Re: Potential DoS attack on PF due to infinite loop

On Wed, Jul 12, 2017 at 02:40:58PM +0200, Alexander Bluhm wrote:
> On Tue, Jul 11, 2017 at 12:29:33PM -0700, Jingmin Zhou wrote:
> > The problem is at line 224. When a LB rule is configured to have 65535 as
> > the high port, and uint16 variable tmp reaches it, ++(tmp) will wrap around
> > and hence potentially enter into an infinite loop. Of course, it only
> > happens when high is configured to 65535.
> 
> I think this should detect all overflow problems.
> 
> ok?

looks good to me.

OK sashan
> 
> bluhm
> 
> Index: net/pf_lb.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/net/pf_lb.c,v
> retrieving revision 1.60
> diff -u -p -r1.60 pf_lb.c
> --- net/pf_lb.c	23 Apr 2017 11:37:11 -0000	1.60
> +++ net/pf_lb.c	12 Jul 2017 12:11:35 -0000
> @@ -211,7 +211,7 @@ pf_get_sport(struct pf_pdesc *pd, struct
>  				return (0);
>  			}
>  		} else {
> -			u_int16_t tmp;
> +			u_int32_t tmp;
>  
>  			if (low > high) {
>  				tmp = low;
> @@ -221,7 +221,7 @@ pf_get_sport(struct pf_pdesc *pd, struct
>  			/* low < high */
>  			cut = arc4random_uniform(1 + high - low) + low;
>  			/* low <= cut <= high */
> -			for (tmp = cut; tmp <= high; ++(tmp)) {
> +			for (tmp = cut; tmp <= high && tmp <= 0xffff; ++tmp) {
>  				key.port[sidx] = htons(tmp);
>  				if (pf_find_state_all(&key, dir, NULL) ==
>  				    NULL && !in_baddynamic(tmp, pd->proto)) {
> @@ -229,7 +229,8 @@ pf_get_sport(struct pf_pdesc *pd, struct
>  					return (0);
>  				}
>  			}
> -			for (tmp = cut - 1; tmp >= low; --(tmp)) {
> +			tmp = cut;
> +			for (tmp -= 1; tmp >= low && tmp <= 0xffff; --tmp) {
>  				key.port[sidx] = htons(tmp);
>  				if (pf_find_state_all(&key, dir, NULL) ==
>  				    NULL && !in_baddynamic(tmp, pd->proto)) {
>