19+ messages in thread* Re: [PATCH v8 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
2026-07-08 17:27 ` [PATCH v8 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() Oliver Hartkopp via B4 Relay
@ 2026-07-08 17:47 ` sashiko-bot
2026-07-08 18:38 ` Oliver Hartkopp
0 siblings, 1 reply; 19+ messages in thread
From: sashiko-bot @ 2026-07-08 17:47 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: linux-can, Oleksij Rempel, Vincent Mailhol, Marc Kleine-Budde,
Oliver Hartkopp
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues:
- [High] This problem wasn't introduced by this patch, but the patch fails to fully resolve the issue it claims to fix: Metadata mismatch for delayed/throttled CAN frames. `op->rx_stamp` and `op->rx_ifindex` are overwritten by subsequent frames, causing delayed frames to be delivered with incorrect timestamps and originator ifindexes.
--
--- Patch [10]: [PATCH v8 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() ---
commit 1903094034673eeaf05aa58b49f4d0ff45d06795
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
This commit addresses data races and torn stores on rx_stamp and rx_ifindex
by moving their assignment inside the bcm_rx_update_lock section in
bcm_rx_handler(). It ensures CAN content and metadata are bundled correctly.
Link: https://lore.kernel.org/linux-can/20260707145135.5BC831F00A3A@smtp.kernel.org/
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index 66dd8789843b5..1986d33a7d279 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
[ ... ]
> @@ -805,6 +800,14 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
>
> 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;
[Severity: High]
This isn't a bug introduced by this patch, but does this fully resolve the
metadata mismatch for delayed or throttled CAN frames?
Since op->rx_stamp and op->rx_ifindex are unconditionally updated here, will
they overwrite the metadata corresponding to pending throttled frames?
If an application configures a BCM socket with a throttle timer (kt_ival2 > 0)
and a frame is marked for delayed delivery, a subsequent frame arriving before
the timer expires will overwrite this global metadata.
When the timer expires and the delayed frame is eventually flushed to user
space via bcm_send_to_user(), it will be sent with the clobbered
op->rx_ifindex rather than the interface it originally arrived on. Could this
lead to the user application receiving an incorrect source interface and
potentially responding on the wrong CAN bus?
> +
> if (op->flags & RX_FILTER_ID) {
> /* the easiest case */
> bcm_rx_update_and_send(op, op->last_frames, rxframe,
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260708-bcm_fixes-v8-0-8c2f5f3bc212@hartkopp.net?part=10
^ permalink raw reply [flat|nested] 19+ messages in thread* Re: [PATCH v8 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
2026-07-08 17:47 ` sashiko-bot
@ 2026-07-08 18:38 ` Oliver Hartkopp
0 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp @ 2026-07-08 18:38 UTC (permalink / raw)
To: sashiko-reviews
Cc: linux-can, Oleksij Rempel, Vincent Mailhol, Marc Kleine-Budde
On 08.07.26 19:47, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
>
> Pre-existing issues:
> - [High] This problem wasn't introduced by this patch, but the patch fails to fully resolve the issue it claims to fix: Metadata mismatch for delayed/throttled CAN frames. `op->rx_stamp` and `op->rx_ifindex` are overwritten by subsequent frames, causing delayed frames to be delivered with incorrect timestamps and originator ifindexes.
> --
>
> --- Patch [10]: [PATCH v8 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() ---
> commit 1903094034673eeaf05aa58b49f4d0ff45d06795
> Author: Oliver Hartkopp <socketcan@hartkopp.net>
>
> can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
>
> This commit addresses data races and torn stores on rx_stamp and rx_ifindex
> by moving their assignment inside the bcm_rx_update_lock section in
> bcm_rx_handler(). It ensures CAN content and metadata are bundled correctly.
