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Re: MAGIC PIDs (was Re: magic??)Reto Lichtensteiger (ralihri.com)
Thu, 2 Feb 1995 18:31:44 -0500 (EST)
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- In reply to: Pete Shipley: "Re: MAGIC PIDs (was Re: magic??)"
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 ralihri.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."