Bugtraq mailing list archives

Re: FreeBSD-specific denial of service

From: bfischer () TECHFAK UNI-BIELEFELD DE (Bjoern Fischer)
Date: Fri, 24 Sep 1999 10:06:44 +0200


On Tue, Sep 21, 1999 at 03:50:58PM -0400, Charles M. Hannum wrote:

Here's an interesting denial-of-service attack against FreeBSD >=3.0
systems.  It abuses a flaw in the `new' FreeBSD vfs_cache.c; it has no
way to purge entries unless the `vnode' (e.g. the file) they point to
is removed from memory -- which generally doesn't happen unless a
certain magic number of `vnodes' is in use, and never happens when the
`vnode' (i.e. file) is open.  Thus it's possible to chew up an
arbitrary amount of wired kernel memory relatively simply.


This has been addressed and was fixed in src/sys/kern/vfs_cache.c
revision 1.38.2.3 before releasing the latest stable FreeBSD-3.3:

A tunable sysctl knob `vfs.cache.maxaliases' which defaults to 4
limits the number of cache aliases to a vnode.

  Björn Fischer

-- 
(sig_t*)NULL

<!-- attachment="bin0a27613" -->
<HR>
<UL>
<LI>application/pgp-signature attachment: stored
</UL>

Current thread:

Re: fixing all buffer overflows --- random magin numbers nm (Sep 12)
- Re: fixing all buffer overflows --- random magin numbers Crispin Cowan (Sep 13)
  - Re: fixing all buffer overflows --- random magin numbers Oliver Xymoron (Sep 17)
    - Exploit for proftpd 1.2.0pre6 Tymm Twillman (Sep 20)
    - Re: fixing all buffer overflows --- random magin numbers Crispin Cowan (Sep 20)
    - BP9909-00: cfingerd local buffer overflow Przemyslaw Frasunek (Sep 21)
    - Windows IP source routing attack Dug Song (Sep 21)
    - FreeBSD-specific denial of service Charles M. Hannum (Sep 21)
    - Re: FreeBSD-specific denial of service Alan Cox (Sep 22)
    - Re: FreeBSD-specific denial of service Bjoern Fischer (Sep 24)