Re: chmod from LSM

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mhalcrowat_private

On Wed, May 21, 2003 at 11:37:46AM -0700, Seth Arnold wrote:
> On Wed, May 21, 2003 at 10:36:36AM -0700, Michael Halcrow wrote:
> > Anyone have any good ways of chmod'ing a file from inside an LSM
> > module?  No hacks, please.  :-)
> 
> Take a look at sys_chmod() for some ideas how it should work. The kernel
> source most easily available to me appears to go through some hoops with
> struct iattr newattrs, performs the mode masking operations on the
> structure, then uses notify_change() to perform the modifications.
> (This is probably to assist tools such as the file access monitor, used
> in many explorer.exe-work-alikes.)
> 
> I hope this helps...

I've been trying to re-implement sys_chmod inside of my LSM, but I
keep getting errno=14 every time I use __user_walk to get the dentry
for my file.  This is the EFAULT error code, which indicates that one
of the arguments may be an invalid pointer.  I have checked my
pointers carefully, and they are valid.  I tried allocating the memory
those pointers point to via __get_free_page, but that did not help.
Is there some sort of dark magic that I have yet to become acquainted
with in order for this to work?

Mike

-- 
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Michael Halcrow                             | mhalcrowat_private 
Developer, IBM Linux Technology Center      |                      
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