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Re: Userland filesystems and LD_PRELOAD


Jani,
There was discussion of this issue a couple of months
back. The issue was well covered at the time. 

The archives are probably the best place to look.

http://www.ecn.wfu.edu/glibc-linux-archive


Troy


> 
> 
> I am interested in userland filesystems using system call hooking and
> no kernel support (not even Coda or NFS). However in the documentation of
> one such filesystem, avfs (http://www.inf.bme.hu/~mszeredi/avfs/) there
> reads:
> 
> <CLIP>
> The 'preload' method works by "overriding" the system calls in the
> libc library, and replacing them with versions that can emulate
> virtual files.
> 
> Since GLIBC 6.1 this "overriding" is made impossible for many
> systemcalls, and so this method cannot be used anymore. This change
> and its effects have been discussed with the GLIBC developers, and the
> result has been that it will remain so in the future.
> </CLIP>
> 
> So how and why is this overriding made impossible?
> 
> I think there would be software who could use this method, if hooking
> filesystem calls (just like hooking malloc, DNS and user database) would
> be possible. And not all users have root access (so they cannot use
> kernel tricks).
> 
> - Jani
> 
> 


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