linux-kernel - Re: general protection fault in can_rx

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Date:   Tue, 21 Jan 2020 09:35:59 +0100
From:   Kurt Van Dijck <dev.kurt@...dijck-laurijssen.be>
To:     Oliver Hartkopp <socketcan@...tkopp.net>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        o.rempel@...gutronix.de,
        syzbot <syzbot+c3ea30e1e2485573f953@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>, linux-can@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: general protection fault in can_rx_register

On di, 21 jan 2020 09:30:35 +0100, Kurt Van Dijck wrote:
> On ma, 20 jan 2020 23:35:16 +0100, Oliver Hartkopp wrote:
> > 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.
> 
> Maybe I got completely lost:
> Shouldn't can_ml_priv and vxcan_priv not be similar?
> Where is the dev_rcv_lists in the vxcan case?

IMHO, net/can/af_can.c:306 is wrong in the vxcan case.

> 
> > 
> > Best regards,
> > Oliver