From: Oliver Hartkopp socketcan@hartkopp.net

When receiving a CAN frame the current code logic does not consider concurrently receiving processes which do not show up in real world usage.

Ziyang Xuan writes:

The following syz problem is one of the scenarios. so->rx.len is changed by isotp_rcv_ff() during isotp_rcv_cf(), so->rx.len equals 0 before alloc_skb() and equals 4096 after alloc_skb(). That will trigger skb_over_panic() in skb_put().

======================================================= CPU: 1 PID: 19 Comm: ksoftirqd/1 Not tainted 5.16.0-rc8-syzkaller #0 RIP: 0010:skb_panic+0x16c/0x16e net/core/skbuff.c:113 Call Trace: <TASK> skb_over_panic net/core/skbuff.c:118 [inline] skb_put.cold+0x24/0x24 net/core/skbuff.c:1990 isotp_rcv_cf net/can/isotp.c:570 [inline] isotp_rcv+0xa38/0x1e30 net/can/isotp.c:668 deliver net/can/af_can.c:574 [inline] can_rcv_filter+0x445/0x8d0 net/can/af_can.c:635 can_receive+0x31d/0x580 net/can/af_can.c:665 can_rcv+0x120/0x1c0 net/can/af_can.c:696 __netif_receive_skb_one_core+0x114/0x180 net/core/dev.c:5465 __netif_receive_skb+0x24/0x1b0 net/core/dev.c:5579

Therefore we make sure the state changes and data structures stay consistent at CAN frame reception time by adding a spin_lock in isotp_rcv(). This fixes the issue reported by syzkaller but does not affect real world operation.

Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol") Link: https://lore.kernel.org/linux-can/d7e69278-d741-c706-65e1-e87623d9a8e8@huawe... Link: https://lore.kernel.org/all/20220208200026.13783-1-socketcan@hartkopp.net Cc: stable@vger.kernel.org Reported-by: syzbot+4c63f36709a642f801c5@syzkaller.appspotmail.com Reported-by: Ziyang Xuan william.xuanziyang@huawei.com Signed-off-by: Oliver Hartkopp socketcan@hartkopp.net Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- net/can/isotp.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c index 02cbcb2ecf0d..9149e8d8aefc 100644 --- a/net/can/isotp.c +++ b/net/can/isotp.c @@ -56,6 +56,7 @@ #include <linux/module.h> #include <linux/init.h> #include <linux/interrupt.h> +#include <linux/spinlock.h> #include <linux/hrtimer.h> #include <linux/wait.h> #include <linux/uio.h> @@ -145,6 +146,7 @@ struct isotp_sock { struct tpcon rx, tx; struct list_head notifier; wait_queue_head_t wait; + spinlock_t rx_lock; /* protect single thread state machine */ };

static LIST_HEAD(isotp_notifier_list); @@ -615,11 +617,17 @@ static void isotp_rcv(struct sk_buff *skb, void *data)

n_pci_type = cf->data[ae] & 0xF0;

+ /* Make sure the state changes and data structures stay consistent at + * CAN frame reception time. This locking is not needed in real world + * use cases but the inconsistency can be triggered with syzkaller. + */ + spin_lock(&so->rx_lock); + if (so->opt.flags & CAN_ISOTP_HALF_DUPLEX) { /* check rx/tx path half duplex expectations */ if ((so->tx.state != ISOTP_IDLE && n_pci_type != N_PCI_FC) || (so->rx.state != ISOTP_IDLE && n_pci_type == N_PCI_FC)) - return; + goto out_unlock; }

switch (n_pci_type) { @@ -668,6 +676,9 @@ static void isotp_rcv(struct sk_buff *skb, void *data) isotp_rcv_cf(sk, cf, ae, skb); break; } + +out_unlock: + spin_unlock(&so->rx_lock); }

static void isotp_fill_dataframe(struct canfd_frame *cf, struct isotp_sock *so, @@ -1444,6 +1455,7 @@ static int isotp_init(struct sock *sk) so->txtimer.function = isotp_tx_timer_handler;

init_waitqueue_head(&so->wait); + spin_lock_init(&so->rx_lock);

spin_lock(&isotp_notifier_lock); list_add_tail(&so->notifier, &isotp_notifier_list);

base-commit: 7db788ad627aabff2b74d4f1a3b68516d0fee0d7