[Full-disclosure] Possible security issue with FreeBSD 5.4 jailing and BPF

[Simon L. Nielsen]

On 2005.07.11 23:54:15 +0200, ronvdaal wrote:

> While playing around with FreeBSD 5.4 and jailing I discovered that it was
> possible to put an ethernet interface into promiscious mode from within the
> jailed environment, allowing a packetsniffer to gather data not meant for
> the jailed box. This also affects FreeBSD 5.3 (tested) but not FreeBSD 4.x
> This can be reproduced on boxes where BPF support is enabled in the kernel
> and a BPF device is available in the jail (badly configured devfs/no rules)
[...]
> Usage of devfs rulesets is highly recommended as stated in the manpages.
> Though a misconfiguration at this point would expose a big security issue.
> The question is: should bpfopen() in bpf.c check for a jailed proc or not?

This is not really a security bug since, as stated in the jail(8)
manual, you should use devfs rulesets if you are using jails as a
security measure.  Exposing a complete /dev file-system inside a jail
is a bad idea security wise, not just with regards to BPF.

-- 
Simon L. Nielsen
FreeBSD Security Team
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