Bugtraq mailing list archives
Re: vlock + magic SysRQ key
From: D.Yu.Bolkhovityanov () INP NSK SU (Dmitry Yu. Bolkhovityanov)
Date: Tue, 10 Aug 1999 12:07:25 +0700
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
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