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

[Ludovico Gardenghi]

>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: