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Re: Using VFS operations for a given node

On Jul 25, 2007, at 4:52 AM, Standard Azi wrote: 
As a general rule, if you think you want to initiate operations on
files, file attributes, pathnames etc. from the kernel you have made
a design error and need to stop and re-evaluate what you are doing.


That's usually true although I don't see any other method that is more
elegant - maybe you do, so let me explain what I'm trying to do :

===
- open() is hooked with Kauth

- if there is some special extended attribute set on the opening file,
handle some security issues before returning a file descriptor, else,
return the proper fd.
===

Do you see any other way to keep track of the files handled by the
security module? (please note that the extended attribute holds some
meaningful data for the kernel)


- open is trapped by a kauth module

- the kauth module send a message to a user space daemon that has registered with the kauth module earlier so that the module knows it's there and alive

- the user space daemon looks at the extended attribute information, and makes a decision

- if the user space daemon has to call any operations on the file that are trapped by the kauth module, then because it has registered with the module, it's operations are simply permitted, rather than recursively calling back out to user space

- the user space daemon igures out an answer

- the user spce daemon returns the answer to the kauth module

- the kauth module permits/denies the operation based on the answer it has received

Sure, now we can question about the purpose of the security module,
why it has to rely on userspace data, etc... but focusing on the
approach I've described, do you see any other solution to keep track
about which files to handle in a special manner?


See above.

In almost every case, what you are trying to do should be handled in
user space.

I'd say this is an exception.

I'd say it wasn't; most work, particularly work that could take a long time or block things long enough that they get a spinny beach ball/ wheel of fortune/pizza of death/whatever you like to call the cursor for an unresponsive application.

-- Terry
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References: 
 >Re: Using VFS operations for a given node (From: Michael Smith <email@hidden>)
 >Re: Using VFS operations for a given node (From: "Standard Azi" <email@hidden>)



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