Hi,
My apologies, I forgot to include the actual patch. Duh.
-Myrdraal
-- Linux jackalz 2.1.108 #77 Sat Jun 27 00:55:49 EDT 1998 i486 5:55am up 4:24, 15 users, load average: 0.69, 0.47, 0.37--FkmkrVfFsRoUs1wW Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="sysrq_enable-2.1.107.diff"
diff -ur linpatch/Documentation/sysrq.txt linux/Documentation/sysrq.txt --- linpatch/Documentation/sysrq.txt Sat Jun 27 05:25:53 1998 +++ linux/Documentation/sysrq.txt Sat Jun 27 05:35:43 1998 @@ -1,6 +1,6 @@ - MAGIC SYSRQ KEY DOCUMENTATION v1.2 + MAGIC SYSRQ KEY DOCUMENTATION v1.3 ------------------------------------ - [Sat May 16 01:09:21 EDT 1998] + [Sat Jun 27 05:35:38 EDT 1998] * What is the magic SysRQ key? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -104,6 +104,24 @@ '#define SYSRQ_KEY 0x54' in [/usr/src/linux/]include/asm/keyboard.h to the keycode of the key you wish to use, then recompile. Oh, and by the way, you exit 'showkey' by not typing anything for ten seconds. + +* Is SysRQ a security hazard? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Well, I just told you the things you can do with it - judge for yourself. :) +It's likely that someone with access to the console of the machine could do +evil things with mostly the same effect. (Why hit ALT-SysRQ-B when you can +just slam the reset switch?) There are probably some circumstances where this +is not true (a well protected public access machine, perhaps.), but I think +for the majority of systems SysRQ is very useful. + +* Can I toggle SysRQ without recompiling and rebooting? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Yes, provided you compiled in support for the magic SysRQ key. +echo "0" >/proc/sys/debug/sysrq_enable +The above will disable the magic SysRQ key. +echo "1" >/proc/sys/debug/sysrq_enable +The above will enable the magic SysRQ key. The magic SysRQ key defaults to +being on at boot. * I have more questions, who can I ask? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ diff -ur linpatch/drivers/char/sysrq.c linux/drivers/char/sysrq.c --- linpatch/drivers/char/sysrq.c Thu Jun 25 01:10:11 1998 +++ linux/drivers/char/sysrq.c Thu Jun 25 06:50:43 1998 @@ -27,6 +27,8 @@ #include <linux/apm_bios.h> #endif +int sysctl_sysrq_enable = 1; + extern void wakeup_bdflush(int); extern void reset_vc(unsigned int); extern int console_loglevel; @@ -57,7 +59,7 @@ { int orig_log_level = console_loglevel; - if (!key) + if (!key || !sysctl_sysrq_enable) return; console_loglevel = 7; diff -ur linpatch/include/linux/sysctl.h linux/include/linux/sysctl.h --- linpatch/include/linux/sysctl.h Thu Jun 25 01:09:30 1998 +++ linux/include/linux/sysctl.h Thu Jun 25 06:50:43 1998 @@ -369,6 +369,9 @@ }; /* CTL_DEBUG names: */ +enum { + DEBUG_SYSRQ_ENABLE = 1, +}; /* CTL_DEV names: */ enum { diff -ur linpatch/kernel/sysctl.c linux/kernel/sysctl.c --- linpatch/kernel/sysctl.c Thu Jun 25 01:10:37 1998 +++ linux/kernel/sysctl.c Thu Jun 25 06:50:43 1998 @@ -41,6 +41,9 @@ extern int bdf_prm[], bdflush_min[], bdflush_max[]; extern char binfmt_java_interpreter[], binfmt_java_appletviewer[]; extern int sysctl_overcommit_memory; +#ifdef CONFIG_MAGIC_SYSRQ +extern int sysctl_sysrq_enable; +#endif #ifdef CONFIG_KMOD extern char modprobe_path[]; #endif @@ -236,6 +239,10 @@ }; static ctl_table debug_table[] = { +#ifdef CONFIG_MAGIC_SYSRQ + {DEBUG_SYSRQ_ENABLE, "sysrq_enable", &sysctl_sysrq_enable, sizeof(int), + 0644, NULL, &proc_dointvec}, +#endif {0} };
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