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Re: Kernel authorization (Kauth) from user space



On 10/11/07, Jernej Azarija <email@hidden> wrote:

>
>  > 1) The recommended way from the technical documentation is to read/write
> in
>  >kernel, but all the mailing lists discussions say to do it in user space.
>  In userspace? It depends on what you need to accomplish.

I need to read and/or write from/to files in both fileop scope and
vnode scope listeners.

>
>  > 2) Assuming that I send the path from kernel to the user space daemon
>  >(returned by vn_getpath from the vnode parameter) , I have the following
>  >issues:
>
>  Actually, one of the kauth hook function arguments is the relevant path
> name  -
>  you just have to cast it to (char *).
>
>
>  >        - for files with paths longer than MATXPAHTLEN (1024) , which can
> be
>  >created with Finder:
>  >                - vn_getpath returns error 28 (KERN_INVALID_POLICY)
>  >                - the callback for OPEN/CLOSE actions is called with empty
>  >path (arg1) or it's not called at all
>
>  Use the supplied path as said. You'll only have to play about transfering
> the path to userspace.

In the vnode listener you have no path. Please read all the message.

>
>  > 4) Another possible solution seems  to be using VNOP_READ/VNOP_WRITE in
>  >kernel space and transfer data to daemon
>
>  If you only need to hook open/close, use KAUTH_SCOPE_FILEOP. It's not
> reasonable to hook VNODE operations - at last from the performance view.

I don't want to hook the operations, I want to use them for read or
write from/to files.
Opening a path in user mode is ok if the paths can be always retrieved
(vn_getpath or listener argument), are limited and the userland's open
doesn't have problems with exclusive accesses.
If not then a different approach is needed, the points 3) and 4) from
the initial post are possible solutions. Or maybe there's another one
!?

Thanks,

 Liviu
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References: 
 >Kernel authorization (Kauth) from user space (From: "Liviu Andron" <email@hidden>)
 >RE: Kernel authorization (Kauth) from user space (From: "Jernej Azarija" <email@hidden>)



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