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rm.racecondition

rm.racecondition
Posted May 17, 2000
Authored by Morten Welinder

If root ever does "rm -rf /tmp/foo" for a directory structure not completely owned by root, a local user can delete all files that root can.

tags | exploit, local, root
SHA-256 | 3ba1f58d2454e57c2aabb1552bf4229866c003b9fde29b9e8099400b1fef591c

rm.racecondition

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Synopsis:

If root ever does "rm -rf /tmp/foo" for a directory structure
not completely owned by root, a local user can delete all files
that root can.

Such deletions are common for (a) /tmp cleanup and (b) before
creating a specific directory in /tmp/.


Details:

"rm -r" implementations (Solaris 7, Gnu 4.0 checked) walk the
directories, lstats files, and chdirs into directories (and
recurs). Oh, and deletes stuff, of course.

It is possible to replace a directory by a symlink, say "/",
and have rm cheerfully follow it.

The race window is small -- it will take thousands upon thousands
of tries. Moreover, since the racing involves rmdir -- which
typically is not very fast -- you'll need patience and "nice"
and any other help you can get.


Solutions:

Maybe stat "." after chdir to verify that we ended up the
expected place?


Also affected:

chmod, chown, chgrp. (Probably; this is guesswork.)
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