netdev - Re: [PATCH] can: bcm: check timer values before ktime conversion

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Date:   Sat, 12 Jan 2019 23:45:29 +0100
From:   Andre Naujoks <nautsch2@...il.com>
To:     Oliver Hartkopp <socketcan@...tkopp.net>, davem@...emloft.net,
        netdev@...r.kernel.org
Cc:     linux-can@...r.kernel.org, lifeasageek@...il.com,
        threeearcat@...il.com, syzkaller@...glegroups.com,
        Kyungtae Kim <kt0755@...il.com>,
        linux-stable <stable@...r.kernel.org>
Subject: Re: [PATCH] can: bcm: check timer values before ktime conversion

I really don't know. That's why I'd be hesitant to restrict this. Maybe
limit it to something really out of the ordinary, like a year?

I am not sure that for example one hour would be out of the question for
some edge cases. Maybe someone wants to do a heartbeat for his/her
system with a very low priority. This would mean a TX_SETUP with a
timeout of an hour and a RX_SETUP with a timeout of a bit more.

If the system allow timeouts in those ranges, I think it should be
allowed. If someone wants to wait a year for a CAN frame, however
unlikely that might be, why not?

Andre.

On 1/12/19 11:30 PM, Oliver Hartkopp wrote:
> Hi Andre,
> 
> just wondered whether it makes sense to limit this value for sending
> cyclic messages or for detecting a timeout on reception.
> 
> 4.294.967.295 seconds would be ~136 years - this makes no sense to me
> and I would assume someone applied some (unintended?) stuff into the
> timeval.
> 
> Don't you think?
> 
> Best,
> Oliver
> 
> On 1/12/19 11:16 PM, Andre Naujoks wrote:
>> Hi.
>>
>> The 15 minute limit seems arbitrary to me. I'd be surprised if an
>> (R|T)X_SETUP failed because of a timeout greater than this. Are there
>> any problems with allowing larger timeouts? If not, I do not see a
>> reason to restrict this.
>>
>> Regards
>>    Andre
>>
>> On 1/12/19 10:57 PM, Oliver Hartkopp wrote:
>>> Kyungtae Kim detected a potential integer overflow in
>>> bcm_[rx|tx]_setup() when
>>> the conversion into ktime multiplies the given value with
>>> NSEC_PER_USEC (1000).
>>>
>>> Reference: https://marc.info/?l=linux-can&m=154732118819828&w=2
>>>
>>> Add a check for the given tv_usec, so that the value stays below one
>>> second.
>>> Additionally limit the tv_sec value to a reasonable value for CAN
>>> related
>>> use-cases of 15 minutes.
>>>
>>> Reported-by: Kyungtae Kim <kt0755@...il.com>
>>> Tested-by: Oliver Hartkopp <socketcan@...tkopp.net>
>>> Signed-off-by: Oliver Hartkopp <socketcan@...tkopp.net>
>>> Cc: linux-stable <stable@...r.kernel.org> # >= 2.6.26
>>> ---
>>>   net/can/bcm.c | 23 +++++++++++++++++++++++
>>>   1 file changed, 23 insertions(+)
>>>
>>> diff --git a/net/can/bcm.c b/net/can/bcm.c
>>> index 0af8f0db892a..ff3799be077b 100644
>>> --- a/net/can/bcm.c
>>> +++ b/net/can/bcm.c
>>> @@ -67,6 +67,9 @@
>>>    */
>>>   #define MAX_NFRAMES 256
>>>   +/* limit timers to 15 minutes for sending/timeouts */
>>> +#define BCM_TIMER_SEC_MAX (15*60)
>>> +
>>>   /* use of last_frames[index].flags */
>>>   #define RX_RECV    0x40 /* received data for this element */
>>>   #define RX_THR     0x80 /* element not been sent due to throttle
>>> feature */
>>> @@ -140,6 +143,18 @@ static inline ktime_t
>>> bcm_timeval_to_ktime(struct bcm_timeval tv)
>>>       return ktime_set(tv.tv_sec, tv.tv_usec * NSEC_PER_USEC);
>>>   }
>>>   +/* check limitations for timeval provided by user */
>>> +static int bcm_is_invalid_tv(struct bcm_msg_head *msg_head)
>>> +{
>>> +    if ((msg_head->ival1.tv_sec > BCM_TIMER_SEC_MAX) ||
>>> +        (msg_head->ival1.tv_usec >= USEC_PER_SEC) ||
>>> +        (msg_head->ival2.tv_sec > BCM_TIMER_SEC_MAX) ||
>>> +        (msg_head->ival2.tv_usec >= USEC_PER_SEC))
>>> +        return 1;
>>> +
>>> +    return 0;
>>> +}
>>> +
>>>   #define CFSIZ(flags) ((flags & CAN_FD_FRAME) ? CANFD_MTU : CAN_MTU)
>>>   #define OPSIZ sizeof(struct bcm_op)
>>>   #define MHSIZ sizeof(struct bcm_msg_head)
>>> @@ -873,6 +888,10 @@ static int bcm_tx_setup(struct bcm_msg_head
>>> *msg_head, struct msghdr *msg,
>>>       if (msg_head->nframes < 1 || msg_head->nframes > MAX_NFRAMES)
>>>           return -EINVAL;
>>>   +    /* check timeval limitations */
>>> +    if ((msg_head->flags & SETTIMER) && bcm_is_invalid_tv(msg_head))
>>> +        return -EINVAL;
>>> +
>>>       /* check the given can_id */
>>>       op = bcm_find_op(&bo->tx_ops, msg_head, ifindex);
>>>       if (op) {
>>> @@ -1053,6 +1072,10 @@ static int bcm_rx_setup(struct bcm_msg_head
>>> *msg_head, struct msghdr *msg,
>>>            (!(msg_head->can_id & CAN_RTR_FLAG))))
>>>           return -EINVAL;
>>>   +    /* check timeval limitations */
>>> +    if ((msg_head->flags & SETTIMER) && bcm_is_invalid_tv(msg_head))
>>> +        return -EINVAL;
>>> +
>>>       /* check the given can_id */
>>>       op = bcm_find_op(&bo->rx_ops, msg_head, ifindex);
>>>       if (op) {
>>>
>>