Subject: Re: [PATCH v5 1/2] sctp: check the rto_min and rto_max

From: Vlad Yasevich <[email-masked]>
Date: Sun, 08 Dec 2013 21:40:15 -0500

On 12/08/2013 09:28 PM, Wang Weidong wrote:
> On 2013/12/9 10:19, Vlad Yasevich wrote:
>> On 12/08/2013 08:53 PM, Wang Weidong wrote:
>>> On 2013/12/8 2:54, Vlad Yasevich wrote:
>>>> On 12/07/2013 02:17 AM, Wang Weidong wrote:
>>>>> rto_min should be smaller than rto_max while rto_max should be larger
>>>>> than rto_min. Add two proc_handler for the checking. Add the check in
>>>>> sctp_setsockopt_rtoinfo.
>>>>>
>>>>> Suggested-by: Vlad Yasevich <[email-masked]>
>>>>> Signed-off-by: Wang Weidong <[email-masked]>
>>>>> ---
>>>>>  include/net/sctp/constants.h |  3 ++
>>>>>  net/sctp/socket.c            |  5 +++
>>>>>  net/sctp/sysctl.c            | 73 ++++++++++++++++++++++++++++++++++++++++----
>>>>>  3 files changed, 75 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/include/net/sctp/constants.h b/include/net/sctp/constants.h
>>>>> index 2f0a565..d276978 100644
>>>>> --- a/include/net/sctp/constants.h
>>>>> +++ b/include/net/sctp/constants.h
>>>>> @@ -279,6 +279,9 @@ enum { SCTP_MAX_GABS = 16 };
>>>>>  #define SCTP_RTO_ALPHA          3   /* 1/8 when converted to right shifts. */
>>>>>  #define SCTP_RTO_BETA           2   /* 1/4 when converted to right shifts. */
>>>>>  
>>>>> +#define SCTP_ONE                1        /* 1 ms */
>>>>> +#define SCTP_TIMER_MAX          86400000 /* ms in one day */
>>>>> +
>>>>>  /* Maximum number of new data packets that can be sent in a burst.  */
>>>>>  #define SCTP_DEFAULT_MAX_BURST		4
>>>>>  
>>>>> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
>>>>> index 72046b9..13411ad 100644
>>>>> --- a/net/sctp/socket.c
>>>>> +++ b/net/sctp/socket.c
>>>>> @@ -2818,6 +2818,11 @@ static int sctp_setsockopt_rtoinfo(struct sock *sk, char __user *optval, unsigne
>>>>>  	if (copy_from_user(&rtoinfo, optval, optlen))
>>>>>  		return -EFAULT;
>>>>>  
>>>>> +	if (rtoinfo.srto_min < SCTP_ONE ||
>>>>> +	    rtoinfo.srto_max > SCTP_TIMER_MAX ||
>>>>> +	    rtoinfo.srto_max < rtoinfo.srto_min)
>>>>> +		return -EINVAL;
>>>>> +
>>>>
>>>> You can not do the check for srto_min < 1.  The following is the text
>>>> from the spec:
>>>>    All times are given in milliseconds.  A value of 0, when modifying
>>>>    the parameters, indicates that the current value should not be
>>>>    changed.
>>>>
>>> Yes, Your are right, I found it in draft-ietf-tsvwg-sctpsocket-14.txt.
>>> Thanks.
>>>
>>>> So, it is valid for a user to pass in a value of 0.  Also, I am not sure
>>>> if it makes sense to bind the upper limit here, as well.
>>>>
>>>> -vlad
>>>>
>>> Here, I am not sure as well. I think it should like what we do to the
>>> init_net.sctp.rto_max when set larger than timer_max. Just not change the value.
>>>
>>
>> So, the basic reason that sysctl is limited is that it is a default
>> for all sctp association on the system.  It makes some sense to limit
>> what the max value here could be.  Limiting it to double suggested
>> RTO.MAX would only make it 2 minutes and may be insufficient for some
>> of the high latency low-throughput wireless links.  Making it about an
>> hour should be fine...  This would be a separate patch though...
>>
> Here, you mean that we should use 3600*1000 rather than 86400000? So
> we should use another patch to fix that after my patchs?
> 
>> Limiting the user-supplied value is not as appropriate since the
>> assumption is that user application may know better what it's
>> requirements are and it is not up to the stack to limit those.  As
>> long as the user value is withing the usable range (and the kernel
>> will already knows how and does limit this range), we should not
>> limit this further.
>>
>> -vlad
>>
> Agree, So I should check like this:
> !srto_min || !srto_max || srto_min > srto_max ?
> And no need to add macros for checking.

No, I think this would have to be a little more complicated :(
Remember it's ok to have srto_min == 0 and srto_max == 0.  It just
means that no change happens.

You may need to do something like

  unsigned long rto_max, rto_min;

  if (rtoinfo.srto_max)
     rto_max = msecs_to_jiffies(rtoinfo.srto_max);
  else
     rto_max = asoc ? asoc->rto_max : sp->rto_max;

  if (rtoinfo.srto_min)
     rto_min = msecs_to_jiffies(rtoinfo.srto_min);
  else
     rto_min = asoc ? asoc->rto_min : sp->rto_min;

  if (rto_min > rto_max)
      return -EINVAL;

  if (asoc) {
      asoc->rto_min = rto_min;
      asoc->rto_max = rto_max;
   ...
   etc....

This way we make sure that the user that supplied just rto_min or just
rto_max didn't set them so that min > max.

