[PATCH 6.18 191/309] can: isotp: fix tx.buf use-after-free in isotp_sendmsg()

Greg Kroah-Hartman
2026-03-31T17:04:53Z

From: Oliver Hartkopp <socketcan@hartkopp.net>

commit 424e95d62110cdbc8fd12b40918f37e408e35a92 upstream.

isotp_sendmsg() uses only cmpxchg() on so->tx.state to serialize access
to so->tx.buf. isotp_release() waits for ISOTP_IDLE via
wait_event_interruptible() and then calls kfree(so->tx.buf).

If a signal interrupts the wait_event_interruptible() inside close()
while tx.state is ISOTP_SENDING, the loop exits early and release
proceeds to force ISOTP_SHUTDOWN and continues to kfree(so->tx.buf)
while sendmsg may still be reading so->tx.buf for the final CAN frame
in isotp_fill_dataframe().

The so->tx.buf can be allocated once when the standard tx.buf length needs
to be extended. Move the kfree() of this potentially extended tx.buf to
sk_destruct time when either isotp_sendmsg() and isotp_release() are done.

Fixes: 96d1c81e6a04 ("can: isotp: add module parameter for maximum pdu size")
Cc: stable@vger.kernel.org
Reported-by: Ali Norouzi <ali.norouzi@keysight.com>
Co-developed-by: Ali Norouzi <ali.norouzi@keysight.com>
Signed-off-by: Ali Norouzi <ali.norouzi@keysight.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260319-fix-can-gw-and-can-isotp-v2-2-c45d52c6d2d8@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/can/isotp.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)

--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -1230,12 +1230,6 @@ static int isotp_release(struct socket *
so->ifindex = 0;
so->bound = 0;

- if (so->rx.buf != so->rx.sbuf)
- kfree(so->rx.buf);
-
- if (so->tx.buf != so->tx.sbuf)
- kfree(so->tx.buf);
-
sock_orphan(sk);
sock->sk = NULL;

@@ -1604,6 +1598,21 @@ static int isotp_notifier(struct notifie
return NOTIFY_DONE;
}

+static void isotp_sock_destruct(struct sock *sk)
+{
+ struct isotp_sock *so = isotp_sk(sk);
+
+ /* do the standard CAN sock destruct work */
+ can_sock_destruct(sk);
+
+ /* free potential extended PDU buffers */
+ if (so->rx.buf != so->rx.sbuf)
+ kfree(so->rx.buf);
+
+ if (so->tx.buf != so->tx.sbuf)
+ kfree(so->tx.buf);
+}
+
static int isotp_init(struct sock *sk)
{
struct isotp_sock *so = isotp_sk(sk);
@@ -1648,6 +1657,9 @@ static int isotp_init(struct sock *sk)
list_add_tail(&so->notifier, &isotp_notifier_list);
spin_unlock(&isotp_notifier_lock);

+ /* re-assign default can_sock_destruct() reference */
+ sk->sk_destruct = isotp_sock_destruct;
+
return 0;
}