Nethack setgid screwup
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Quoted 9 lines · Aaron Lehmann
----- Forwarded message from Alexander Viro <[email protected]> -----
Quoted 2 lines · Linus Torvalds
But I like Al's idea of mount binds even more, although it requires maybe a bit more administration.
OK, will do - will be fun to take a break from
drivers/*and devfs excrements I'm digging in...
Quoted 9 lines
BTW, here's a fresh demonstration (found half an hour ago) that capabilities do *not* permit more lax attitude when writing stuff with elevated priveleges:
*/usr/lib/games/nethack/recoveris run at the boot time (as root)
to recover crashed games.
* Debian nethack 3.4.0-3.1 has it installed root.games and it
is group-writable - cretinism in debian/rules, upstream is not guilty in that (BTW, so is/usr/lib/games/nethack/recover-helper).
* ergo, any exploitable hole in sgid-games binary (rogue, for
instance) is trivially elevated to root exploit.
mizar:[/tmp] dpkg -l nethack
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Installed/Config-files/Unpacked/Failed-config/Half-installed |/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad) ||/ Name Version Description +++-==============-==============-============================================ ii nethack 3.4.0-3.1 Overhead dungeon-crawler game (dummy package mizar:[/tmp] ls -l /usr/lib/games/nethack/recover* -rwxrwsr-x 1 root games 6088 2002-07-06 17:54 /usr/lib/games/nethack/recover -rwxrwxr-x 1 root root 283 2002-07-06 17:54 /usr/lib/games/nethack/recover-helper
mizar:[/tmp] grep recover /etc/init.d/nethack
# Nethack save-file recovery script for Debian
test -x /usr/lib/games/nethack/recover-helper || exit 0
# Refuse to recover root's nethack files.
echo "Ignoring root's Nethack unrecovered save file." # script running as the user which recovers everything su "$owner" -c /usr/lib/games/nethack/recover-helper
The script has worked this way since at least version 3.3.0-7, which is found in Debian 2.2 (potato). Is there some other situation you found where recover would be run as root, other than when explicitly started by root?
This is still a serious bug, of course, and allows gid games to be exploited to gain the privileges of a user with a recoverable saved game, but not root (at least not trivially).
Signature · 1 line
- mdz