Date: Sat, 28 Jun 2008 23:47:09 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: Ivaylo Mateev <mateev@cns-consulting.org> Cc: hackers@freebsd.org Subject: Re: Securelevels Message-ID: <20080629044709.GA76555@dan.emsphone.com> In-Reply-To: <200806290313.21720.mateev@cns-consulting.org> References: <200806290313.21720.mateev@cns-consulting.org>
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In the last episode (Jun 29), Ivaylo Mateev said:
> I think I found a bug.
>
> [strato@darkstar /usr/home/strato]$ sudo sysctl kern.securelevel
> kern.securelevel: 2
> [strato@darkstar /usr/home/strato]$ kgdb
> kgdb: /dev/mem: Permission denied
> [strato@darkstar /usr/home/strato]$ sudo kgdb
> [GDB will not be able to debug user-mode threads: /usr/lib/libthread_db.so:
> Undefined symbol "ps_pglobal_lookup"]
> GNU gdb 6.1.1 [FreeBSD]
>
> I am running in securelevel 2. That means nithing can have direct access
> to /dev/mem, acording to man security:
>
> 1 Secure mode - the system immutable and system append-only flags may
> not be turned off; disks for mounted file systems, /dev/mem and
> /dev/kmem may not be opened for writing; /dev/io (if your platform
> has it) may not be opened at all; kernel modules (see kld(4)) may
> not be loaded or unloaded.
>
> 2 Highly secure mode - same as secure mode, plus disks may not be
> opened for writing (except by mount(2)) whether mounted or not.
> This level precludes tampering with file systems by unmounting
> them, but also inhibits running newfs(8) while the system is multi-
> user.
# truss kgdb < /dev/null |& grep /dev/mem
open("/dev/mem",O_RDONLY,00) = 4 (0x4)
#
Read-only opens of /dev/mem are allowed. "kgdb -w" should fail,
however.
--
Dan Nelson
dnelson@allantgroup.com
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