* [PATCH v10 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:38 ` sashiko-bot
2026-07-09 10:24 ` [PATCH v10 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 @ 2026-07-09 10:24 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 v10 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
2026-07-09 10:24 ` [PATCH v10 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:38 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-09 10:38 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: linux-can, Oliver Hartkopp, Oleksij Rempel, Vincent Mailhol,
Marc Kleine-Budde
Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
Pre-existing issues:
- [High] Inconsistent use of RCU list primitives can lead to data races and crashes when reading `/proc/net/can-bcm/*`.
- [High] Data race on `op->frames` during runtime updates in `bcm_tx_setup()` and `bcm_rx_setup()`.
--
--- Patch [1]: [PATCH v10 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF ---
commit 07fedad11f0f52be9c8ac130e930be315886f42d
Author: Lee Jones <lee@kernel.org>
can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
Commit f1b4e32aca08 replaced synchronize_rcu() with call_rcu() but
omitted flag checks for thrtimer, creating a TOCTOU race and UAF.
This resolves the race by deferring timer cancellation and memory free
to a dedicated unbound workqueue, which avoids sleeping in RCU callbacks.
> 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 I noticed it while reviewing the op setup
changes. Does the list insertion in bcm_tx_setup() and bcm_rx_setup() need
to use list_add_rcu() instead of list_add()?
It looks like bcm_tx_setup() adds to the list like this:
net/can/bcm.c:bcm_tx_setup() {
...
list_add(&op->list, &bo->tx_ops);
...
}
Since readers like bcm_proc_show() iterate the tx_ops list inside an RCU
read-side critical section, could the lack of memory barriers in list_add()
allow a lockless reader to observe a partially initialized list node?
Also, bcm_proc_show() appears to use the non-RCU list_for_each_entry()
iterator.
[Severity: High]
This isn't a bug introduced by this patch, but there might be a data race on
op->frames during runtime updates.
In bcm_tx_setup() and bcm_rx_setup(), it appears the memory content of
op->frames can be updated directly from userspace messages:
net/can/bcm.c:bcm_tx_setup() {
...
err = memcpy_from_msg((u8 *)cf, msg, op->cfsiz);
...
}
Does this allow concurrent readers to access partially updated memory?
For example, bcm_can_tx() calculates the frame pointer under op->bcm_tx_lock
but then accesses the memory content via skb_put_data() outside the lock.
Could this result in torn CAN frames being transmitted, or incorrect rx
filtering if a concurrent bcm_rx_handler() reads op->frames while it is
being modified?
[ ... ]
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v10-0-57fff38e34ce@hartkopp.net?part=1
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v10 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
2026-07-09 10:24 ` [PATCH v10 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:44 ` sashiko-bot
2026-07-09 11:58 ` Marc Kleine-Budde
2026-07-09 10:24 ` [PATCH v10 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
` (8 subsequent siblings)
10 siblings, 2 replies; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 10:24 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 v10 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
2026-07-09 10:24 ` [PATCH v10 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:44 ` sashiko-bot
2026-07-09 11:58 ` Marc Kleine-Budde
1 sibling, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-09 10:44 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Oliver Hartkopp, Vincent Mailhol, Oleksij Rempel, linux-can,
Marc Kleine-Budde
Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
Pre-existing issues:
- [High] Missing RCU protection and memory barriers for `tx_ops` and `rx_ops` list modifications and traversals.
- [High] Lockless modification of CAN frames and filters from process context while they are concurrently read by softirq handlers.
--
--- Patch [2]: [PATCH v10 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure ---
commit 14fe77d5df361ef7f02ad605d5649032b1cb3565
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
This commit fixes an unordered read/write race in bcm_sendmsg() between
bo->bound and bo->ifindex by moving the re-check into the locked section.
It also ensures bcm_rx_setup() returns an error if the target device
disappears concurrently instead of silently succeeding.
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
[ ... ]
> @@ -1436,20 +1463,21 @@ static int bcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
> 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:
[Severity: High]
This is a pre-existing issue, but does this lack of RCU protection and memory
barriers allow a lockless reader to observe uninitialized fields?
Looking at bcm_proc_show(), it traverses bo->tx_ops locklessly under
rcu_read_lock():
list_for_each_entry(op, &bo->tx_ops, list) {
Concurrently, bcm_tx_setup() can add a new operation to this list:
list_add(&op->list, &bo->tx_ops);
Because list_add() lacks the smp_store_release() memory barrier provided
by list_add_rcu(), and the traversal uses the non-RCU
list_for_each_entry() macro, can concurrent readers see torn pointers or
uninitialized bcm_op fields, potentially causing a kernel crash when
reading uninitialized memory?
