Solving the process ID allocation problem [LWN.net]

Solving the process ID allocation problem

Posted Sep 25, 2002 13:51 UTC (Wed) by oneukum (subscriber, #3970)
In reply to: Solving the process ID allocation problem by cpeterso
Parent article: Solving the process ID allocation problem

The PID is an argument of some system calls. The kernel cannot for reasons of security,
accept a pointer into kernel memory which user spaces feeds it.
PIDs must be in some kind of table, so that they can be verfied.

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Solving the process ID allocation problem

Posted Sep 29, 2002 17:40 UTC (Sun) by GreyWizard (subscriber, #1026) [Link]

The kernel cannot for reasons of security, accept a pointer into kernel memory which user spaces feeds it.

Well, sure. But that's not what was suggested. Just because a valid process identifier is identical to the memory address of a process struct doesn't mean the kernel can't look it up values passed in from user space in a hash table before acting on them. The code that creates processes would cast the pointer and the rest of the system would remain unchanged.

(I agree this makes a PID hard to type, especially on 64 bit systems, but things like job control and terminal cut-and-paste mitigate this somewhat.)