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

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Message-ID: <1db63586-5ce6-7ec5-f076-ec8d57dffe7d@hartkopp.net>
Date:   Sat, 12 Jan 2019 23:30:41 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Andre Naujoks <nautsch2@...il.com>, 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

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) {
>>
>