[Severity: High]
This is a pre-existing issue, but does this lockless modification of CAN
frames allow softirq readers to see partially updated data?
In bcm_tx_setup() and bcm_rx_setup(), op->frames are modified directly
from process context:
bcm_tx_setup():
err = memcpy_from_msg((u8 *)cf, msg, op->cfsiz);
bcm_rx_setup():
err = memcpy_from_msg(op->frames, msg, msg_head->nframes * op->cfsiz);
Concurrently, softirq handlers read these frames locklessly. For example,
bcm_can_tx() reads frames from timer context to transmit:
skb_put_data(skb, cf, op->cfsiz);
And bcm_rx_cmp_to_index() reads filter mask frames from RX softirq context:
if ((get_u64(cf, i) & get_u64(rxdata, i)) != ...
Can this data race result in transmitting torn or functionally corrupted
CAN frames to the network bus, or incorrect evaluation of incoming packets
against partially updated filter masks?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v10-0-57fff38e34ce@hartkopp.net?part=2
^ permalink raw reply [flat|nested] 19+ messages in thread* Re: [PATCH v10 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
2026-07-09 10:24 ` [PATCH v10 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
2026-07-09 10:44 ` sashiko-bot
@ 2026-07-09 11:58 ` Marc Kleine-Budde
2026-07-09 12:58 ` Oliver Hartkopp
1 sibling, 1 reply; 19+ messages in thread
From: Marc Kleine-Budde @ 2026-07-09 11:58 UTC (permalink / raw)
To: Oliver Hartkopp via B4 Relay; +Cc: linux-can, Oliver Hartkopp, Ginger
[-- Attachment #1: Type: text/plain, Size: 1982 bytes --]
On 09.07.2026 12:24:16, Oliver Hartkopp via B4 Relay wrote:
> 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>
Can you give me the Fixes: tag?
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 |
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]
^ permalink raw reply [flat|nested] 19+ messages in thread
* Re: [PATCH v10 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure
2026-07-09 11:58 ` Marc Kleine-Budde
@ 2026-07-09 12:58 ` Oliver Hartkopp
0 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp @ 2026-07-09 12:58 UTC (permalink / raw)
To: Marc Kleine-Budde, Oliver Hartkopp via B4 Relay; +Cc: linux-can, Ginger
On 09.07.26 13:58, Marc Kleine-Budde wrote:
> On 09.07.2026 12:24:16, Oliver Hartkopp via B4 Relay wrote:
>> 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>
>
> Can you give me the Fixes: tag?
Yes. I'll send a v11 with a fixes tag and another patch addressing these
issues from patch 10:
- [High] Spurious RX_TIMEOUT notification and state corruption due to a
race between concurrent bcm_rx_handler execution and op->timer expiration.
- [High] Throttled multiplex frames share a single metadata store,
leading to incorrect interface index (rx_ifindex) and timestamps being
sent to userspace.
The binding of a rx_op to ANYDEV (ifindex = 0) leads to multiple
problems for the timeout monitoring and throttling of CAN frames as they
are only intended to work with a single source.
I'm thinking of some autodetect interface that grabs the first interface
from a configured CAN ID and provides the timer functionality for this
stream until it is handled. Anything else makes so semantic sense.
Stay tuned ;-)
Many thanks,
Oliver
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v10 03/10] can: bcm: add locking when updating filter and timer values
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
2026-07-09 10:24 ` [PATCH v10 01/10] can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Oliver Hartkopp via B4 Relay
2026-07-09 10:24 ` [PATCH v10 02/10] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:52 ` sashiko-bot
2026-07-09 10:24 ` [PATCH v10 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 @ 2026-07-09 10:24 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 v10 03/10] can: bcm: add locking when updating filter and timer values
2026-07-09 10:24 ` [PATCH v10 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:52 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-09 10:52 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: linux-can, Oleksij Rempel, Oliver Hartkopp, Vincent Mailhol,
Marc Kleine-Budde
Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
Pre-existing issues:
- [High] Lockless `memcpy_from_msg()` in `bcm_tx_setup()` defeats the `bcm_can_tx()` lock-protected snapshot, leading to torn CAN frames and potentially transmitting unvalidated malicious lengths.
