Re: [RFC][PATCH v2] can: isotp: fix CAN frame reception race in isotp_rcv()

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 28.01.2022 08:43:27, Oliver Hartkopp wrote:
> 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.
> 
> Link: https://lore.kernel.org/linux-can/d7e69278-d741-c706-65e1-e87623d9a8e8@huawei.com/T/
> Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
> Reported-by: syzbot+4c63f36709a642f801c5@syzkaller.appspotmail.com
> Reported-by: Ziyang Xuan <william.xuanziyang@huawei.com>
> Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
> ---
>  net/can/isotp.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/net/can/isotp.c b/net/can/isotp.c
> index 02cbcb2ecf0d..b5ba1a9a9e3b 100644
> --- a/net/can/isotp.c
> +++ b/net/can/isotp.c
> @@ -54,10 +54,11 @@
>   */
>  
>  #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>
>  #include <linux/net.h>
>  #include <linux/netdevice.h>
> @@ -143,10 +144,11 @@ struct isotp_sock {
>  	u32 force_tx_stmin;
>  	u32 force_rx_stmin;
>  	struct tpcon rx, tx;
>  	struct list_head notifier;
>  	wait_queue_head_t wait;
> +	spinlock_t rx_lock;

I think checkpatch wants to have a comment describing the lock.

>  };
>  
>  static LIST_HEAD(isotp_notifier_list);
>  static DEFINE_SPINLOCK(isotp_notifier_lock);
>  static struct isotp_sock *isotp_busy_notifier;
> @@ -613,10 +615,19 @@ static void isotp_rcv(struct sk_buff *skb, void *data)
>  	if (ae && cf->data[0] != so->opt.rx_ext_address)
>  		return;
>  
>  	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.
> +	 *
> +	 * To not lock up the softirq just drop the frame in syzcaller case.
> +	 */
> +	if (!spin_trylock(&so->rx_lock))
> +		return;
> +
>  	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;

Maybe there are more returns, which are not shown in the context of this
patch.

> @@ -666,10 +677,12 @@ static void isotp_rcv(struct sk_buff *skb, void *data)
>  	case N_PCI_CF:
>  		/* rx path: consecutive frame */
>  		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,
>  				 int ae, int off)
>  {
> @@ -1442,10 +1455,11 @@ static int isotp_init(struct sock *sk)
>  	so->rxtimer.function = isotp_rx_timer_handler;
>  	hrtimer_init(&so->txtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
>  	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);
>  	spin_unlock(&isotp_notifier_lock);

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
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