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

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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@xxxxxxxxx>
Tested-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
Cc: linux-stable <stable@xxxxxxxxxxxxxxx> # >= 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) {





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