- [High] Missing frame payload length validation for `RX_RTR_FRAME` operations in `bcm_rx_setup()`, leading to downstream out-of-bounds reads during automated RTR replies.
- [Medium] Metadata `rx_stamp`, `rx_ifindex`, and `frames_abs` are updated outside the newly introduced `bcm_rx_update_lock` in `bcm_rx_handler()`, leading to torn metadata for concurrent packet receptions.
- [Medium] Timer fields and counters (`kt_ival1`, `kt_ival2`, `count`) are read without locking in `bcm_tx_timeout_handler()`, leading to potential logic flaws and torn reads.
--
--- Patch [3]: [PATCH v10 03/10] can: bcm: add locking when updating filter and timer values ---
commit 3f8b487ac0338cf76d904d74f58ed7c66c12d1fb
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: add locking when updating filter and timer values
This patch adds a new per-op bcm_rx_update_lock to protect timer and filter
updates in bcm_rx_setup() against concurrent access from RX handlers. It
also stages memcpy_from_msg() into a temporary buffer to avoid sleeping
while holding a spinlock, and closes a race condition where a stale reply
with CAN_RTR_FLAG could be transmitted.
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
[ ... ]
> @@ -293,22 +294,26 @@ 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);
> + }
[Severity: High]
This is a pre-existing issue, but does bcm_tx_setup() update op->frames
locklessly?
If a concurrent bcm_can_tx() is driven by the TX timer while the user
updates an existing TX operation, bcm_tx_setup() copies data into the active
op->frames without taking a lock:
net/can/bcm.c:bcm_tx_setup() {
...
cf = op->frames + op->cfsiz * i;
err = memcpy_from_msg((u8 *)cf, msg, op->cfsiz);
...
}
Because memcpy_from_msg() can sleep, it happens without the spinlock,
which could allow an attacker to concurrently write a malicious payload
length.
Could this lead to a torn read of the CAN frame in bcm_can_tx() and a
transmission of an unvalidated length, resulting in an out-of-bounds read?
[ ... ]
> @@ -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);
> if (!op->count && (op->flags & TX_COUNTEVT)) {
[Severity: Medium]
This is a pre-existing issue, but are the timer and count fields read here
subject to concurrent updates?
bcm_tx_timeout_handler() evaluates op->kt_ival1, op->kt_ival2, and op->count
without holding the bcm_tx_lock.
Meanwhile, bcm_tx_setup() can update these timer values locklessly in process
context. Additionally, op->count can be decremented by another thread executing
bcm_can_tx() concurrently.
Could this lead to torn reads of 64-bit ktime_t values on 32-bit platforms,
causing unexpected timer expiries or incorrect notifications?
[ ... ]
> @@ -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);
> + rtr_frame = op->flags & RX_RTR_FRAME;
> + if (rtr_frame)
> + memcpy(&rtrframe, op->frames, op->cfsiz);
> + spin_unlock_bh(&op->bcm_rx_update_lock);
[Severity: Medium]
This is a pre-existing issue, but are some metadata updates still left
unprotected by the new lock?
Just above this section, metadata fields are modified outside the lock:
net/can/bcm.c:bcm_rx_handler() {
...
op->rx_stamp = skb->tstamp;
op->rx_ifindex = skb->dev->ifindex;
...
op->frames_abs++;
...
}
If an operation is bound to all interfaces (ifindex = 0) and receives frames
concurrently on multiple CPUs, could these updates overwrite op->rx_ifindex
before bcm_send_to_user() dispatches it inside the critical section?
Would this result in userspace receiving incorrectly bundled metadata,
such as a packet from can0 tagged with the timestamp and ifindex of can1?
[ ... ]
> @@ -1130,6 +1165,24 @@ static int bcm_tx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
> 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;
> + }
> +}
[Severity: High]
This isn't a bug introduced by this patch, but does the handling for
RX_RTR_FRAME lack payload length validation?
If a user configures an RX_SETUP operation with RX_RTR_FRAME and provides
a CAN frame with a malicious length (for example, len = 255),
bcm_rx_setup_rtr_check() normalizes the RTR flag but doesn't validate
the payload length bounds.
When an incoming RTR frame triggers the automated reply, bcm_rx_handler()
passes this unvalidated frame to bcm_can_tx():
net/can/bcm.c:bcm_rx_handler() {
...
if (rtr_frame) {
bcm_can_tx(op, &rtrframe);
return;
}
...
