Re: [PATCH] NET:AX25:ROSE NULL ax25_cb kernel panic

[f6bvp <f6bvp@free.fr>]

Dimitri,

I am so pleased to get some support for fixing this bug that I will let
you manage things as you like.
Please perform necessary actions for proper achievement of our concern.
You have my approbation for any change you think is needed.

Regards,

Bernard


Le 20/01/2019 à 11:32, Dmitry Vyukov a écrit :
> On Sun, Jan 20, 2019 at 10:58 AM f6bvp <f6bvp@free.fr> wrote:
>>
>> Hi,
>>
>> Dmitry wrote:
>>
>>> Please also add:
>>> Reported-by: syzbot+1a2c456a1ea08fa5b5f7@syzkaller.appspotmail.com
>>
>> I did mention syzbot report but without the exact reference, thanks.
>>
>>> It's this report we are fixing, right?
>>> https://syzkaller.appspot.com/bug?id=fd0b0b00fc26abb4b35663a0e2f1c91d8e6e5725
>>
>> Yes exactly !
>> This is a long date well know bug I reported two years ago.
> 
> Then, well, I don't know, we either can leave syzbot as reporter if
> you don't mind. Or don't include it as supports other means to
> associate reports with fixes (#syz fix tag in email). The goal of
> associating fixes with reports is to "close" bugs and get them off the
> dashboard:
> https://syzkaller.appspot.com/#upstream-open
> Otherwise it turns into unuseful pile of bugs.
> 
> 
> 
>> Bernard
>>
>>
>> On Sat, Jan 19, 2019 at 11:58 AM f6bvp <f6bvp@free.fr> wrote:
>>>
>>>
>>> [PATCH] [ROSE] NULL ax25_cb kernel panic
>>>
>>> When an internally generated frame is handled by rose_xmit(),
>>> rose_route_frame() is called:
>>>
>>>         if (!rose_route_frame(skb, NULL)) {
>>>                 dev_kfree_skb(skb);
>>>                 stats->tx_errors++;
>>>                 return NETDEV_TX_OK;
>>>         }
>>>
>>> We have the same code sequence in Net/Rom where an internally generated
>>> frame is handled by nr_xmit() calling nr_route_frame(skb, NULL).
>>> However, in this function NULL argument is tested while it is not in
>>> rose_route_frame().
>>> Then kernel panic occurs later on when calling ax25cmp() with a NULL
>>> ax25_cb argument as reported many times and recently with syzbot.
>>>
>>> We need to test if ax25 is NULL before using it.
>>>
>>> Here is the patch:
>>>
>>> diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
>>> index 77e9f85a2c92..7f075255a372 100644
>>> --- a/net/rose/rose_route.c
>>> +++ b/net/rose/rose_route.c
>>> @@ -850,6 +850,7 @@ void rose_link_device_down(struct net_device *dev)
>>>
>>>  /*
>>>   *     Route a frame to an appropriate AX.25 connection.
>>> + *     a NULL ax25_cb indicates an internally generated frame.
>>>   */
>>>  int rose_route_frame(struct sk_buff *skb, ax25_cb *ax25)
>>>  {
>>> @@ -867,6 +868,10 @@ int rose_route_frame(struct sk_buff *skb, ax25_cb
>>> *ax25)
>>>
>>>         if (skb->len < ROSE_MIN_LEN)
>>>                 return res;
>>> +
>>> +       if (!ax25)
>>> +               return rose_loopback_queue(skb, NULL);
>>> +
>>>         frametype = skb->data[2];
>>>         lci = ((skb->data[0] << 8) & 0xF00) + ((skb->data[1] << 0) &
>> 0x0FF);
>>>         if (frametype == ROSE_CALL_REQUEST &&
>>>
>>> Signed-off-by: Bernard Pidoux, f6bvp <f6bvp@free.fr>
>>
>> Please also add:
>>
>> Reported-by: syzbot+1a2c456a1ea08fa5b5f7@syzkaller.appspotmail.com
>>
>> It's this report we are fixing, right?
>> https://syzkaller.appspot.com/bug?id=fd0b0b00fc26abb4b35663a0e2f1c91d8e6e5725