kern/112670: [if_tap] stat /dev/tapN leads to panic for N >= 2G

[Remko Lodder]

The following reply was made to PR kern/112670; it has been noted by GNATS.

From: Remko Lodder <remko at elvandar.org>
To: Ludovico Gardenghi <osd at cs.unibo.it>
Cc: freebsd-gnats-submit at FreeBSD.org
Subject: Re: kern/112670: [if_tap] stat /dev/tapN leads to panic for N >=
 2G
Date: Tue, 15 May 2007 20:08:05 +0200

 Ludovico Gardenghi wrote:
 >> Number:         112670
 >> Category:       kern
 >> Synopsis:       [if_tap] stat /dev/tapN leads to panic for N >= 2G
 >> Confidential:   no
 >> Severity:       serious
 >> Priority:       medium
 >> Responsible:    freebsd-bugs
 >> State:          open
 >> Quarter:        
 >> Keywords:       
 >> Date-Required:
 >> Class:          sw-bug
 >> Submitter-Id:   current-users
 >> Arrival-Date:   Mon May 14 23:00:11 GMT 2007
 >> Closed-Date:
 >> Last-Modified:
 >> Originator:     Ludovico Gardenghi
 >> Release:        6.2-RELEASE
 >> Organization:
 > Virtual Square Team
 >> Environment:
 > FreeBSD devil.localdomain 6.2-RELEASE FreeBSD 6.2-RELEASE #0: Fri Jan 12 10:40:27 UTC 2007     root at dessler.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386
 >> Description:
 > Trying to access a tap device in /dev leads to a kernel panic ("foo") if the tap name is tapN when N is greater or equal than 2^31 and less than 2^32-1. 
 > 
 > This is probably due to a bad conversion between unsigned and signed in dev_stdclone (kern_conf.c:750). The tap name is converted from string to integer with a loop (lines 762--765) and stored in the signed int variable 'u'; if the resulting value is greater than 2G, u becomes negative and the check at line 766 (if (u > 0xffffff)) fails, but the original value is in fact greater than that value and should be rejected.
 >> How-To-Repeat:
 > shammash at devil:~$ ls -l /dev/tap2147483648
 > 
 > (the following is in /var/log/messages)
 > 
 > May 10 13:57:12 devil kernel: dev 0xc370a000 (tap-1530494977) is on clonelist
 > May 10 13:57:12 devil kernel: unit=-1530494977, low=0, extra=0x0
 > May 10 13:57:12 devil kernel: 0xc36b4b00 tap0
 > May 10 13:57:12 devil kernel: 0xc36f1500 tap255
 > May 10 13:57:12 devil kernel: 0xc34f2000 tap256
 > May 10 13:57:12 devil kernel: 0xc32aee00 tap65537
 > May 10 13:57:12 devil kernel: 0xc36f1a00 tap1
 > May 10 13:57:12 devil kernel: 0xc36f1600 tap2
 > May 10 13:57:12 devil kernel: 0xc370a000 tap-1530494977
 > May 10 13:57:12 devil kernel: panic: foo
 > May 10 13:57:12 devil kernel: Uptime: 35m24s
 > May 10 13:57:12 devil kernel: Cannot dump. No dump device defined.
 > May 10 13:57:12 devil kernel: Automatic reboot in 15 seconds - press a key on the console to abort
 > May 10 13:57:12 devil kernel: Rebooting...
 >> Fix:
 > It should be enough to change 'int' to 'unsigned int' inside the functions involved in tap creation, mainly dev_stdclone() in kern/kern_conf.c. 
 >> Release-Note:
 >> Audit-Trail:
 >> Unformatted:
 > _______________________________________________
 > freebsd-bugs at freebsd.org mailing list
 > http://lists.freebsd.org/mailman/listinfo/freebsd-bugs
 > To unsubscribe, send any mail to "freebsd-bugs-unsubscribe at freebsd.org"
 
 Can you try obtaining us a kernel dump as mentioned in the developers
 handbook?
 
 Thanks!
 
 -- 
 Kind regards,
 
      Remko Lodder               ** remko at elvandar.org
      FreeBSD                    ** remko at FreeBSD.org
 
      /* Quis custodiet ipsos custodes */