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* hard links create local DoS vulnerability and security problems
@ 2003-11-24 16:36 Jakob Lell
  2003-11-24 17:05 ` Måns Rullgård
                   ` (3 more replies)
  0 siblings, 4 replies; 38+ messages in thread
From: Jakob Lell @ 2003-11-24 16:36 UTC (permalink / raw)
  To: linux-kernel

Hello,
on Linux it is possible for any user to create a hard link to a file belonging 
to another user. This hard link continues to exist even if the original file 
is removed by the owner. However, as the link still belongs to the original 
owner, it is still counted to his quota. If a malicious user creates hard 
links for every temp file created by another user, this can make the victim 
run out of quota (or even fill up the hard disk). This makes a local DoS 
attack possible.

Furthermore, users can even create links to a setuid binary. If there is a 
security whole like a buffer overflow in any setuid binary, a cracker can 
create a hard link to this file in his home directory. This link still exists 
when the administrator has fixed the security whole by removing or replacing 
the insecure program. This makes it possible for a cracker to keep a security 
whole open until an exploit is available. It is even possible to create links 
to every setuid program on the system. This doesn't create new security 
wholes but makes it more likely that they are exploited.

To solve the problem, the kernel shouldn't allow users to create hard links to 
files belonging to someone else.

I could reproduce the problem on linux 2.2.19 and 2.4.21 (and found nothing 
about it in the changelogs to 2.4.23-rc3).

Regards
 Jakob


^ permalink raw reply	[flat|nested] 38+ messages in thread

end of thread, other threads:[~2003-11-25 16:23 UTC | newest]

Thread overview: 38+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2003-11-24 16:36 hard links create local DoS vulnerability and security problems Jakob Lell
2003-11-24 17:05 ` Måns Rullgård
2003-11-24 20:42   ` Mike Fedyk
2003-11-24 17:14 ` Richard B. Johnson
2003-11-24 17:35   ` Jamie Lokier
2003-11-24 18:57     ` aic7xxx loading oops in 2.6.0-test10 Alexander Nyberg
2003-11-24 20:03       ` Ken Witherow
     [not found]         ` <Pine.LNX.4.58.0311241524310.1245@morpheus>
2003-11-24 20:49           ` Ken Witherow
2003-11-24 23:42             ` Dick Streefland
2003-11-25  3:16     ` hard links create local DoS vulnerability and security problems Matthias Andree
2003-11-25 14:48     ` Jan Kara
2003-11-25 15:27       ` Jakob Lell
2003-11-24 17:37   ` Rudo Thomas
2003-11-24 18:10     ` Richard B. Johnson
2003-11-24 18:22       ` Valdis.Kletnieks
2003-11-24 22:17       ` [OT] " Rudo Thomas
2003-11-24 17:57   ` Jakob Lell
2003-11-24 18:08     ` splite
2003-11-24 18:13       ` Richard B. Johnson
2003-11-24 18:24         ` Jakob Lell
2003-11-24 23:57         ` bill davidsen
2003-11-24 18:18       ` Jakob Lell
2003-11-24 18:29         ` Valdis.Kletnieks
2003-11-24 19:25           ` hard links create local DoS vulnerability and security proble Mathieu Chouquet-Stringer
2003-11-24 20:00             ` Valdis.Kletnieks
2003-11-24 20:02               ` Mathieu Chouquet-Stringer
2003-11-24 20:22             ` H. Peter Anvin
2003-11-24 18:21     ` hard links create local DoS vulnerability and security problems Michael Buesch
2003-11-24 18:35       ` Jakob Lell
2003-11-24 18:53       ` Chris Wright
2003-11-25  0:04         ` bill davidsen
2003-11-25 13:54     ` Jesse Pollard
2003-11-24 23:50 ` bill davidsen
2003-11-25  0:22   ` Mike Fedyk
2003-11-25  0:35   ` Chris Wright
2003-11-25  8:15     ` Amon Ott
2003-11-25 16:11     ` Bill Davidsen
2003-11-25 11:26 ` Gianni Tedesco

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