[881] in bugtraq
Re: MAGIC PIDs (was Re: magic??)
daemon@ATHENA.MIT.EDU (Reto Lichtensteiger)
Thu Feb 2 20:34:29 1995
From: Reto Lichtensteiger <rali@hri.com>
To: shipley@merde.dis.org (Pete Shipley)
Date: Thu, 2 Feb 1995 18:31:44 -0500 (EST)
Cc: bugtraq@fc.net
In-Reply-To: <199502021128.DAA16580@merde.dis.org> from "Pete Shipley" at Feb 2, 95 03:28:23 am
Back at the ranch, Pete Shipley scribed:
: >This is probably associated with the MAGIC PID SUBSYSTEM which has
: >been implemented on a number of popular UNIX's. Basically processes
: >that acquire a MAGIC PID have special powers and can do 'magical' things.
: >
: >If a hole is found in a program (such as /bin/login) which is executing
: >in a process with a MAGIC PID, it is said to have a 'magic hole'.
: >
: >LINUX is generally recognised as having the most complete MAGIC PID
: >implementation. The benefits of MAGIC PIDs was discussed widely on IRC's
: >#unix and #root about 12 months ago. For more info, I guess you could
: >try the usenet LINUX or security groups.
:
: gee like what magical things? please more detail..
From the file "MAGIC" in the top level of the Linux source tree:
"It is a *very* good idea to protect kernel data structures with magic
numbers. This allows you to check at run time whether (a) a structure
has been clobbered, or (b) you've passed the wrong structure to a
routine. This last is especially useful --- particularly when you are
passing pointers to structures via a void * pointer. The tty code,
for example, does this frequently to pass driver-specific and line
discipline-specific structures back and forth."
All the "magic number" is is an 'ID tag' that a module can test to assure
itself that it's private (or public) data structures haven't been overrun
by some other task.
Nice idea to help keep a kernel "sane" :-)
-Reto-
--
R A Lichtensteiger rali@hri.com
System Administrator Horizon Research Inc (617) 466-8304
Waltham MA 02154
http://www.hri.com/HRI/Pages/rali.html/
"The system has been practicing a noncomputational lifestyle ever
since the boot disk became I/O challenged."
