Re: vlock + magic SysRQ key

[D.Yu.Bolkhovityanov () INP NSK SU (Dmitry Yu. Bolkhovityanov)]

On  1 Jan 90 at 5:00, pavel () BUG UCW CZ wrote:

[snip]
> Magic SysRq is in "kernel hacking" section. If you enable it, and you
> are not kernel hacker, you loose. (If you are kernel hacker, you
> certainly don't want mere mortals access your console, do you?
>
> Read help entry:
>
> CONFIG_MAGIC_SYSRQ
>   If you say Y here, you will have some control over the system even
>   if the system crashes for example during kernel debugging (e.g., you
>   will be able to flush the buffer cache to disk, reboot the system
>   immediately or dump some status information). This is accomplished
>   by pressing various keys while holding SysRq (Alt+PrintScreen). The
>   keys are documented in Documentation/sysrq.txt. Don't say Y unless
>                                                   !!!!!!!!!!!!!!!!!!
>   you really know what this hack does.
>   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>
> If you did not realize it allows people to bypass vlock -a, you did
> not know what it does, and you should not have enabled it :-).

    CONFIG_MAGIC_SYSRQ is enabled by default in the 2.2.5 kernel which is
shipped with RedHat-6.0:

viper:/usr/src/linux-2.2.5% grep SYSRQ arch/i386/defconfig .config
arch/i386/defconfig:CONFIG_MAGIC_SYSRQ=y
.config:CONFIG_MAGIC_SYSRQ=y
viper:/usr/src/linux-2.2.5% uname -a
Linux some.inet.address 2.2.5-15 #1 Mon Apr 19 22:21:09 EDT 1999 i586 unknown

    In 2.2.5-22 kernel (the last version in updates/) arch/i386/defconfig has
CONFIG_MAGIC_SYSRQ also enabled.

   The most interesting is that standard kernel distribution
(linux-2.2.5.tar.gz) doesn't have SYSRQ enabled -- it was set to "y" by
RedHat (probably during beta-testing), and is "y" for all architectures.

    So, those who use RedHat don't even have to say "Y" and decide if they
are hackers or not -- the decision was made for them beforehand ;-).
       ___________________________________________________________________
       Dmitry Yu. Bolkhovityanov  |  Novosibirsk, RUSSIA
       phone (383-2)-39-49-56     |  The Budker Institute of Nuclear Physics
                                  |  Lab. 5-13