>
> Link: https://lore.kernel.org/linux-can/20260707145135.5BC831F00A3A@smtp.kernel.org/
>
>> diff --git a/net/can/bcm.c b/net/can/bcm.c
>> index 66dd8789843b5..1986d33a7d279 100644
>> --- a/net/can/bcm.c
>> +++ b/net/can/bcm.c
>
> [ ... ]
>
>> @@ -805,6 +800,14 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
>>
>> 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;
>
> [Severity: High]
> This isn't a bug introduced by this patch, but does this fully resolve the
> metadata mismatch for delayed or throttled CAN frames?
>
> Since op->rx_stamp and op->rx_ifindex are unconditionally updated here, will
> they overwrite the metadata corresponding to pending throttled frames?
>
> If an application configures a BCM socket with a throttle timer (kt_ival2 > 0)
> and a frame is marked for delayed delivery, a subsequent frame arriving before
> the timer expires will overwrite this global metadata.
>
> When the timer expires and the delayed frame is eventually flushed to user
> space via bcm_send_to_user(), it will be sent with the clobbered
> op->rx_ifindex rather than the interface it originally arrived on. Could this
> lead to the user application receiving an incorrect source interface and
> potentially responding on the wrong CAN bus?
>
Good finding!
Using the ANY CAN device for bcm rx_ops is a corner case anyway that has
been allowed for completeness. So when a specific CAN ID is configured
with ANY CAN device as a rx_op the meta data might become unreliable
when this same CAN ID shows up on different interfaces in the throttle mode.
There is no known use-case for the throttle mode together with ANYDEV as
the throttle mode is intended and designed to throttle a single(!) data
source. Not multiple. So we can change the 20 y/o API and throw an error
when someone configures a throttle mode together with ANYDEV. Or we can
leave it as-is to maintain some auto-detect functionality that e.g. the
interface is not needed to be provided.
>> +
>> if (op->flags & RX_FILTER_ID) {
>> /* the easiest case */
>> bcm_rx_update_and_send(op, op->last_frames, rxframe,
>
^ permalink raw reply [flat|nested] 19+ messages in thread
* Re: [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/
2026-07-08 17:26 [PATCH v8 00/10] can: bcm: collected fixes - final3 :-/ Oliver Hartkopp via B4 Relay
` (9 preceding siblings ...)
2026-07-08 17:27 ` [PATCH v8 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() Oliver Hartkopp via B4 Relay
@ 2026-07-08 21:23 ` Marc Kleine-Budde
10 siblings, 0 replies; 19+ messages in thread
From: Marc Kleine-Budde @ 2026-07-08 21:23 UTC (permalink / raw)
To: Oliver Hartkopp via B4 Relay
Cc: linux-can, Oliver Hartkopp, Lee Jones, Feng Xue, Ginger,
syzbot+75e5e4ae00c3b4bb544e, sashiko-reviews, sashiko-bot
[-- Attachment #1: Type: text/plain, Size: 1467 bytes --]
On 08.07.2026 19:26:57, Oliver Hartkopp via B4 Relay wrote:
> Hi Marc,
>
> as there were different patches flying arround to fix CAN_BCM issues and
> AI assisted stuff pop's up again and again, I've created this collection
> to be applied.
>
> The patch series fixes ALL issues reported by ALL kind of AI bots involved
> and the fixes were assisted by claude code and later rephrased and shortened
> by myself.
>
> Inserted a new patch 9 that addresses a late sashiko-bot report fixing some
> stale rx/tx ops behaviour after device removal.
>
> Btw. I added a bug when reworking the patch that sashiko-bot found.
>
> So the potential new AI reports on this patch set report problems that are
> solved later in the series. This can not be resolved.
What about the issues that, according to the Sashiko bot, are supposed
to occur in Patch 4:
New issues:
- [Medium] `bcm_update_stats()` can be executed concurrently from
different lock domains, contradicting the commit's claim of preventing
races during counter reset.
- [Medium] TX operations incorrectly inherit the RX-specific statistics
cap, causing premature zeroing of the TX frame counter.
regards,
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung Nürnberg | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 |
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^ permalink raw reply [flat|nested] 19+ messages in thread