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Date: Tue, 29 Mar 2005 20:40:35 GMT
From: Anjali Kulkarni <anjali@juniper.net>
To: freebsd-gnats-submit@FreeBSD.org
Subject: When looking for an unused port number for bind or connect, if low & high port range are equal, kernel can trap in divide by zero error
X-Send-Pr-Version: www-2.3

>Number:         79342
>Category:       kern
>Synopsis:       [patch] When looking for an unused port number for bind or connect, if low & high port range are equal, kernel can trap in divide by zero error
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    maxim
>State:          closed
>Quarter:        
>Keywords:       
>Date-Required:  
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Mar 29 20:50:01 GMT 2005
>Closed-Date:    Fri Apr 22 08:10:28 GMT 2005
>Last-Modified:  Fri Apr 22 08:10:28 GMT 2005
>Originator:     Anjali Kulkarni
>Release:        4.10
>Organization:
Juniper Networks
>Environment:
4.10-RELEASE-p2
>Description:
In src/sys/netinet/in_pcb.c, in the function in_pcbbind(), when trying to find an unused port number in the range of ports allowed to be used, there are cases to handle upper port limit > lower port limit and upper port limit < lower port limit, but no case to handle when they are equal. Consequently, if they are equal, the kernel will have a divide by zero trap when the line 
*lastport = first - (arc4random() % (first - last)) 
OR the line
*lastport = first + (arc4random() % (last - first))
is executed, where first and last are the port ranges in which we check for an unused port number.

>How-To-Repeat:

set

net.inet.ip.portrange.first = net.inet.ip.portrange.last. (say 1024)

Now do a bind or a connect with a port number of 0.
>Fix:
In in_pcbbind(), there should be a check for the case when first & last are equal as follows:
                /*
                 * Simple check to ensure all ports are not used up causing
                 * a deadlock here.
                 *
                 * We split the two cases (up and down) so that the direction
                 * is not being tested on each round of the loop.   
                 */
+                 if (first == last) {
+                         inp->inp_laddr.s_addr = INADDR_ANY;
+                         return (EADDRNOTAVAIL);
+                 } else if (first > last) {
-                 if (first > last) {


>Release-Note:
>Audit-Trail:

From: Maxim Konovalov <maxim@macomnet.ru>
To: Anjali Kulkarni <anjali@juniper.net>
Cc: silby@freebsd.org, bug-followup@freebsd.org
Subject: Re: kern/79342: When looking for an unused port number for bind or
 connect, if low & high port range are equal, kernel can trap in divide by
 zero error
Date: Wed, 30 Mar 2005 08:37:19 +0400 (MSD)

 Hi,
 
 > >Synopsis:  When looking for an unused port number for bind or
 > >connect, if low & high port range are equal, kernel can trap in
 > >divide by zero error
 [...]
 > >Release:        4.10
 [...]
 > In src/sys/netinet/in_pcb.c, in the function in_pcbbind(), when
 > trying to find an unused port number in the range of ports allowed
 > to be used, there are cases to handle upper port limit > lower port
 > limit and upper port limit < lower port limit, but no case to handle
 > when they are equal. Consequently, if they are equal, the kernel
 > will have a divide by zero trap when the line *lastport = first -
 > (arc4random() % (first - last)) OR the line *lastport = first +
 > (arc4random() % (last - first)) is executed, where first and last
 > are the port ranges in which we check for an unused port number.
 >
 > >How-To-Repeat:
 >
 > set
 >
 > net.inet.ip.portrange.first = net.inet.ip.portrange.last. (say 1024)
 
 Just a note the bug is appeared with
 net.inet.ip.portrange.randomized=1 only.
 
 I think we need to stop doing random port allocation if last - first
 delta is ridiculous small.
 
