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Cook: seccomp filter now in UbuntuCook: seccomp filter now in UbuntuPosted Mar 26, 2012 23:51 UTC (Mon) by slashdot (guest, #22014)In reply to: Cook: seccomp filter now in Ubuntu by luto Parent article: Cook: seccomp filter now in Ubuntu
Isn't removing the seccomp filter on setuid execution a better solution than requiring nnp?
Of course, applications could elect to use nnp anyway, but why force it?
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Cook: seccomp filter now in Ubuntu Posted Mar 26, 2012 23:56 UTC (Mon) by luto (subscriber, #39314) [Link]
Because then a task could break out of seccomp mode 2 by running a setuid program. That would IMO rather defeat the purpose.
I suspect that the average system has any number of setuid binaries installed that allow you to run arbitrary code as yourself, since that wouldn't normally be considered a security problem. As a trivial example:
$ sudo -u luto -s
does not prompt for a password.
Cook: seccomp filter now in Ubuntu Posted Mar 27, 2012 0:14 UTC (Tue) by slashdot (guest, #22014) [Link]
Well, one could indeed use nnp to avoid that, or conversely they could prepare a chroot or FS namespace with no or select setuid programs.
But maybe it's good to require it, to prevent people accidentally introducing security holes because they don't know they either need to use nnp, restrict execve or use a filesystem namespace.
Cook: seccomp filter now in Ubuntu Posted Mar 27, 2012 0:18 UTC (Tue) by luto (subscriber, #39314) [Link]
Unprivileged users can't chroot (yet [1]) or use FS namespaces. And correctly detecting when execve(2) will run a setuid program is probably impossible except in very limited circumstances.
[1] https://git.kernel.org/?p=linux/kernel/git/luto/linux.git;... [but I doubt that patch will be accepted in its current form]
Cook: seccomp filter now in Ubuntu Posted Mar 27, 2012 0:33 UTC (Tue) by slashdot (guest, #22014) [Link]
Unprivileged users have to use nnp anyway.
Privileged users, in theory, could instead want to setup a FS namespace with some setuid programs of their choice.
However, this is probably useless in practice, so indeed it may be better to avoid the risk of an accidental security hole and force nnp on.
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