}
Could the CAN driver trust cf->len and read beyond the allocated buffer,
leading to an out-of-bounds slab read that leaks kernel memory onto the bus?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v10-0-57fff38e34ce@hartkopp.net?part=3
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v10 04/10] can: bcm: fix CAN frame rx/tx statistics
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
` (2 preceding siblings ...)
2026-07-09 10:24 ` [PATCH v10 03/10] can: bcm: add locking when updating filter and timer values Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:24 ` [PATCH v10 05/10] can: bcm: add missing rcu list annotations and operations Oliver Hartkopp via B4 Relay
` (6 subsequent siblings)
10 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 10:24 UTC (permalink / raw)
To: linux-can; +Cc: Oliver Hartkopp, Marc Kleine-Budde
From: Oliver Hartkopp <socketcan@hartkopp.net>
KCSAN detected a data race within the bcm_rx_handler() when two CAN frames
have been simultaneously received and processed in a single rx op by two
different CPUs.
Use atomic operations with (signed) long data types to access the
statistics in the hot path to fix the KCSAN complaint.
Additionally simplify the update and check of statistics overflow by
using the atomic operations in separate bcm_update_[rx|tx]_stats()
functions. The rx variant runs under bcm_rx_update_lock to prevent
races when resetting the two rx counters; the tx variant runs under
bcm_tx_lock and only needs to guard its own counter's overflow.
As the rx path resets its values already at LONG_MAX / 100, there is
no conflict between the two locking domains (bcm_rx_update_lock vs.
bcm_tx_lock) even for ops that use both paths.
The rx statistics update and the frames_filtered update in
bcm_rx_changed() were previously performed in two separate
bcm_rx_update_lock sections. For an rx op subscribed on all interfaces
(ifindex == 0), bcm_rx_handler() can run concurrently on different
CPUs, so a counter reset by one CPU between these two sections could
leave frames_filtered larger than frames_abs on another CPU, producing
a bogus (even negative) reduction percentage in procfs. Update the
statistics in the same critical section as bcm_rx_changed() to close
this gap, which also removes the now unneeded extra lock/unlock pair
around the traffic_flags calculation.
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/bcm.c | 69 +++++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 46 insertions(+), 23 deletions(-)
diff --git a/net/can/bcm.c b/net/can/bcm.c
index af4bb4182bc2..38c3f690c1cd 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -110,11 +110,11 @@ struct bcm_op {
struct rcu_head rcu;
struct work_struct work;
int ifindex;
canid_t can_id;
u32 flags;
- unsigned long frames_abs, frames_filtered;
+ atomic_long_t frames_abs, frames_filtered;
struct bcm_timeval ival1, ival2;
struct hrtimer timer, thrtimer;
ktime_t rx_stamp, kt_ival1, kt_ival2, kt_lastmsg;
int rx_ifindex;
int cfsiz;
@@ -227,14 +227,17 @@ static int bcm_proc_show(struct seq_file *m, void *v)
rcu_read_lock();
list_for_each_entry_rcu(op, &bo->rx_ops, list) {
- unsigned long reduction;
+ long reduction, frames_filtered, frames_abs;
+
+ frames_filtered = atomic_long_read(&op->frames_filtered);
+ frames_abs = atomic_long_read(&op->frames_abs);
/* print only active entries & prevent division by zero */
- if (!op->frames_abs)
+ if (!frames_abs)
continue;
seq_printf(m, "rx_op: %03X %-5s ", op->can_id,
bcm_proc_getifname(net, ifname, op->ifindex));
@@ -252,13 +255,13 @@ static int bcm_proc_show(struct seq_file *m, void *v)
if (op->kt_ival2)
seq_printf(m, "thr=%lld ",
(long long)ktime_to_us(op->kt_ival2));
seq_printf(m, "# recv %ld (%ld) => reduction: ",
- op->frames_filtered, op->frames_abs);
+ frames_filtered, frames_abs);
- reduction = 100 - (op->frames_filtered * 100) / op->frames_abs;
+ reduction = 100 - (frames_filtered * 100) / frames_abs;
seq_printf(m, "%s%ld%%\n",
(reduction == 100) ? "near " : "", reduction);
}
@@ -278,20 +281,39 @@ static int bcm_proc_show(struct seq_file *m, void *v)
if (op->kt_ival2)
seq_printf(m, "t2=%lld ",