-vlad
> 
> Thanks.
> 
>>>
>>> Regards.
>>> Wang
>>>
>>>>>  	asoc = sctp_id2assoc(sk, rtoinfo.srto_assoc_id);
>>>>>  
>>>>>  	/* Set the values to the specific association */
>>>>> diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
>>>>> index 6b36561..33c56c6 100644
>>>>> --- a/net/sctp/sysctl.c
>>>>> +++ b/net/sctp/sysctl.c
>>>>> @@ -40,8 +40,8 @@
>>>>>  #include <linux/sysctl.h>
>>>>>  
>>>>>  static int zero = 0;
>>>>> -static int one = 1;
>>>>> -static int timer_max = 86400000; /* ms in one day */
>>>>> +static int one = SCTP_ONE;
>>>>> +static int timer_max = SCTP_TIMER_MAX;
>>>>>  static int int_max = INT_MAX;
>>>>>  static int sack_timer_min = 1;
>>>>>  static int sack_timer_max = 500;
>>>>> @@ -61,6 +61,13 @@ static int proc_sctp_do_hmac_alg(struct ctl_table *ctl,
>>>>>  				void __user *buffer, size_t *lenp,
>>>>>  
>>>>>  				loff_t *ppos);
>>>>> +static int proc_sctp_do_rto_min(struct ctl_table *ctl, int write,
>>>>> +				void __user *buffer, size_t *lenp,
>>>>> +				loff_t *ppos);
>>>>> +static int proc_sctp_do_rto_max(struct ctl_table *ctl, int write,
>>>>> +				void __user *buffer, size_t *lenp,
>>>>> +				loff_t *ppos);
>>>>> +
>>>>>  static struct ctl_table sctp_table[] = {
>>>>>  	{
>>>>>  		.procname	= "sctp_mem",
>>>>> @@ -102,17 +109,17 @@ static struct ctl_table sctp_net_table[] = {
>>>>>  		.data		= &init_net.sctp.rto_min,
>>>>>  		.maxlen		= sizeof(unsigned int),
>>>>>  		.mode		= 0644,
>>>>> -		.proc_handler	= proc_dointvec_minmax,
>>>>> +		.proc_handler	= proc_sctp_do_rto_min,
>>>>>  		.extra1         = &one,
>>>>> -		.extra2         = &timer_max
>>>>> +		.extra2         = &init_net.sctp.rto_max
>>>>>  	},
>>>>>  	{
>>>>>  		.procname	= "rto_max",
>>>>>  		.data		= &init_net.sctp.rto_max,
>>>>>  		.maxlen		= sizeof(unsigned int),
>>>>>  		.mode		= 0644,
>>>>> -		.proc_handler	= proc_dointvec_minmax,
>>>>> -		.extra1         = &one,
>>>>> +		.proc_handler	= proc_sctp_do_rto_max,
>>>>> +		.extra1         = &init_net.sctp.rto_min,
>>>>>  		.extra2         = &timer_max
>>>>>  	},
>>>>>  	{
>>>>> @@ -342,6 +349,60 @@ static int proc_sctp_do_hmac_alg(struct ctl_table *ctl,
>>>>>  	return ret;
>>>>>  }
>>>>>  
>>>>> +static int proc_sctp_do_rto_min(struct ctl_table *ctl, int write,
>>>>> +				void __user*buffer, size_t *lenp,
>>>>> +				loff_t *ppos)
>>>>> +{
>>>>> +	struct net *net = current->nsproxy->net_ns;
>>>>> +	int new_value;
>>>>> +	struct ctl_table tbl;
>>>>> +	unsigned int min = *(unsigned int *) ctl->extra1;
>>>>> +	unsigned int max = *(unsigned int *) ctl->extra2;
>>>>> +	int ret;
>>>>> +
>>>>> +	memset(&tbl, 0, sizeof(struct ctl_table));
>>>>> +	tbl.maxlen = sizeof(unsigned int);
>>>>> +
>>>>> +	if (write)
>>>>> +		tbl.data = &new_value;
>>>>> +	else
>>>>> +		tbl.data = &net->sctp.rto_min;
>>>>> +	ret = proc_dointvec(&tbl, write, buffer, lenp, ppos);
>>>>> +	if (write) {
>>>>> +		if (ret || new_value > max || new_value < min)
>>>>> +			return -EINVAL;
>>>>> +		net->sctp.rto_min = new_value;
>>>>> +	}
>>>>> +	return ret;
>>>>> +}
>>>>> +
>>>>> +static int proc_sctp_do_rto_max(struct ctl_table *ctl, int write,
>>>>> +				void __user*buffer, size_t *lenp,
>>>>> +				loff_t *ppos)
>>>>> +{
>>>>> +	struct net *net = current->nsproxy->net_ns;
>>>>> +	int new_value;
>>>>> +	struct ctl_table tbl;
>>>>> +	unsigned int min = *(unsigned int *) ctl->extra1;
>>>>> +	unsigned int max = *(unsigned int *) ctl->extra2;
>>>>> +	int ret;
>>>>> +
>>>>> +	memset(&tbl, 0, sizeof(struct ctl_table));
>>>>> +	tbl.maxlen = sizeof(unsigned int);
>>>>> +
>>>>> +	if (write)
>>>>> +		tbl.data = &new_value;
>>>>> +	else
>>>>> +		tbl.data = &net->sctp.rto_max;
>>>>> +	ret = proc_dointvec(&tbl, write, buffer, lenp, ppos);
>>>>> +	if (write) {
>>>>> +                if (ret || new_value > max || new_value < min)
>>>>> +			return -EINVAL;
>>>>> +		net->sctp.rto_max = new_value;
>>>>> +	}
>>>>> +	return ret;
>>>>> +}
>>>>> +
>>>>>  int sctp_sysctl_net_register(struct net *net)
>>>>>  {
>>>>>  	struct ctl_table *table;
>>>>>
>>>>
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> 
>