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Subject: Re: general protection fault in can_rx_register
From:   Oliver Hartkopp <socketcan@hartkopp.net>
To:     Dmitry Vyukov <dvyukov@google.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        o.rempel@pengutronix.de,
        syzbot <syzbot+c3ea30e1e2485573f953@syzkaller.appspotmail.com>,
        David Miller <davem@davemloft.net>, linux-can@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Kurt Van Dijck <dev.kurt@vandijck-laurijssen.be>
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Message-ID: <2a676c0e-20f2-61b5-c72b-f51947bafc7d@hartkopp.net>
Date:   Mon, 20 Jan 2020 23:35:16 +0100
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Answering myself ...

On 20/01/2020 23.02, Oliver Hartkopp wrote:

> 
> Added some code to check whether dev->ml_priv is NULL:
> 
> ~/linux$ git diff
> diff --git a/net/can/af_can.c b/net/can/af_can.c
> index 128d37a4c2e0..6fb4ae4c359e 100644
> --- a/net/can/af_can.c
> +++ b/net/can/af_can.c
> @@ -463,6 +463,10 @@ int can_rx_register(struct net *net, struct 
> net_device *dev, canid_t can_id,
>          spin_lock_bh(&net->can.rcvlists_lock);
> 
>          dev_rcv_lists = can_dev_rcv_lists_find(net, dev);
> +       if (!dev_rcv_lists) {
> +               pr_err("dev_rcv_lists == NULL! %p\n", dev);
> +               goto out_unlock;
> +       }
>          rcv_list = can_rcv_list_find(&can_id, &mask, dev_rcv_lists);
> 
>          rcv->can_id = can_id;
> @@ -479,6 +483,7 @@ int can_rx_register(struct net *net, struct 
> net_device *dev, canid_t can_id,
>          rcv_lists_stats->rcv_entries++;
>          rcv_lists_stats->rcv_entries_max = 
> max(rcv_lists_stats->rcv_entries_max,
> 
> rcv_lists_stats->rcv_entries);
> +out_unlock:
>          spin_unlock_bh(&net->can.rcvlists_lock);
> 
>          return err;
> 
> And the output (after some time) is:
> 
> [  758.505841] netlink: 'crash': attribute type 1 has an invalid length.
> [  758.508045] bond7148: (slave vxcan1): The slave device specified does 
> not support setting the MAC address
> [  758.508057] bond7148: (slave vxcan1): Error -22 calling dev_set_mtu
> [  758.532025] bond10413: (slave vxcan1): The slave device specified 
> does not support setting the MAC address
> [  758.532043] bond10413: (slave vxcan1): Error -22 calling dev_set_mtu
> [  758.532254] dev_rcv_lists == NULL! 000000006b9d257f
> [  758.547392] netlink: 'crash': attribute type 1 has an invalid length.
> [  758.549310] bond7145: (slave vxcan1): The slave device specified does 
> not support setting the MAC address
> [  758.549313] bond7145: (slave vxcan1): Error -22 calling dev_set_mtu
> [  758.550464] netlink: 'crash': attribute type 1 has an invalid length.
> [  758.552301] bond7146: (slave vxcan1): The slave device specified does 
> not support setting the MAC address
> 
> So we can see that we get a ml_priv pointer which is NULL which should 
> not be possible due to this:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/can/dev.c#n743 

This reference doesn't point to the right code as vxcan has its own 
handling do assign ml_priv in vxcan.c .

> Btw. the variable 'size' is set two times at the top of 
> alloc_candev_mqs() depending on echo_skb_max. This looks wrong.

No. It looks right as I did not get behind the ALIGN() macro at first sight.

But it is still open why dev->ml_priv is not set correctly in vxcan.c as 
all the settings for .priv_size and in vxcan_setup look fine.

Best regards,
Oliver