(long long)ktime_to_us(op->kt_ival2));
- seq_printf(m, "# sent %ld\n", op->frames_abs);
+ seq_printf(m, "# sent %ld\n",
+ atomic_long_read(&op->frames_abs));
}
seq_putc(m, '\n');
rcu_read_unlock();
return 0;
}
#endif /* CONFIG_PROC_FS */
+static void bcm_update_rx_stats(struct bcm_op *op)
+{
+ /* prevent overflow of the reduction% calculation in bcm_proc_show() */
+ if (atomic_long_inc_return(&op->frames_abs) > LONG_MAX / 100) {
+ atomic_long_set(&op->frames_filtered, 0);
+ atomic_long_set(&op->frames_abs, 0);
+ }
+}
+
+static void bcm_update_tx_stats(struct bcm_op *op)
+{
+ /* tx_op has no reduction% calculation - use the full range and
+ * just keep the displayed counter non-negative on overflow
+ */
+ if (atomic_long_inc_return(&op->frames_abs) == LONG_MAX)
+ atomic_long_set(&op->frames_abs, 0);
+}
+
/*
* bcm_can_tx - send the (next) CAN frame to the appropriate CAN interface
* of the given bcm tx op
*/
static void bcm_can_tx(struct bcm_op *op, struct canfd_frame *cf)
@@ -342,11 +364,11 @@ static void bcm_can_tx(struct bcm_op *op, struct canfd_frame *cf)
/* update currframe and count under lock protection */
spin_lock_bh(&op->bcm_tx_lock);
if (!err)
- op->frames_abs++;
+ bcm_update_tx_stats(op);
op->currframe++;
/* reached last frame? */
if (op->currframe >= op->nframes)
@@ -495,16 +517,13 @@ static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
*/
static void bcm_rx_changed(struct bcm_op *op, struct canfd_frame *data)
{
struct bcm_msg_head head;
- /* update statistics */
- op->frames_filtered++;
-
- /* prevent statistics overflow */
- if (op->frames_filtered > ULONG_MAX/100)
- op->frames_filtered = op->frames_abs = 0;
+ /* update statistics (frames_filtered <= frames_abs) */
+ if (atomic_long_read(&op->frames_abs))
+ atomic_long_inc(&op->frames_filtered);
/* this element is not throttled anymore */
data->flags &= ~RX_THR;
memset(&head, 0, sizeof(head));
@@ -746,38 +765,42 @@ 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().
- */
+ /* 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)
+ if (rtr_frame) {
+ bcm_update_rx_stats(op);
+ /* snapshot RTR content under lock */
memcpy(&rtrframe, op->frames, op->cfsiz);
- spin_unlock_bh(&op->bcm_rx_update_lock);
+ 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);
return;
}
+ /* update statistics in the same critical section as bcm_rx_changed()
+ * below: frames_filtered must never be checked/incremented against a
+ * frames_abs snapshot from a concurrent bcm_rx_handler() call on
+ * another CPU for the same (wildcard) op, or frames_filtered can end
+ * up larger than frames_abs.
+ */
+ bcm_update_rx_stats(op);
+
/* compute flags to distinguish between own/local/remote CAN traffic */
traffic_flags = 0;
if (skb->sk) {
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;
--
2.53.0
^ permalink raw reply related [flat|nested] 19+ messages in thread* [PATCH v10 05/10] can: bcm: add missing rcu list annotations and operations
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
` (3 preceding siblings ...)
2026-07-09 10:24 ` [PATCH v10 04/10] can: bcm: fix CAN frame rx/tx statistics Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:24 ` [PATCH v10 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates Oliver Hartkopp via B4 Relay
` (5 subsequent siblings)
10 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 10:24 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 38c3f690c1cd..940cd9df1cca 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)
@@ -1007,10 +1007,11 @@ 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)
@@ -1148,12 +1149,11 @@ 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 */
@@ -1171,10 +1171,14 @@ 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);
@@ -1355,13 +1359,10 @@ 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))) */
@@ -1429,14 +1430,16 @@ 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;
}
@@ -1766,12 +1769,14 @@ 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.
@@ -1798,12 +1803,14 @@ 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* [PATCH v10 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
` (4 preceding siblings ...)