 -- 
 Maxim Konovalov

From: Maxim Konovalov <maxim@macomnet.ru>
To: Anjali Kulkarni <anjali@juniper.net>
Cc: silby@freebsd.org, bug-followup@freebsd.org
Subject: Re: kern/79342: When looking for an unused port number for bind or
 connect, if low & high port range are equal, kernel can trap in divide by
 zero error
Date: Wed, 30 Mar 2005 21:18:27 +0400 (MSD)

 > Just a note the bug is appeared with
 > net.inet.ip.portrange.randomized=1 only.
 >
 > I think we need to stop doing random port allocation if last - first
 > delta is ridiculous small.
 
 Here is my version of the patch:
 
 Index: in_pcb.c
 ===================================================================
 RCS file: /home/ncvs/src/sys/netinet/in_pcb.c,v
 retrieving revision 1.161
 diff -u -p -r1.161 in_pcb.c
 --- in_pcb.c	23 Mar 2005 09:26:38 -0000	1.161
 +++ in_pcb.c	30 Mar 2005 16:36:58 -0000
 @@ -411,13 +411,19 @@ in_pcbbind_setup(inp, nam, laddrp, lport
  		 * For UDP, use random port allocation as long as the user
  		 * allows it.  For TCP (and as of yet unknown) connections,
  		 * use random port allocation only if the user allows it AND
 -		 * ipport_tick allows it.
 +		 * ipport_tick() allows it.
  		 */
  		if (ipport_randomized &&
  			(!ipport_stoprandom || pcbinfo == &udbinfo))
  			dorandom = 1;
  		else
  			dorandom = 0;
 +		/*
 +		 * It makes no sense to do random port allocation if
 +		 * we have the only port available.
 +		 */
 +		if (first == last)
 +			dorandom = 0;
  		/* Make sure to not include UDP packets in the count. */
  		if (pcbinfo != &udbinfo)
  			ipport_tcpallocs++;
 %%%
 
 It's not perfect because it should turn random port allocation off if
 the diapason of ports is small but I am not sure yet we need an
 additional sysctl for that.  Mike, what is your opinion?
 
 As a side note for the original PR: random port allocation was broken
 in RELENG_4, that is why we turned it off by default in RELENG_4 some
 time after 4.10-REL and turned it on back right before 4.11-REL when
 Mike implemented a new algorithm.  If you are going to use 4.10-REL
 you need to turn the port randomization off or import Mike's code.
 
 -- 
 Maxim Konovalov

From: Mike Silbersack <silby@silby.com>
To: Maxim Konovalov <maxim@macomnet.ru>
Cc: Anjali Kulkarni <anjali@juniper.net>, bug-followup@freebsd.org
Subject: Re: kern/79342: When looking for an unused port number for bind or
 connect, if low & high port range are equal, kernel can trap in divide by
 zero error
Date: Wed, 30 Mar 2005 14:28:15 -0600 (CST)

 On Wed, 30 Mar 2005, Maxim Konovalov wrote:
 
 > It's not perfect because it should turn random port allocation off if
 > the diapason of ports is small but I am not sure yet we need an
 > additional sysctl for that.  Mike, what is your opinion?
 
 If the port range is very small, turning random port allocation off makes 
 sense.  Since we'll have to do a patch either way, we might as well make 
 that change.
 
 Mike "Silby" Silbersack
State-Changed-From-To: open->patched 
State-Changed-By: maxim 
State-Changed-When: Fri Apr 8 08:44:41 GMT 2005 
State-Changed-Why:  
Fixed in HEAD in a different way, thanks for the report! 


Responsible-Changed-From-To: freebsd-bugs->maxim 
Responsible-Changed-By: maxim 
Responsible-Changed-When: Fri Apr 8 08:44:41 GMT 2005 
Responsible-Changed-Why:  
MFC reminder. 

http://www.freebsd.org/cgi/query-pr.cgi?pr=79342 
State-Changed-From-To: patched->closed 
State-Changed-By: maxim 
State-Changed-When: Fri Apr 22 08:10:11 GMT 2005 
State-Changed-Why:  
Merged to RELENG_5. 

http://www.freebsd.org/cgi/query-pr.cgi?pr=79342 
>Unformatted:
