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

From: Daniel Borkmann <[email-masked]>
Date: Sat, 07 Dec 2013 13:43:49 +0100

On 12/07/2013 08:17 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]>
> ---

Thanks Wang, also for your second patch.

Second one looks good to me, thanks for the cleanup!

I was wondering where 86400000 comes from? Looking through the git
history didn't give much clues and the RFC4960 neither. Clearly,
section 15 of RFC4960 *recommends* as initial values ...

   RTO.Initial - 3 seconds
   RTO.Min - 1 second
   RTO.Max - 60 seconds

... which we have as constants in [1] and are assigned to globals
initially in [2,3] with those recommended values. That's all good.

But still [not *directly* related to your patch though], where does
86400000 come from? I expect that's for the max SCTP heartbeat
interval or max cookie lifetime?

Hence, timer_max is used in multiple contexts for timers here,
which seems a bit confusing. If it really makes sense to have such
a huge RTO max though, then it at least needs a comment explaining
so. ;)

Wang, just a minor nitpick, I would much rather name them those
defines like ...

   SCTP_RTO_MIN_LIMIT
   SCTP_RTO_MAX_LIMIT

... just so that we have recommended and upper limit constants with
a more clear naming as obviously SCTP_ONE doesn't make much sense.

  [1] include/net/sctp/constants.h +269
  [2] include/net/netns/sctp.h +39
  [3] net/sctp/protocol.c +1169

More below ...

>   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;
> +
>   	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;

So here, I'd do something like this ...

static int one = 1;              (leaving this as is)
static int timer_max = 86400000; /* Max 1 day for HB interval, cookie life-time*/

static int rto_timer_min = SCTP_RTO_MIN_LIMIT;
static int rto_timer_max = SCTP_RTO_MAX_LIMIT;

... so that we have sack_timer_{min,max} and rto_timer_{min,max}.

Opinions, thoughts?

>   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;
>