2026-07-09 10:24 ` [PATCH v10 05/10] can: bcm: add missing rcu list annotations and operations Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:24 ` [PATCH v10 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 @ 2026-07-09 10:24 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 940cd9df1cca..18601d6fdf76 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -126,11 +126,11 @@ struct bcm_op {
void *last_frames;
struct canfd_frame sframe;
struct canfd_frame last_sframe;
struct sock *sk;
struct net_device *rx_reg_dev;
- spinlock_t bcm_tx_lock; /* protect currframe/count in runtime updates */
+ spinlock_t bcm_tx_lock; /* protect tx data and timer updates */
spinlock_t bcm_rx_update_lock; /* protect filter/timer data updates */
};
struct bcm_sock {
struct sock sk;
@@ -462,16 +462,22 @@ static void bcm_send_to_user(struct bcm_op *op, struct bcm_msg_head *head,
static bool bcm_tx_set_expiry(struct bcm_op *op, struct hrtimer *hrt)
{
ktime_t ival;
+ spin_lock_bh(&op->bcm_tx_lock);
+
if (op->kt_ival1 && op->count)
ival = op->kt_ival1;
- else if (op->kt_ival2)
+ else if (op->kt_ival2) {
ival = op->kt_ival2;
- else
+ } else {
+ spin_unlock_bh(&op->bcm_tx_lock);
return false;
+ }
+
+ spin_unlock_bh(&op->bcm_tx_lock);
hrtimer_set_expires(hrt, ktime_add(ktime_get(), ival));
return true;
}
@@ -484,12 +490,21 @@ static void bcm_tx_start_timer(struct bcm_op *op)
/* bcm_tx_timeout_handler - performs cyclic CAN frame transmissions */
static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
{
struct bcm_op *op = container_of(hrtimer, struct bcm_op, timer);
struct bcm_msg_head msg_head;
+ bool tx_ival1, tx_ival2;
- if (op->kt_ival1 && (op->count > 0)) {
+ /* snapshot kt_ival1/kt_ival2/count under lock to avoid torn
+ * ktime_t reads racing with concurrent bcm_tx_setup() updates
+ */
+ spin_lock_bh(&op->bcm_tx_lock);
+ tx_ival1 = op->kt_ival1 && (op->count > 0);
+ tx_ival2 = !!op->kt_ival2;
+ spin_unlock_bh(&op->bcm_tx_lock);
+
+ if (tx_ival1) {
bcm_can_tx(op, NULL);
if (!op->count && (op->flags & TX_COUNTEVT)) {
/* create notification to user */
memset(&msg_head, 0, sizeof(msg_head));
@@ -502,11 +517,11 @@ static enum hrtimer_restart bcm_tx_timeout_handler(struct hrtimer *hrtimer)
msg_head.nframes = 0;
bcm_send_to_user(op, &msg_head, NULL, 0);
}
- } else if (op->kt_ival2) {
+ } else if (tx_ival2) {
bcm_can_tx(op, NULL);
}
return bcm_tx_set_expiry(op, &op->timer) ?
HRTIMER_RESTART : HRTIMER_NORESTART;
@@ -1026,64 +1041,80 @@ 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);
@@ -1155,14 +1186,16 @@ 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 v10 07/10] can: bcm: validate frame length in bcm_rx_setup() for RTR replies
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
` (5 preceding siblings ...)
2026-07-09 10:24 ` [PATCH v10 06/10] can: bcm: extend bcm_tx_lock usage for data and timer updates Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:24 ` [PATCH v10 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 @ 2026-07-09 10:24 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 18601d6fdf76..3cc3deb98a98 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1223,26 +1223,41 @@ 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)
*/
@@ -1301,11 +1316,15 @@ 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;
@@ -1366,20 +1385,16 @@ 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);
@@ -1472,10 +1487,18 @@ 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 v10 08/10] can: bcm: add missing device refcount for CAN filter removal
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
` (6 preceding siblings ...)
