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    SubjectRe: Anybody out there? (ETXTBSY)
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    In article <6s56qg$fo$1@palladium.transmeta.com>,
    torvalds@transmeta.com (Linus Torvalds) writes:
    > In article <19980827023536.C9225@dot.cygnus.com>,
    > Richard Henderson <rth@cygnus.com> wrote:
    >> On Wed, Aug 26, 1998 at 02:26:28PM -0500, pacman wrote:
    >>> Is nobody interested on getting ETXTBSY to work for shared libs? Come on,
    >>> take a break from the EFAULT wars and walk down the street to 26 Errno Lane
    >>> and tell me what you think.
    >>
    >> ETXTBSY is explicitly not set on shared libraries. If you turn
    >> it on, it is impossible to upgrade libc.so.

    > 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.

    > The reason MAP_EXECUTABLE isn't exported is programs like this:

    > fd = open("/var/spool/utmp");
    > mmap( ... fd ... MAP_EXECUTABLE ...);
    > sleep(forever); /* nobody is able to log in */

    > which used to actually happen.

    How about only allowing MAP_EXECUTABLE on files that have the x bit set?
    This would prevent this attack, and ETXTBSY could be properly implemented.

    Or do I miss something here?

    -Andi

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