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

From: Vlad Yasevich <[email-masked]>
Date: Sun, 08 Dec 2013 21:19:00 -0500

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...

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

> 
> 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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>>
> 
>