2026-07-09 10:24 ` [PATCH v10 07/10] can: bcm: validate frame length in bcm_rx_setup() for RTR replies Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:51 ` sashiko-bot
2026-07-09 10:24 ` [PATCH v10 09/10] can: bcm: fix stale rx/tx ops after device removal Oliver Hartkopp via B4 Relay
` (2 subsequent siblings)
10 siblings, 1 reply; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 10:24 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 3cc3deb98a98..5660165cdf0e 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 {
@@ -914,10 +915,11 @@ 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);
}
@@ -944,21 +946,18 @@ 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);
@@ -1463,11 +1462,21 @@ 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
*/
@@ -1840,20 +1849,18 @@ 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* Re: [PATCH v10 08/10] can: bcm: add missing device refcount for CAN filter removal
2026-07-09 10:24 ` [PATCH v10 08/10] can: bcm: add missing device refcount for CAN filter removal Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:51 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-09 10:51 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: Marc Kleine-Budde, Vincent Mailhol, Oleksij Rempel, linux-can,
Oliver Hartkopp
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues:
- [Medium] bcm_rx_setup() silently fails to re-register an existing CAN receive filter after a NETDEV_UNREGISTER event, causing silent packet drops.
--
--- Patch [8]: [PATCH v10 08/10] can: bcm: add missing device refcount for CAN filter removal ---
commit 1e97ac5794b00273de0d8b7a26438344b6bbef67
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: add missing device refcount for CAN filter removal
This commit fixes a concurrent device unregistration issue by introducing a
netdevice_tracker. This ensures the bcm code safely holds a reference to the
CAN interface, preventing stale CAN filters from pointing at freed structures
if the device is unlisted before the filter is removed.
Link: https://sashiko.dev/#/patchset/20260707094716.63578-1-socketcan@hartkopp.net
> diff --git a/net/can/bcm.c b/net/can/bcm.c
> index 3cc3deb98a984..5660165cdf0eb 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
[ ... ]
> @@ -1465,7 +1464,17 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
> bcm_rx_handler, op,
> "bcm", sk);
>
> - op->rx_reg_dev = dev;
> + /* 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
[Severity: Medium]
This isn't a bug introduced by this patch, but does bcm_rx_setup() silently
fail to re-register an existing CAN receive filter after a NETDEV_UNREGISTER
event?
If a device is unregistered, bcm_notifier() unregisters the filter and sets
op->rx_reg_dev = NULL, while keeping the op in the socket's list.
If the device is recreated with the same ifindex and the user sends another
RX_SETUP to reconfigure it, bcm_find_op() finds the existing op and
bcm_rx_setup() unconditionally forces do_rx_register to 0 for updates:
/* Only an update -> do not call can_rx_register() */
do_rx_register = 0;
Because of this, the RX_SETUP update succeeds from the user's perspective, but
can_rx_register() is skipped and the filter is left permanently detached,
causing silent packet drops.
Could we check if op->rx_reg_dev is NULL here to ensure we re-register the
filter when needed?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v10-0-57fff38e34ce@hartkopp.net?part=8
^ permalink raw reply [flat|nested] 19+ messages in thread
* [PATCH v10 09/10] can: bcm: fix stale rx/tx ops after device removal
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
` (7 preceding siblings ...)
2026-07-09 10:24 ` [PATCH v10 08/10] can: bcm: add missing device refcount for CAN filter removal Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:24 ` [PATCH v10 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() Oliver Hartkopp via B4 Relay
2026-07-09 11:49 ` [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Marc Kleine-Budde
10 siblings, 0 replies; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 10:24 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 5660165cdf0e..fbf1cbb7c99f 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1264,10 +1264,11 @@ 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;
@@ -1340,12 +1341,19 @@ 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)
@@ -1408,10 +1416,11 @@ 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 */
@@ -1449,11 +1458,14 @@ 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);
@@ -1481,22 +1493,31 @@ 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:
@@ -1712,15 +1733,23 @@ 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 v10 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
` (8 preceding siblings ...)
2026-07-09 10:24 ` [PATCH v10 09/10] can: bcm: fix stale rx/tx ops after device removal Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:24 ` Oliver Hartkopp via B4 Relay
2026-07-09 10:50 ` sashiko-bot
2026-07-09 11:49 ` [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Marc Kleine-Budde
10 siblings, 1 reply; 19+ messages in thread
From: Oliver Hartkopp via B4 Relay @ 2026-07-09 10:24 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 fbf1cbb7c99f..10a883b50fc6 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -777,15 +777,10 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
}
/* disable timeout */
hrtimer_cancel(&op->timer);
- /* save rx timestamp */
- op->rx_stamp = skb->tstamp;
- /* save originator for recvfrom() */
- op->rx_ifindex = skb->dev->ifindex;
-
/* 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) {
@@ -813,10 +808,18 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
traffic_flags |= RX_LOCAL;
if (skb->sk == op->sk)
traffic_flags |= RX_OWN;
}
+ /* 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 v10 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
2026-07-09 10:24 ` [PATCH v10 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() Oliver Hartkopp via B4 Relay
@ 2026-07-09 10:50 ` sashiko-bot
0 siblings, 0 replies; 19+ messages in thread
From: sashiko-bot @ 2026-07-09 10:50 UTC (permalink / raw)
To: Oliver Hartkopp
Cc: linux-can, Oliver Hartkopp, Vincent Mailhol, Marc Kleine-Budde,
Oleksij Rempel
Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
Pre-existing issues:
- [High] Spurious RX_TIMEOUT notification and state corruption due to a race between concurrent bcm_rx_handler execution and op->timer expiration.
