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

From: Vlad Yasevich <[email-masked]>
Date: Sat, 07 Dec 2013 13:54:25 -0500

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.

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

>  	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;
>