Re: Anybody out there? (ETXTBSY)

pacman (pacman-kernel@cqc.com)
Fri, 28 Aug 1998 14:18:52 -0500 (EST)

Linus Torvalds writes the following:
>
>No, the reason ETXTBSY is dangerous is mainly because it's a great
>denial-of-service thing. As such, the MAP_EXECUTABLE thing that Linux
>uses internally is not exported to user level, and as such the loader
>can't use it even if it wished.

s/MAP_EXECUTABLE/MAP_DENYWRITE/

My patch (http://www.linuxhq.com/lnxlists/linux-kernel/lk_9808_04/msg00086.html)
gets around that problem by making ETXTBSY a side effect of mmap(PROT_EXEC),
and by checking PROT_EXEC against the x permission bit. This eliminates the
security problem, and also pretty much eliminates the need for MAP_DENYWRITE
as a separate flag, but I didn't go so far as to remove it.

In case you missed it, my original post
(http://www.linuxhq.com/lnxlists/linux-kernel/lk_9808_03/msg01132.html)
brought up some other questions you might want to consider, but it also
contains a bad version of the patch, so don't use that one

-- 
Alan Curry


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