- [High] Throttled multiplex frames share a single metadata store, leading to incorrect interface index (rx_ifindex) and timestamps being sent to userspace.
--
--- Patch [10]: [PATCH v10 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() ---
commit d4e0952720604b6c20cb44a753876e69fcdf61ec
Author: Oliver Hartkopp <socketcan@hartkopp.net>
can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
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.
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 fbf1cbb7c99fe..10a883b50fc63 100644
> --- a/net/can/bcm.c
> +++ b/net/can/bcm.c
> @@ -779,11 +779,6 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
> /* disable timeout */
> hrtimer_cancel(&op->timer);
[Severity: High]
This is a pre-existing issue, but could this lockless cancellation cause
spurious RX_TIMEOUT notifications and state corruption?
If a wildcard receive operation receives two frames concurrently on different
CPUs:
CPU1 and CPU2 execute bcm_rx_handler() and both call hrtimer_cancel() outside
the lock. The timer is not yet running, so both return immediately.
CPU1 acquires op->bcm_rx_update_lock, handles its frame, calls
bcm_rx_starttimer() to arm the timer, and releases the lock.
CPU2 acquires op->bcm_rx_update_lock.
The timer expires and bcm_rx_timeout_handler() starts on CPU3, blocking on
the lock.
CPU2 finishes handling its frame, calls bcm_rx_starttimer() to re-arm, and
releases the lock.
CPU3 acquires the lock, clears op->last_frames via memset(), and
unconditionally sends an RX_TIMEOUT, despite CPU2 having just successfully
received a frame?
> - /* save rx timestamp */
> - op->rx_stamp = skb->tstamp;
> - /* save originator for recvfrom() */
> - op->rx_ifindex = skb->dev->ifindex;
> -
> /* op->flags/op->frames may be updated concurrently by bcm_rx_setup() */
> spin_lock_bh(&op->bcm_rx_update_lock);
[ ... ]
> @@ -815,6 +810,14 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data)
> traffic_flags |= RX_OWN;
> }
>
> + /* 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 sharing a single metadata
store for throttled multiplex frames lead to incorrect interface indexes and
timestamps being sent to userspace?
If an RX_SETUP operation is created on all interfaces with multiplex filtering
and throttling:
A frame matching multiplex index 1 arrives on can0. op->rx_ifindex becomes
can0 and the throttle timer starts.
A frame matching multiplex index 2 arrives on can1. op->rx_ifindex is
unconditionally overwritten with can1 here.
When the throttle timer expires, bcm_rx_thr_flush() sends both buffered
frames to userspace:
updated += bcm_rx_do_flush(op, i);
Are both frames then delivered with can_ifindex set to can1 by
bcm_send_to_user(), destroying the origin information of the first frame?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-bcm_fixes-v10-0-57fff38e34ce@hartkopp.net?part=10
^ permalink raw reply [flat|nested] 19+ messages in thread
* Re: [PATCH v10 00/10] can: bcm: collected fixes - final5 :-(
2026-07-09 10:24 [PATCH v10 00/10] can: bcm: collected fixes - final5 :-( Oliver Hartkopp via B4 Relay
` (9 preceding siblings ...)
2026-07-09 10:24 ` [PATCH v10 10/10] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler() Oliver Hartkopp via B4 Relay
@ 2026-07-09 11:49 ` Marc Kleine-Budde
10 siblings, 0 replies; 19+ messages in thread
From: Marc Kleine-Budde @ 2026-07-09 11:49 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
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On 09.07.2026 12:24:14, Oliver Hartkopp via B4 Relay wrote:
> 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.
It seems the sashiko-bot only claims to find per-existing issues. I'll
take them and send upstream.
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